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Genetic improvement of grain crops: yield potential
... Similar increases were reported by FAO (2017) and , exploring a wider spread in time (90+ years). Yield improvement over time has been mainly explained as a result of greater plant biomass and increases in harvest index (Sinclair, 1998;Koester et al., 2014;Gaspar et al., 2017; via plant physiological changes such as longer growth in reproductive period (Gay et al., 1980;Kumudini et al., 2001;Egli and Cornelius, 2009;Rowntree et al., 2014;, implementation of better management practices (Luedders, 1977;Frederick et al., 1991;Heatherly and Elmore, 2004;Conley and Santini, 2007;, and genetic advancements Wilcox et al., 1979;Specht and Williams, 1984;Voldeng et al., 1997;Foulkes et al., 2009;Rincker et al., 2014;Wilson et al., 2014;de Felipe et al., 2016). Nonetheless, global annual rate for soybean yield increase reported in the last decades (~1.3%) represents only about half of the ~2.4% projected estimations to ensure enough production by 2050(Ray et al., 2013. ...
... Rowntree et al. (2013) documented a negative effect on seed protein concentration as yield increased, with a 0.19 g kg -1 decrease per year for maturity group (MG) II and 0.24 g kg -1 decrease for MG III, all relative to the 1920s and 2000s period. Changes in seed yield and seed protein concentration were a consequence of both genetic Specht and Williams, 1984;Voldeng et al., 1997;Foulkes et al., 2009;Wilson et al., 2014;de Felipe et al., 2016) and management practices (Frederick et al., 1991;Heatherly and Elmore, 2004;Conley and Santini, 2007;. ...
... Among relevant management practices were: earlier planting dates (Conley and Santini, 2007;, use of conservation tillage, narrow row spacing, reduction of harvest losses (Heatherly and Elmore, 2004), and improvements in weed management . On the other hand, reported genetic improvements in plant traits were disease resistance (Foulkes et al., 2009), elongation (time) of the reproductive stages and, consequently, longer seed filling (Gay et al., 1980), shorter vegetative period favoring longer reproductive periods , and a reduction in lodging (Specht and Williams, 1984). , summarized yield improvements (from 1922 to 2015) primarily impacting biomass production, resulted from both management practices and genetic improvements. ...
Soybean [Glycine max (L.) Merr.] yields have continuously increased over time. Seed yields are determined by the genotype, environment, and management practices (G × E × M) interaction. Closing yield gaps require a continuous improvement in the use of the available resources, which must be attained via implementation of better management decisions. Linear relationships between seed yield and nitrogen (N) demand are reported in the scientific literature. Main sources of N to the plant are the biological N fixation (BNF) and the soil mineralization processes. On overall, only 50-60% of soybean N demand is met by the BNF process. An unanswered scientific knowledge is still related to the ability of the BNF to satisfy soybean N demand at varying yield levels. Seed N demand not met by N fixation plus soil mineral N, is then fulfilled by the remobilization of N from vegetative organs during the seed filling period. An early remobilization process reduces the photosynthetic activity (leaves) and can limit seed yield. The objectives of this project were to: i) study yield improvements and contribution of N via utilization of contrasting N conditions under historical and modern soybean genotypes, and ii) quantify main seed N sources during the seed filling period. For objective one, four field experiments were conducted during the 2016 and 2017 growing seasons in Kansas, United States (US) and Santa Fe Province, Argentina (ARG). Those experiments investigated twenty-one historical and modern soybean genotypes with release decades from 1980s to 2010s. As for objective two, three field experiments were conducted during the 2015 and 2016 growing seasons in Kansas, US, studying three soybean genotypes: non-roundup ready (RR), released in 1997; RR-1, released in 2009; and RR-2, released in 2014. Across all studies, seeds were inoculated and tested under three N management strategies: i) control without N application (Zero-N); ii) 56 kg N ha⁻¹ applied at reproductive growth stages (Late-N); and iii) 670 kg ha⁻¹ equally split at three timings (Full-N). As for yield improvements and N limitation, soybean yield improvements from the 1980s to 2010s were documented, representing 29% increases in the US and 21% in ARG. Regarding N management, the Full-N fertilization produced a 12% increase in seed yields in the US and 4% in ARG. As for main seed N sources in objective two, remobilization accounted for 59% of seed N demand, and was negatively related to new N uptake occurring during the seed filling period. Seed N demand for greater yields was dependent on both, N remobilization and new N uptake, while for lower yields, seed N demand was mainly supported by the N remobilization process. These results suggest that: a) high seed yields are somehow limited by the availability of N to express their potential, although the question about N application still remains to be fully investigated, as related to the timing and the environment by plant interactions that could promote a N limitation in soybeans; b) remobilization accounts for majority (59%) of N sourced to the seed, and c) high yielding soybean (modern genotypes) rely on diverse N sources: the N remobilization process plus new uptake of N.
... With the increasing world population, which is estimated to reach 9.4 billion by 2050(Foulkes et al., 2009, global agriculture in the 21st century is facing a significant increase in crop production. Wheat is one of the most important major food sources providing more than 20% of human calorie consumption (Merchukovnat et al., 2016). ...
... Since the 1960s, it has been suggested that increases in the harvest index (HI; the proportion of total dry matter (DM) allocated to harvested grains) result in an increase in grain yield (Nass, 1980;Slafer et al., 1994;Qin et al., 2013). Thus, with the development of wheat breeding, the mean HI of wheat has experienced an increase from 0.35 in 1951-1955to 0.5 in 1995(Evans and Fischer, 1999Foulkes et al., 2009;Wiesmeier et al., 2014), while Austin (1980) predicted that the HI of modern winter wheat could reach a maximum of 0.62. Therefore, since the HI of modern cultivars is already high, it has been suggested that further improvements in yield will rely more on increases in total DM ( Aranjuelo et al., 2013;Parry and Hawkesford, 2010;. ...
... Recently, increases in wheat yield have been attributed to increases in HI ( Foulkes et al., 2009;Aranjuelo et al., 2013). Moreover, since the green revolution and genetic improvements in breeding, HI values have continued to reach high levels ( Wiesmeier et al., 2014;Fan et al., 2017). ...
Both increased harvest index (HI) and increased dry matter (DM) are beneficial to yield; however, little is known about the priority of each under different yield levels. This paper aims to determine whether HI or DM is more important and identify the physiological attributes that act as indicators of increased yield. Two field experiments involving different cultivation patterns and water-nitrogen modes, respectively, were carried out from 2013 to 2016 in Huang-Huai Plain, China. Plant DM, leaf area index (LAI), and radiation interception (RI) were measured. Increased yield under low yield levels <7500 kg ha⁻¹ was attributed to an increase in both total DM and HI, while increases under higher yield levels >7500 kg ha⁻¹ were largely dependent on an increase in HI. Under high yield levels, HI showed a significant negative correlation with total DM and a parabolic relationship with net accumulation of DM during filling. Higher net accumulation of DM during filling helped slow down the decrease in HI, thereby maintaining a high value. Moreover, net DM accumulation during filling was positively correlated with yield, while post-anthesis accumulation showed a significant linear relationship with leaf area potential (LAP, R² = 0.404–0.526) and radiation interception potential (RIP, R² = 0.452–0.576) during grain filling. These findings suggest that the increase in LAP and RIP caused an increase in net DM accumulation after anthesis. Under DM levels >13,000 kg ha⁻¹ at anthesis, maintaining higher LAI and RI in lower layers during grain formation contributed to higher yield. Furthermore, the ratio of upper- to lower-layer RI showed a second-order curve with yield during filling, with an increase in the optimal range with grain development. Pre-anthesis translocation amount, translocation ratios and contribution ratios also showed second-order curves under high yield levels, with optimal values of 3000–4500 kg ha⁻¹, 25–35, and 30–50%, respectively. These results confirm the importance of HI in improving the yield, thereby providing a theoretical basis for wheat production in the Huang-Huai Plain.
... RUE is largely determined in cereal crops by the interception of light necessary for photosynthesis (especially after canopy closure) and the phenological stage. Thus, the angle adjustment of the leaf and canopy architecture has an important role in the photosynthesis and productivity of these crops [118,123,124]. Modern varieties of cereal crops (e.g., wheat, rice) have more erect leaves [124,125], facilitating the penetration of light into the lower layers of the canopy. ...
... Thus, the angle adjustment of the leaf and canopy architecture has an important role in the photosynthesis and productivity of these crops [118,123,124]. Modern varieties of cereal crops (e.g., wheat, rice) have more erect leaves [124,125], facilitating the penetration of light into the lower layers of the canopy. It has been suggested that an ideal plant ideotype in cereals is one that has an increased leaf angle from the top to the basal layers of the canopy [126][127][128]. ...
Increased periods of water shortage and higher temperatures, together with a reduction in nutrient availability, have been proposed as major factors that negatively impact plant development. Photosynthetic CO2 assimilation is the basis of crop production for animal and human food, and for this reason, it has been selected as a primary target for crop phenotyping/breeding studies. Within this context, knowledge of the mechanisms involved in the response and acclimation of photosynthetic CO2 assimilation to multiple changing environmental conditions (including nutrients, water availability, and rising temperature) is a matter of great concern for the understanding of plant behavior under stress conditions, and for the development of new strategies and tools for enhancing plant growth in the future. The current review aims to analyze, from a multi-perspective approach (ranging across breeding, gas exchange, genomics, etc.) the impact of changing environmental conditions on the performance of the photosynthetic apparatus and, consequently, plant growth.
... To avoid the rapid leaching of nitrate from the soil, the primary root traits including rooting depth and rooting density are important to improve N capture, particularly N uptake during grain filling stage (Foulkes, Reynolds, and Sylvester-Bradley 2009). Rooting length and root biomass accumulation follow a pattern, with the rapid increase during early stage of plant life cycle Figure 3. Diagrammatic representation of core enzymes that take parts in N uptake from soil, how it's assimilate and remobilize from roots to leaves (during vegetative) and leaves to developing seeds (at senescence).; ...
... Despite strong environmental influence (nutrient availability, soil characteristics, and mechanical impedance) on root distribution, genotypic variation for root architect (Ford et al. 2006) is reported in wheat. Rooting depth goes up to 200 and 120 cm cm in winter and spring wheat, respectively (Foulkes, Reynolds, and Sylvester-Bradley 2009). As crop with longer duration has deeper roots (Barraclough, Weir, and Kuhlmann 1991), the larger rooting depth in winter wheat may also probably be due to longer vegetative phase. ...
Increased application of inorganic nitrogen has been the key component responsible for growth in cereal production. Due to continuously increasing application of Nitrogen (N) and its lower use efficiency along with environmental and health implications of leftover N, improving nitrogen use efficiency (NUE) through management and genetic manipulation require immediate attention. The way N is uptaken through better root architecture and improved transporters and assimilated and remobilized into storage organ influences NUE. Partitioning of N between leaves and stems, photosynthetic efficiency, rubisco activity and senescence of leaf decide N utilization efficiency. Genetic manipulation to improve NUE requires information on the extent of exploitable genetic variability and their genetic control, however, limited information about these traits limits development of efficient genotypes. MAS for QTLs associated with key enzymes involved in N uptake and utilization or transgenic by overexpress-ing the enzymatic gene shows great promise in the future. Furthermore, the interaction of NUE and other plant traits should be evaluated.
... Shortening the period between appearance of two successive leaves and increase of FLN (Valle and Calderini 2010) hastens canopy closure and improves leaf area index and the radiation in- terception during early vegetative development ( Foulkes et al. 2009). Further, by simultaneously shortening PHY and increasing FLN, a cultivar may have higher leaf area development without modification of AD. ...
... Assimilates stored in vegetative parts during the period to AD are im- portant for maintenance of YIL when the process of photosynthesis is reduced by different abiotic factors (Dordas 2012). Furthermore, as the result of breeding progress, modern wheat and barley cultivars reached already high values of harvest index and genetic improvement cannot be a result of further increase of the harvest index ( Foulkes et al. 2009). Therefore, increasing biomass with maintaining or even improving the harvest index is one of the potential goals in cereal breeding. ...
The aim of this study was to improve understanding of (1) the effect of genotypic and environmental factors on pre-anthesis development and leaf appearance traits of barley and wheat; (2) the relationship of these factors with grain yield, and (3) the differences between these two crops across different environments/sowing dates. Therefore, trials with six two-row winter barley and six winter wheat cultivars were carried out in two successive growing seasons on four sowing dates. Our study showed that the observed traits varied between species, cultivars and sowing dates. In both growing seasons, biomass at anthesis and grain yield declined almost linearly by delaying the sowing date. There was no clear advantage in grain yield of wheat over barley under conditions of later sowing dates. Generally, barley produced more leaf and had shorter phyllochron than wheat. Both wheat and barley showed a similar relationship between grain yield and different pre-anthesis traits.
... India is the second largest consumer of nitrogen fertilizers in the world after China [1]. Therefore, developing new cultivars that uptake and utilize N more efficiently to produce grain yield will be of economic benefit to farmers in India and will help to reduce environmental contamination associated with inputs of N fertilizers [2,3]. N-use efficiency (NUE) can be defined as the grain dry matter (DM) yield (kg DM ha −1 ) divided by the supply of available N from the soil and fertilizer (kg N ha −1 ; [4]) and can be divided into two components: (i) N-uptake efficiency (NUpE; above-ground N uptake per unit N available) and (ii) Nutilization efficiency (NUtE; grain dry matter yield per unit above-ground N uptake). ...
... For example, GW-322 is a cultivar from the Gujrat breeding zone which is traditionally a breeding zone for drought tolerance and this cultivar may have selected for better rooting traits resulting in high NUpE.NUtE showed a positive correlation with NUE and grain yield under HN conditions. If NHI (grain N / AGN H ) remains unchanged, then increasing NUtE will result increased grain N%[2]. The two highest yielding cultivars under HN (PDW-314, GW-322) also maintained GY better than other genotypes ...
Nitrogen (N) fertilizer represents a significant cost for the grower and may also have environmental impacts through nitrate leaching and N 2 O (a greenhouse gas) emissions associated with denitrification. The objectives of this study were to analyse the genetic variability in N-Use efficiency (grain dry matter (DM) yield per unit N available from soil and fertilizer; NUE) in Indian spring wheat cultivars and amphidiploid lines and identify traits for improved NUE for application in breeding. Thirty Indian elite cultivars and twenty amphidiploid lines along with five bread wheat parents were tested under two levels of N in a field experiment at Agharkar Research Institute, Pune, India and a glasshouse experiment at Nottingham University, UK, respectively. Detailed growth analysis was conducted including DM and N partitioning at anthesis and at harvest in the field experiment and at harvest in the glasshouse experiment. In the field experiment under low N grain yield was reduced on average by 1.45 t ha −1 (29%). Crop above-ground N uptake at harvest on average was reduced from 14.5 kg N ha −1 under high N (HN) to 8.0 kg N ha −1 under LN conditions while N-utilization efficiency (grain DM yield per unit above-ground N uptake at harvest; NUtE) increased from 34.2 to 44.2 g DM g −1 N. Significant N × genotype level interaction was observed for NUtE. Overall genetic variability in NUE was in the range 11.8-23.4 g DM g-1 N under LN (P<0.001) related mainly to differences in N-Uptake Efficiency (above-ground N uptake at harvest per unit N available from soil and fertilizer; NUpE) rather than N-utilisation efficiency (NUtE). In a glasshouse experiment, out of twenty amphidiploid lines, four lines under HN conditions and four lines under LN conditions showed significantly higher leaf photosynthesis rate than their parental bread wheat. In addition, higher expression than the bread wheat parent was observed for Thinopyrum. turcicum P208/201 x Chinese Spring Eup 94, Secale anatolicum P208/142 x Highbury and Secale anatolicum P208/141 x Chinese Spring Eup 94 for grain yield, above-ground dry matter and above-ground N showing potential to exploit these genotypes for wide crossing for NUE breeding.
... Over a century, selection for yield has delivered a linear increase in yield per unit water use of Australia's wheats, highlighting the effectiveness of this direct approach (Sadras and Lawson, 2013). Breeding, physiological and genetic perspectives converge to recognise the fundamental link between yield potential and stress adaptation (Thomson and Lee, 1980;Richards, 1995;Foulkes et al., 2009;Fleury et al., 2010;Sadras and Lawson, 2013). Consistent with this notion, pea accessions with greater capacity to capture the benefits of good environments also performed better where heat and water stress are prevalent. ...
... Consistently, in this study yield correlated with seed number and was statistically unrelated with seed size. Seed number is defined in a species-dependent developmental window (Fischer, 1985;Guilioni et al., 2003;Foulkes et al., 2009;Sandaña and Calderini, 2012). Environmental and genotypic sources of variation that affect crop growth rate during this stage have direct consequences for seed set and algorithms relating growth rate and seed number are commonly used in crop simulation models (Charles-Edwards, 1984;Gerik et al., 2004;Andrade et al., 2005;Hammer et al., 2010). ...
We compared 29 pea (Pisum sativum L.) accessions including advanced breeding lines and commercial varieties in environments spanning a 3-fold range in yield. Environmental variation in yield was primarily accounted for by modelled water availability and maximum temperature in a window from 400 °Cd before to 200 °Cd after flowering. Our aims were to investigate (i) the trade-off between yield under stress and yield under favourable conditions, and (ii) the associations between yield and two traits: growth rate in a critical developmental window, and pod wall ratio (pod wall weight/whole pod weight).
... The number and size of developing grains on the wheat spike can affect the overall sink strength, and wheat genotypes with a greater number of grains or larger grains generally have a higher sink strength, allowing them to attract and utilize more assimilates [14,15]. Therefore, studying yield components related to grain number and size could help to better understand the genetic basis for increasing wheat production [4,8,13,[16][17][18][19]. ...
Creating wheat genotypes characterized by high grain yield, high protein content, and favorable amino acid composition is the main goal of breeders, especially in developing countries where wheat is a staple food. An experiment with 20 wheat genotypes, released through breeding activities in the Serbian region at different periods and adapted to its pedoclimatic conditions, was conducted with the aim of determining the genetic potential of the analyzed genotypes for grain yield and quality. Due to the divergence of the examined wheat germplasm, the factor of genotype had the largest share in the variation of all yield parameters (>66%). The genotypes Zadruga and Agrounija exhibited superior abilities for overall grain yield. Also, genotype Zadruga stood out in a distinct cluster group due to high values of both thousand grain weight and grain yield per plant. A continuous improvement in protein content was found, with newer genotypes having 17.13% higher protein content compared with older genotypes. Genotype Sloga stood out with the highest protein content (13.93%). On the other hand, the old genotype Balkan was distinguished by the highest content of nonessential amino acids (61.5 g 100 g−1 protein), which makes it a good genetic resource. Genotypes Agrounija (32.62 g 100 g−1 protein) and Tanjugovka (32.47 g 100 g−1 protein) had the highest content of essential amino acids. The highest AAS value was established for tryptophan (1.81) and the lowest for lysine (0.61). Genotypes Tanjugovka and Zadruga had the highest AAS, i.e., protein completeness. The genotypes Zadruga, Tanjugovka, Agrounija, and Sloga have demonstrated high-yield capacity and possess a favorable amino acid profile, making them promising candidates for enhancing the nutritional quality of wheat and potentially benefiting human health.
... HI has shown a positive correlation with YD as previously documented in different studies (Yang and Zhang 2010;Duan et al. 2018;Porker et al. 2020). The positive association between yield and HI could be of major significance in encouraging breeders in their exploration for increased yield in wheat varieties (Foulkes et al. 2009;Aranjuelo et al. 2013;Duan et al. 2018). ...
The wheat–rye 1RS.1BL translocation has been extensively utilized in wheat breeding programs across the world for multiple disease resistances, abiotic stress tolerance and higher grain yield. The Sec-1 locus present on the 1RS and codes for rye storage protein secalin which causes stickiness in the dough leading to poor bread quality. In addition to this, the absence of Glu-B3/Gli-B1 on 1BS in this translocation further deteriorates the bread-making quality of wheat. In the present study, Pavon MA1 was used as the donor parent, and two elite wheat cultivars HS240 and UP2338, having 1RS.1BL translocation, were used as the recipient parents. Pavon MA1 has 1RSWW.1BL translocation in which the Sec-1 locus is absent whereas Glu-B3/Gli-B1 is present. This 1RSWW.1BL translocation was introgressed in the two wheat cultivars using marker-assisted backcross breeding, and BC2F5 derivatives were developed for both the cultivars. The dough quality of these derivatives was analyzed through the micro-SDS-sedimentation test (MST), high-molecular-weight glutenin subunits (HMWGS), loaf volume and micro-dough laboratory test. The dough analysis showed that the elimination of secalin in the derivatives led to the higher loaf volume, dough development time, dough stability and water absorption thus improving its bread-making quality.
... In Italy, De Vita et al. [10] and Pecetti and Annicchiarico [11] reported similar yield increases during the 20th century, with values of 19.9 and 17 kg ha −1 year −1 , respectively. In Spain, Chairi et al. [12] reported yield gains in durum wheat of 24 Focusing study on yield-related traits could help to better understand the genetic basis involved in wheat yield improvement [13]. Grain yield improvements in bread and durum wheat, including pre and post Green Revolution cultivars, have been mainly associated with increases in the harvest index and decreases in plant height due to the greater partition of assimilates to the reproductive organs [14][15][16]. ...
Understanding the basis of genetic gains in grain yield and yield-related traits is essential for designing future breeding strategies that lead to the development of higher-yielding wheat cultivars. The objectives of this study were to assess the changes in grain yield achieved by durum wheat breeding in Argentina and to identify the agronomic traits associated with these changes. To this end, a wide set of Argentinian cultivars was analyzed in three field trials. A significant linear trend (R2 = 0.55) was observed between the grain yield and the cultivar’s release year, with an increase of 26.94 kg ha−1 yr−1 from 1934 to 2015. The harvest index and grain number were key traits that explained the increases in grain yield. The number of grains per plant increased with the cultivar’s release year, while the thousand kernel weight remained unchanged. The grain yield showed an increase of 51% when comparing old cultivars (<1980) with intermediate ones (1980–1999), whereas the increase between intermediate and modern cultivars (2000+) was only 16%. Thus, the genetic gains were mostly associated with the incorporation of semi-dwarfism into the germplasm in the 1980s, with low genetic gains after that.
... HI has shown a positive correlation with YD as previously documented in different studies (Yang and Zhang 2010;Duan et al. 2018;Porker et al. 2020). The positive association between yield and HI could be of major significance in encouraging breeders in their exploration for increased yield in wheat varieties (Foulkes et al. 2009;Aranjuelo et al. 2013;Duan et al. 2018). ...
Introgression of genes from related species can be a powerful way to genetically improve crop yields, but selection for one trait can come at the cost to others. Wheat varieties with translocation of the short arm of chromosome 1 from the B genome of wheat (1BS) with the short arm of chromosome 1 from rye (1RS) are popular globally for their positive effect on yield and stress resistance. Unfortunately, this translocation (1BL.1RS) is also associated with poor bread making quality, mainly due to the presence of Sec-1 on its proximal end, encoding secalin proteins, and the absence of Glu-B3/Gli-B1-linked loci on its distal end, encoding low molecular weight glutenin subunits (LMW-GS). The present study aims to replace these two important loci on the 1RS arm with the wheat 1BS loci, in two popular Indian wheat varieties, PBW550 and DBW17, to improve their bread-making quality. Two donor lines in the cultivar Pavon background with absence of the Sec-1 locus and presence of the Glu-B3/Gli-B1 locus, respectively, were crossed and backcrossed with these two selected wheat varieties. In the advancing generations, marker assisted foreground selection was done for Sec-1− and Glu-B3/Gli-B1+ loci while recurrent parent recovery was done with the help of SSR markers. BC2F5 and BC2F6 near isosgenic lines (NILs) with absence of Sec-1 and presence of Glu-B3/Gli-B1 loci were evaluated for two years in replicated yield trials. As a result of this selection, thirty promising lines were generated that demonstrated improved bread making quality but also balanced with improved yield-related traits compared to the parental strains. The study demonstrates the benefits of using marker-assisted selection to replace a few loci with negative effects within larger alien translocations for crop improvement.
... Unfortunately, the HI of rapeseed remains much lower than that of other major crops, such as rice, wheat, maize (Zea mays), and soybean (Glycine max) (Hay, 1995;Unkovich et al., 2010). The HI for rapeseed ranges from 0.05 to 0.42 , which is far below the theoretical biological limit for HI of ∼0.60 in grain crops (Foulkes et al., 2009), indicating the potential to further increase HI. Therefore, improving HI in rapeseed varieties is a major objective for breeders. ...
Harvest index (HI), the ratio of harvested seed weight to total aboveground biomass weight, is an economically critical value reflecting the convergence of complex agronomic traits. HI values in rapeseed (Brassica napus) remain much lower than in other major crops, and the underlying regulatory network is largely unknown. In this study, we performed mRNA and small RNA sequencing to reveal the mechanisms shaping HI in B. napus during the seed-filling stage. A total of 8,410 differentially expressed genes (DEGs) between high-HI and low-HI accessions in four tissues (silique pericarp, seed, leaves, and stem) were identified. Combining with co-expression network, 72 gene modules were identified, and a key gene BnaSTY46 was found to participate in retarded establishment of photosynthetic capacity to influence HI. Further research found that the genes involved in circadian rhythms and response to stimulus may play important roles in HI and that their transcript levels were modulated by differentially expressed microRNAs (DEMs), and we identified 903 microRNAs (miRNAs), including 46 known miRNAs and 857 novel miRNAs. Furthermore, transporter activity-related genes were critical to enhancing HI in good cultivation environments. Of 903 miRNAs, we found that the bna-miR396–Bna.A06SRp34a/Bna.A01EMB3119 pair may control the seed development and the accumulation of storage compounds, thus contributing to higher HI. Our findings uncovered the underlying complex regulatory network behind HI and offer potential approaches to rapeseed improvement.
... Traits that contribute to improved soybean yield include longer reproductive or seed-filling periods (Gay et al., 1980;Kumudini et al., 2001;Shen and Liu, 2015), decreased lodging (Specht and Williams, 1984), and improved disease resistance (Foulkes et al., 2009). Changes in management practices that increased soybean yields are related to narrow rows (Heatherly and Elmore, 2004), improvement of weed control (Pike et al., 1991;Osteen, 1993;Bradley and Sweets, 2008), conservation tillage and reduction in harvest losses (Heatherly and Elmore, 2004), and early sowing (Wilcox and Frankenberger, 1987;Conley and Santini, 2007;Bastidas et al., 2008;Sacks and Kucharik, 2011). ...
... HI has shown a positive correlation with YD as previously documented in different studies (Yang and Zhang 2010;Duan et al. 2018;Porker et al. 2020). The positive association between yield and HI could be of major significance in encouraging breeders in their exploration for increased yield in wheat varieties (Foulkes et al. 2009;Aranjuelo et al. 2013;Duan et al. 2018). ...
1BL/1RS translocation is widely used around the world to enhance wheat yield potential, resistance to various diseases, and adaptation. However, the translocation is combined with inherent quality problems associated with reduced dough strength and dough stickiness due to the presence of Sec-1 on proximal end and absence of GluB3/GliB1 on distal end. Two NILs, one carrying the distal (1RSRW) and the other carrying the proximal (1RSWR) fragment from 1BS, in background of Pavon were used for transferring these two loci in yellow rust resistant version of two elite wheat varieties PBW550+Yr5 and DBW17+Yr5. Foreground and background marker assisted selection was done for the Sec-1- and GluB3+ alongwith Lr26/Yr9/Sr31, Pm8 and 1RS loci in the advancing generation. BC2F5:6 NILs with absence of Secalin and presence of GluB3/GliB1 loci were evaluated for two years in replicated yield trial. A positive correlation of thousand grain weight (TGW), harvest index (HI), and tiller number per meter (TNpM) with yield (YD) with significant GxE effect was observed. Further multivariate analysis of these traits contributed maximum to the effective yield. Thirty promising NILs were identified with Sec-1-/GluB3+ alongwith with high yield contributing parameters.
... Increasing wheat yield is therefore crucial to ensure global food security [14,15]. Current evidence indicates that wheat yield under favourable conditions is mainly limited by sink strength [1,20]. Analysis of breeding history also revealed wheat grain yield improvement ...
Background
Wheat spike architecture is a key determinant of multiple grain yield components and detailed examination of spike morphometric traits is beneficial to explain wheat grain yield and the effects of differing agronomy and genetics. However, quantification of spike morphometric traits has been very limited because it relies on time-consuming manual measurements.
Results
In this study, using X-ray Computed Tomography imaging, we proposed a method to efficiently detect the 3D architecture of wheat spikes and component spikelets by clustering grains based on their Euclidean distance and relative positions. Morphometric characteristics of wheat spikelets and grains, e.g., number, size and spatial distribution along the spike can be determined. Two commercial wheat cultivars, one old, Maris Widgeon, and one modern, Siskin, were studied as examples. The average grain volume of Maris Widgeon and Siskin did not differ, but Siskin had more grains per spike and therefore greater total grain volume per spike. The spike length and spikelet number were not statistically different between the two cultivars. However, Siskin had a higher spikelet density (number of spikelets per unit spike length), with more grains and greater grain volume per spikelet than Maris Widgeon. Spatial distribution analysis revealed the number of grains, the average grain volume and the total grain volume of individual spikelets varied along the spike. Siskin had more grains and greater grain volumes per spikelet from spikelet 6, but not spikelet 1–5, compared with Maris Widgeon. The distribution of average grain volume along the spike was similar for the two wheat cultivars.
Conclusion
The proposed method can efficiently extract spike, spikelet and grain morphometric traits of different wheat cultivars, which can contribute to a more detailed understanding of the sink of wheat grain yield.
... The Green Revolution in the 1960s and 1970s that produced the semi-dwarf cultivars (Conway, 1997) reduced the leverage on the stem base and anchorage system in wheat (Triticum aestivum L.) plants, thereby increasing the lodging resistance (Berry et al., 2004). Since then wheat yields have increased in breeding programs worldwide (Crespo-Herrera et al., 2017;Fischer et al., 2014;Foulkes et al., 2009;Gerard et al., 2020;Lopes et al., 2012;Tadesse et al., 2019), either with no further change in plant height or with increased plant height (Aisawi et al., 2015), and this has contributed to increased shoot and plant leverage. Therefore, reducing lodging in wheat remains an important strategy to maintain high yields and grain quality, especially in high-yielding environments. ...
Lodging affects grain quality and grain yield in wheat (Triticum aestivum L.) and is difficult to breed for because its sporadic incidence and laborious protocols to measure lodging traits. Thus, developing molecular markers for these traits can increase selection efficiency in breeding programs. The aim of this article is to identify quantitative trait loci (QTL) associated with stem/anchorage strength and leverage traits (lodging traits) in a doubled‐haploid population of UK bread wheat Avalon × Cadenza. Field experiments were conducted in the UK during 2012–2013 near High Mowthorpe and during 2013–2014 at Sutton Bonington. Phenotypic and genetic analysis indicated significant genetic variation for all traits. Stem strength (diameter, wall width, and material strength) and leverage (plant height) traits were highly heritable (0.64–0.95), whereas anchorage strength traits (root plate spread and structural rooting depth) and ear number per plant (leverage trait) were less heritable (0.21–0.33). This study identified 18 QTL for lodging traits and grain yield in chromosomes 1D, 2B, 2D, 3A, 3B, 4A, 4D, 5B, and 6B. Two QTL for stem strength on chromosome 1D and 3B explaining 49.6% of the total phenotypic variation (PVE) are estimated to reduce stem lodging risk and shortening the plant height by 12 cm. One QTL for root plate spread on chromosome 5B explaining 22.4% of the PVE could increase root lodging resistance.
... Current evidence indicates that wheat yield under favourable conditions is mainly limited by sink strength (Foulkes et al., 2009;Zhang et al., 2010). Analysis of breeding history also revealed wheat grain yield improvement in the last century was highly associated with increase in grain number per unit area, which is largely determined by the grain number per spike (Hawkesford et al., 2013). ...
Background: Wheat spike architecture is a key determinant of multiple grain yield components and detailed examination of spike morphometric traits is beneficial to explain wheat grain yield and the effects of differing agronomy and genetics. However, quantification of spike morphometric traits has been very limited because it relies on time-consuming manual measurements.
Results: In this study, using X-ray Computed Tomography imaging, we proposed a method to efficiently detect the 3D architecture of wheat spikes and component spikelets by clustering grains based on their Euclidean distance and relative positions. Morphometric characteristics of wheat spikelets and grains, e.g., number, size and spatial distribution along the spike can be determined. Two commercial wheat cultivars, one old, Maris Widgeon, and one modern, Siskin, were studied as examples. The average grain volume of Maris Widgeon and Siskin did not differ, but Siskin had more grains per spike and therefore greater total grain volume per spike. The spike length and spikelet number were not statistically different between the two cultivars. However, Siskin had a higher spikelet density (number of spikelets per unit spike length), with more grains and greater grain volume per spikelet than Maris Widgeon. Spatial distribution analysis revealed the number of grains, the average grain volume and the total grain volume of individual spikelets varied along the spike. Siskin had more grains and greater grain volumes per spikelet from spikelet 6, but not spikelet 1-5, compared with Maris Widgeon. The distribution of average grain volume along the spike was similar for the two wheat cultivars.
Conclusion: The proposed method can efficiently extract spike, spikelet and grain morphometric traits of different wheat cultivars, which can contribute to a more detailed understanding of the sink of wheat grain yield.
... Increasing wheat yield is therefore crucial to ensure global food security (Senapati et al., 2019;Senapati and Semenov, 2020). Current evidence indicates that wheat yield under favourable conditions is mainly limited by sink strength (Foulkes et al., 2009;Zhang et al., 2010). Analysis of breeding history also revealed wheat grain yield improvement in the last century was highly associated with increase in grain number per unit area, which is largely determined by the grain number per spike (Hawkesford et al., 2013). ...
Background
Wheat spike architecture is a key determinant of multiple grain yield components and detailed examination of spike morphometric traits is beneficial to explain wheat grain yield and the effects of differing agronomy and genetics. However, quantification of spike morphometric traits has been very limited because it relies on time-consuming manual measurements. ResultsIn this study, using X-ray Computed Tomography imaging, we proposed a method to automatically and efficiently detect the 3D architecture of wheat spikes and component spikelets by clustering grains based on their Euclidean distance and relative positions. Morphometric characteristics of wheat spikelets and grains, e.g. number, size and spatial distribution along the spike can be automatically determined. Two commercial wheat cultivars, one old, Maris Widgeon, and one modern, Siskin, were studied as examples. The average grain volume of Maris Widgeon and Siskin did not differ, but Siskin had more grains per spike and therefore greater total grain volume per spike. The spike length and spikelet number were not statistically different between the two cultivars. However, Siskin had a higher spikelet density (number of spikelets per unit spike length), with more grains and greater grain volume per spikelet than Maris Widgeon. Spatial distribution analysis revealed the number of grains, the average grain volume and the total grain volume of individual spikelets varied along the spike. Siskin had more grains and greater grain volumes per spikelet from spikelet 6, but not spikelet 1-5, compared with Maris Widgeon. The distribution of average grain volume along the spike was similar for the two wheat cultivars. Conclusion
The proposed method can automatically and efficiently extract spike, spikelet and grain morphometric traits of different wheat cultivars, which can contribute to a more detailed understanding of the sink of wheat grain yield.
... HI and RUE are the most important parameters for predicting crop yield [11]. Increase in HI has been the main target of enhancing grain yield in wheat since the 1960s [31], which increased from 35% in 1951-1955 to 50% in 1995-2013 [32][33][34], and could reach a maximal value of 62% [35] in modern winter wheat. In the present study, HI ranged between 42% and 50% and was significantly greater for plants grown on clay soil than on sandy soil and with high N-fertilization level than with low N-fertilization level. ...
There is an urgent need among plant breeders for a deeper understanding of the links between wheat genotypes and their ability to utilize light for biomass production and their efficiency at converting the biomass into grain yield. This field trail was conducted to investigate the variations in radiation use efficiency (RUE) and harvest index (HI) of four spring wheat cultivars grown on two soil types with two nitrogen (N) fertilization levels. Grain yield (GY) was significantly higher with 200 kg N ha −1 than 100 kg N ha −1 and on clay soil than on sandy soil, and a similar trend was observed for shoot dry matter (DM) at maturity. RUE and HI was neither affected by cultivar nor N-fertilization, but was affected by soil type, with a significantly higher RUE and HI on clay than on sandy soil. The differences of water holding capacity between the two soil types was suggested to be a major factor influencing RUE and HI as exemplified by the principal component analysis. Thus, to achieve a high RUE and/or HI, sustaining a good soil water status during the critical growth stages of wheat crops is essential, especially on sandy soils with a low water holding capacity.
... While, Nitrogen Utilization Efficiency (NUE) is ratio of grain mass and plant (or shoot) N content (NUE) is estimated at about 33%, with NUE's of 42 and 29% in developed and developing countries (Raun and Johnson 1999). There is scope to improve the NUE within adapted germplasm by up to 20% (Foulkes et al., 2009). As a Plant breeder must produce varieties that absorb N more efficiently and use it more efficiently to produce biomass. ...
Biochips: An Overview of miniaturized Laboratories
... Compared with old cultivars, GN is the main driving force for increasing grain yield in new cultivars [47]. GN at each of the four grain positions contributed to the increased of total grain number per area. ...
Grain number and weight within a spikelet are major yield components which determine the grain yield in wheat. The objective of this study was to explore genetic gains in grain performance within wheat spikelets at the individual grain level and its effect on grain yield and evaluate genetic progress in stem internode length and other yield-related traits. We conducted field experiments across three growing seasons in the western Yellow and Huai Valley of China; incorporating 17 bread wheat cultivars released from 1948 to 2012. Yields were significantly correlated with year of release. Yield gains equated to 3.95 g m−2 yr−1 in response to increases in total grain weight per m2 (GW) in proximal (G1 and G2) and distal (G3 and G4) grains, despite a decline in the proportional contribution of proximal grains to yield and increase in the proportional contribution of distal grains to yield with year of release. Grain number per m2 (GN), thousand-grain weight (TGW), and harvest index (HI) increased with year of release, but plant height decreased. Both grain number per spikelet of proximal and distal grain contributed to the increase in total GN. However, the contribution ratio of GN in proximal grains to total GN declined, and the proportion in distal grains increased. Average single grain weight (SGW) increased linearly at G1, G2, G3, and G4 with year of release and contributed to the increase in TGW. The G3 and G4 grain positions had much lower individual grain weights but increased at a faster rate than G1 and G2. At G1, G2, and G3 grain positions, from bottom to top spikelets, the newly released cultivars had the heaviest grains and the old cultivars had the lightest grains. New cultivars had more spikelets than old cultivars and the number of grains (proximal and distal grains) in the apical spike increased with year of release. The length of five internodes decreased significantly with year of release, more so in the upper than lower internodes, all of which contributed to the decline in plant height. In summary, increasing the number and weight of distal grains could increase grain yield, TGW, and GN.
... The results are consistent with the findings showing an increased number of grains per spike in modern German cultivars (Würschum et al., 2018). Several other studies also identified grains per spike as the trait with the closest relationship to yield progress in other regional cultivar collections (Brancourt-Hulmel et al., 2003;Acreche et al., 2008;Foulkes et al., 2009;Sanchez-Garcia et al., 2013). This implies that breeding progress has been achieved predominantly by increasing sink size. ...
Optimizing the interplay between sinks and sources is of crucial importance for breeding progress in winter wheat. However, the physiological limitations of yield from source (e.g. green canopy duration, GCD) and sink (e.g. grain number) are still unclear. Furthermore, there is little information on how the source traits have been modified during the breeding history of winter wheat. This study analyzed the breeding progress of sink and source components and their relationships to yield components. Field trials were conducted over three years with 220 cultivars representing the German breeding history of the past five decades. In addition, genetic associations of QTL for the traits were assessed with genome-wide association studies. Breeding progress mainly resulted from an increase in grain numbers per spike, a sink component, whose variations were largely explained by the photosynthetic activity around anthesis, a source component. Surprisingly, despite significant breeding progress in GCD and other source components, they showed no direct influence on thousand grain weights, indicating that grain filling was not limited by the source strength. Our results suggest that, 1) the potential longevity of the green canopy is predetermined at the time point that the number of grains is fixed; 2) a co-evolution of source and sink strength during the breeding history contribute to the yield formation of the modern cultivars. For future breeding we suggest to choose parental lines with high grain numbers per spike on the sink side, and high photosynthetic activity around anthesis and canopy duration on the source side, and to place emphasis on these traits throughout selection.
... On the other hand, Abeledo et al (2004) reported that variation in PHY was associated with YCR, while changes in FLN were not related to YCR in malting barley. Nevertheless, shorter PHY and increased FLN could be related to early vigour, leading to accelerated canopy closure, reduced evapotranspiration and improved radiation interception ( Foulkes et al. 2009). Therefore, a further PHY decrease, followed by increase in FLN, could be relevant during early growth stages in environments characterized by adverse weather conditions, especially for spring small-grain barley. ...
The aim of this study was to analyze traits of leaf appearance and phenological development related to grain yield gain in winter barley cultivars released over the past 50 years. Field trials with 15 six-rowed winter barley cultivars were conducted during two growing seasons. The main leaf appearance and developmental traits were studied. The duration of the emergence-anthesis and emergence-physiological maturity phases decreased by 2.35 and 2.16 GDD yr-1, respectively. The duration of the stem elongation-anthesis phase was 10% longer in modern cultivars. The results showed no clear trend of improvement in final leaf number and phyllochron. The duration of the stem elongation-anthesis phase was positively related with grain number and yield. Constant improvements in grain number and grain weight by fine manipulation of the crop developmental phases could represent an essential strategy for further increases in barley grain yield potential.
... Because grain number is strongly correlated to the stem and/or spike dry weight at flowering (Slafer et al., 1990;González et al., 2005;Beche et al., 2014), greater aboveground biomass before or around anthesis of higher early vigour wheat significantly increased grain number per unit area as compared with baseline scenario. Our modelling results show that the contribution of early vigour to yield increase is largely through increased grain number rather than grain size, similar to contributions of other yieldincreasing traits (Foulkes et al., 2009). In wetter years or sites, this increased number of grain will have better chance to be filled, leading to more yield benefits. ...
Early vigour, or faster early leaf area development, has been considered an important trait for rainfed wheat in dryland regions such as Australia. However, early vigour is a genetically complex trait, and results from field experiments have been highly variable. Whether early vigour can lead to improved water use efficiency and crop yields is strongly dependent on climate and management conditions across the entire growing season. Here, we present a modelling framework for simulating the impact of early vigour on wheat growth and yield at eight sites representing the major climate types in Australia. On a typical soil with plant available water capacity (PAWC) of 147 mm, simulated yield increase with early vigour associated with larger seed size was on average 4% higher compared with normal vigour wheat. Early vigour through selection of doubled early leaf sizes could increase yield by 16%. Increase in yield was mainly from increase in biomass and grain number, and was reduced at sites with seasonal rainfall plus initial soil water <300 mm. Opportunities exists for development of early vigour wheat varieties for wetter sites. Soil PAWC could play a significant role in delivering the benefit of early vigour and would require particular attention.
... Among relevant management practices to be highlighted are earlier planting dates (Conley and Santini, 2007;Bastidas et al., 2008), use of conservation tillage, narrow row spacing, reduction of harvest losses (Heatherly and Elmore, 2004), and improvement in weed control (Bradley and Sweets, 2008). On the other hand, reported genetic improvements in plant traits are related to disease resistance (Foulkes et al., 2009), longer seed filling (Gay et al., 1980), shorter vegetative period favoring longer reproductive periods (Shen and Liu, 2015), and a reduction in lodging (Specht and Williams, 1984). Balboa et al. (2018) summarized that soybean yield improvements (from 1922 to 2015), primarily impacting biomass production, resulted from both fine-tuning management practices and advances in genetics. ...
Yields (seed number) increased over time with modern soybean genotypes.
Seed protein concentration decreased over time.
Nitrogen fertilization impacted yield via changes on the seed weight.
Nitrogen limited yields for high‐yielding modern soybean genotypes.
The United States (USA) and Argentina (ARG) account for over 50% of the global soybean [ Glycine max (L.) Merr.] production. Soybean N demand is partially met (50–60%) by the biological nitrogen fixation (BNF) process; however, an unanswered scientific knowledge gap exists on the ability of the BNF process to fulfill soybean N demand at varying yield levels. The overall objective of this study is to explore the potential N limitation using different N strategies for historical and modern soybean genotypes. Four field experiments were conducted during 2016 and 2017 growing seasons in Kansas (USA) and Santa Fe (ARG). Twenty‐one historical and modern soybean genotypes released from the 1980s to 2010s were tested under three N treatments: (i) control, without N application (Zero‐N); (ii) 56 kg N ha ⁻¹ applied at R3‐R4 growth stages (Late‐N); and (iii) 670 kg ha ⁻¹ equally split at planting, R1, and R3–R4 growth stages (Full‐N). Historical soybean yield gains, from the 1980s to 2010s, were 29% in the USA and 21% in ARG. Following the yield trend, seed N content increased for modern genotypes in parallel to the reduction on seed protein concentration. Regarding N treatments, Full‐N produced 12% yield increase in the USA and 4% in ARG. Yield improvement was mainly related to increases in aboveground biomass, seed number (genotype effect), and to a lesser extent, to seed weight (N effect). This study suggests a potential N limitation for soybean, although there are still questions about the way in which N must be provided to the plant.
... Among relevant management practices to be highlighted are earlier planting dates (Conley and Santini, 2007;Bastidas et al., 2008), use of conservation tillage, narrow row spacing, reduction of harvest losses (Heatherly and Elmore, 2004), and improvement in weed control (Bradley and Sweets, 2008). On the other hand, reported genetic improvements in plant traits are related to disease resistance (Foulkes et al., 2009), longer seed filling (Gay et al., 1980), shorter vegetative period favoring longer reproductive periods (Shen and Liu, 2015), and a reduction in lodging (Specht and Williams, 1984). Balboa et al. (2018) summarized that soybean yield improvements (from 1922 to 2015), primarily impacting biomass production, resulted from both fine-tuning management practices and advances in genetics. ...
... Yield potential is usually represented as a function of its numerical yield components, grain number, and grain weight (Fischer et al. 2014). No significant correlations were observed between grain number per unit area with yield for the subset of 27 lines, even though grains per unit area is the component considered most closely correlated with grain yield (Slafer et al. 1994;Fischer 2008;Foulkes et al. 2009). However, when the analysis was restricted to only the 22 hexaploid elite lines, a correlation among yield and GNO was obtained, indicating that part of the genetic gains of the historical material were related with TGW. ...
... A major part of future of breeding for greater PY relates to those yield-enhancing plant and crop traits still amenable to change through breeding. This has been widely discussed by crop physiologists (e.g., Foulkes et al., 2009;Reynolds and Langridge, 2016) and in Fischer et al. (2014). Greatest emphasis is currently being placed on increasing carbon gain (biomass) through increasing leaf and canopy photosynthesis, and hence crop radiation-use efficiency. ...
... In the last five decades, genetic gains in common and durum wheat have been mainly obtained by increasing harvest index associated to the gradual reduction in plant height. Further improvement are expected by increasing the biomass production and the radiation use efficiency without any reduction of the harvest index of modern cultivars [7][8][9][10]. Anyway, grain yield potential is the final product of plant growth and development, and several others complex factors, such as abiotic stress tolerance, adaptation to different soils and climate changes, disease resistances, contribute to plant productivity. ...
Increasing grain yield potential in wheat has been a major target of most breeding programs. Genetic advance has been frequently hindered by negative correlations among yield components that have been often observed in segregant populations and germplasm collections. A tetraploid wheat collection was evaluated in seven environments and genotyped with a 90K SNP assay to identify major and stable quantitative trait loci (QTL) for grain yield per spike (GYS), kernel number per spike (KNS) and thousand-kernel weight (TKW), and to analyse the genetic relationships between the yield components at QTL level. The genome-wide association analysis detected eight, eleven and ten QTL for KNS, TKW and GYS, respectively, significant in at least three environments or two environments and the mean across environments. Most of the QTL for TKW and KNS were found located in different marker intervals, indicating that they are genetically controlled independently by each other. Out of eight KNS QTL, three were associated to significant increases of GYS, while the increased grain number of five additional QTL was completely or partially compensated by decreases in grain weight, thus producing no or reduced effects on GYS. Similarly, four consistent and five suggestive TKW QTL resulted in visible increase of GYS, while seven additional QTL were associated to reduced effects in grain number and no effects on GYS. Our results showed that QTL analysis for detecting TKW or KNS alleles useful for improving grain yield potential should consider the pleiotropic effects of the QTL or the association to other QTLs.
... Traits that contribute to improved soybean yield include longer reproductive or seed-filling periods (Gay et al., 1980;Kumudini et al., 2001;Shen and Liu, 2015), decreased lodging (Specht and Williams, 1984), and improved disease resistance (Foulkes et al., 2009). Changes in management practices that increased soybean yields are related to narrow rows (Heatherly and Elmore, 2004), improvement of weed control (Pike et al., 1991;Osteen, 1993;Bradley and Sweets, 2008), conservation tillage and reduction in harvest losses (Heatherly and Elmore, 2004), and early sowing (Wilcox and Frankenberger, 1987;Conley and Santini, 2007;Bastidas et al., 2008;Sacks and Kucharik, 2011). ...
Few studies have investigated changes over time in nutrient uptake and yield, in addition to the study of nutrient stoichiometry as a metric of nutrient limitations in soybean [Glycine max (L.) Merr.]. A comprehensive synthesisanalysis was performed by compiling a global historical soybean database of yield, total biomass, and nutrient (N, P, and K) content and concentration in studies published from 1922 to 2015. This period was divided in three eras based on genetically modified soybean events: Era I (1922-1996), Era II (1997-2006), and Era III (2007-2015). The main findings of this review are: (i) seed yield improved from 1.3 Mg ha⁻¹ in the 1930s to 3.2 Mg ha⁻¹ in the 2010s; (ii) yield increase was primarily driven by increase in biomass rather than harvest index (HI); (iii) both N and P HIs increased over time; (iv) seed nutrient concentration remained stable for N and declined for both P (18%) and K (13%); (v) stover nutrient concentration remained stable for N, diminished for P, and increased for K; (vi) nutrient ratios portray different trends for N/P (Era I and III > II), N/K (Era I > II and III), and K/P (Era II and III > I); (vii) yield per unit of nutrient uptake (internal efficiency) increased for N (33%) and P (44%) and decreased for K (11%); and (viii) variations in nutrient internal efficiency were primarily explained by increase in nutrient HI for N and K, but equally explained by both HI for P and seed P concentration. These findings have implications for soybean production and integrated nutrient management to improve yield, nutrient use efficiency, and seed nutrient composition.
... Grain number per unit area was the main driver of grain yield increments in modern cultivars compared to old ones (Foulkes et al., 2009). The trends found in genetic progress evaluated through grain yield or grain number are different between different countries. ...
The objective of this study is to update the data of genetic progress in bread wheat cultivars released in Argentina from 1918 to 2011 (emphasizing the last 20 years) characterizing different agronomic traits of interest for breeders. Experiments were carried out with a wide range of bread wheat cultivars and conducted under field conditions without nutritional and water restrictions. Yields showed a significant (R² =0.68) tri-linear trend when associated with the cultivar's year of release. Until the 40s, when the first inflection point occurred, the genetic progress in terms of yield was 0.8kgha⁻¹ yr⁻¹ (0.02% yr⁻¹). Between 1940 and 1999, yield genetic progress reached its highest value (51kgha⁻¹ yr⁻¹; 1.17% yr⁻¹) but changed after 1999 when values became lower compared to the previous period, showing a value of 14kgha⁻¹ yr⁻¹ (0.18% yr⁻¹). Changes in grain yield were mostly explained by increases in harvest index and not by those in above-ground biomass. Plant height showed a negative bi-linear trend with the year of release, reaching an inflexion point well before the introgression of semi-dwarfing genes in commercial cultivars. Grain number increased ca. 63% when modern cultivars were compared to older ones, which explains most of the grain yield changes. In contrast to grain number, no significant differences between old and modern cultivars were found for grain weight, with average values of ca. 30mggrain⁻¹ for all environments explored.
... Wheat (Triticum aestivum L.) is the most widely grown cereal crop. The primary objective of most breeding programs is the development of high-yielding genotypes and improvement of grain yield potential (Foulkes et al., 2009). Since the Green Revolution, wheat yields have increased in many regions of the world (Gewin, 2010). ...
To determine root growth and grain yield of winter wheat (Triticum aestivum L) under moderate drought stress, a nursery experiment and a field trial were conducted with or without water stress using three representative cultivars released in different years: CW134 (old landrace), CH58 (modern cultivar) and CH1 (new release). In the nursery experiment, plants were grown in soil-filled rhizoboxes under moderate drought (MD, 55% of field capacity) or well-watered (WW, 85% of field capacity) conditions. In the field trial, plots were either rainfed (moderate drought stress) or irrigated with 30 mm of water at each of stem elongation, booting and anthesis stages (irrigated). Compared to drought stress, grain yields increased under sufficient water supply in all cultivars, particular the newly released cultivar CH1 with 70% increase in the nursery and 23% in the field. When well-watered (nursery) or irrigated (field), CH1 had the highest grain yields compared to the other two cultivars, but produced similar yield to the modern cultivar (CH58) under water-stressed (nursery) or rainfed (field) conditions. When exposed to drought stress, CW134 had the highest topsoil root dry mass in topsoil but lowest in subsoil among the cultivars at stem elongation, anthesis, and maturity, respectively; while CH1 had the lowest topsoil and highest subsoil root dry mass at respective sampling times. Topsoil root mass and root length density were negatively correlated with grain yield for the two water treatments in nursery experiment. When water was limited, subsoil root mass was positively correlated with thousand kernel weight (TKW). In the field trial, CH1 and CH58 used less water during vegetative growth than CW134, but after anthesis stage, CH1 used more water than the other two cultivars, especially in the soil profile below 100 cm, which was associated with the increased TKW. This study demonstrated that greater root mass and root length density in subsoil layers, with enhanced access to subsoil water after anthesis, contribute to high grain yield when soil water is scarce.
... It has been shown that leaf erectness is an important trait in breeding for radiation use efficiency and there has been considerable success in breeding for more erect canopies in both rice and wheat (Yunusa et al., 1993;Sinclair and Muchow, 1999;Foulkes et al., 2009). The available genetic variation in this trait raises the question of the requirement to engineer erectness. ...
Since the ground breaking work of Norman Borlaug in the 1960s produced large increases in yields of our major cereal crops, we have seen a gradual decline in annual yield progress. The genetic potential of the yield components harvest index and grain number, which were targeted in the “green revolution” and subsequently by cereal breeders have largely been optimised in our two largest global cereal crops, rice and wheat. Physiologists and breeders are turning to the biomass portion of the yield equation and in particular radiation use efficiency, as a means to push the yield potential barrier. Consequently, in the last decade a large effort has been initiated to identify targets to improve photosynthetic performance both using non-transgenic Phenomics approaches and transgenic technologies. Efficiency of light interception, harvesting and energy utilisation have been targeted but most efforts have so far focussed on improving photosynthetic capacity and efficiency in photosynthetic carbon metabolism in rice, wheat and model plants. Here the targets for improving light harvesting and carbon fixation are reviewed, the progress thus far evaluated and the likelihood of success of these activities in improving crop yields discussed in the context of modelling and scaling from the leaf to the canopy.
... First, the techniques used to raise potential yields -that is, the yield achievable on the best land in good conditions -produced a one-time gain. Even including new techniques, such as genetic modification of plants, future yield increases are expected to be smaller and harder to achieve than in the past, at least for grains (Foulkes et al. 2009). Second, the environmental impact of agriculture -along with other human activities -is exceeding a "safe operating space" for humanity (Rockström et al. 2009;Zalasiewicz et al. 2008). ...
... Semi-dwarf cultivars introduced in the 1960s and 1970s contributed large increases in GN associated with more fertile florets per spike as a consequence of increased assimilate partitioning to the spike during the pre-flowering period (Fischer, 1983). Since then, there have been continued improvements in both GN and HI in breeding programs worldwide (Reynolds et al., 1999;Foulkes et al., 2009;Peltonen-Sainio et al., 2009;Reynolds et al., 2011Reynolds et al., , 2012Clarke et al., 2012). ...
Abstract
The production of oilseeds, edible leaves, and secondary metabolites of dragon's
head makes it an important food, forage, and medicinal plant. Choosing a proper
planting date and plant nutrition can make a significant effect on crop plants growth,
quality and yield.The effects of planting date (16 March, 14 April, and 13 May 2019)
and foliar application of zinc sulfate (zero as control, 2 and 4 g.L-1 ) on growth indices and seed yield of dragon's head was evaluated under a field experiment. Delayed planting date reduced the days to flowering, days to seed ripening, plant height, leaf area index (LAI), crop growth rate (CGR), relative growth rate (RGR) and grain yield, and yield components.In contrast, the use of zinc sulfate increased plant height, LAI, CGR and RGR. There was a correlation between plant height and number of branches and consequently there were more capsules per plant.The highest effect of zinc sulfate application on seed yield and yield components was observed in the first planting date and with delay in planting, the efficiency of zinc sulfate fertilizer application decreased. On the third planting date, zinc sulfate application had no significant effect on grain yield. As a result of late planting, fewer branches, fewer capsules per plant, and smaller seeds contributed to the yield reduction.It was found that early cultivation and application of zinc sulfate increased plant height, number of branches, number of capsules per plant, 1000-seed weight, and thus seed yield, by increasing the days to flowering, days to ripening, LAI, CGR, and RGR.
Breeding and selection for harvest index to improve yield potentials have reached its biological ceiling limit. Recent efforts are on increasing yield potential by increasing biomass by optimizing radiation use efficiency (RUE). RUE is the efficiency of biomass production per unit light captured. It is essential to increase yield to meet the food demand of the growing population that is dependent on diminishing arable land. Improvements in RUE are possible by increasing photosynthetic efficiencies and its capacity. In this chapter, we describe the current understanding on RUE, the avenues that can be explored at leaf and canopy level to increase or optimize RUE, with major emphasis on improving photosynthetic efficiencies are discussed in detail.KeywordsRadiation use efficiencyNonphotochemical quenchingPhotorespirationRubiscoSmart canopy
Investigating the relationship between grain yield and main agronomic traits and understanding the trend of changes in traits during breeding history are important for breeding strategies. In order to determine the trend of changes in improved wheat cultivars and calculate the genetic gain of yield and related traits, 20 spring wheat cultivars released for the northern climate of the Iran during the years 1968 to 2018 were evaluated. Cultivars were cultivated in a randomized complete block design with three replications in Gorgan, Gonbad, Sari and Moghan in three consecutive years (2015–18). Morphological and phenological traits and grain yield and related traits were assessed in each year. Linear regression analysis between investigated characteristics and year of cultivar release showed that the grain yield, biological yield, harvest index, number of spikes per square meter, thousand-kernel weight and grain filling rate were significantly increased. No significant changes, however, were observed during breeding programs in maturity-related traits such as days to heading, days to anthesis, days to maturity, duration of grain filling, plant height, peduncle length, spike length and number of grains per spike. According to the positive and significant correlation between biomass, harvest index, number of spikes per square meter and thousand-kernel weight with grain yield, it seems that breeders in the northern climate of the country have been selected these traits to increase grain yield during the process of breeding cultivars.
Knowledge about the yield gain over the years due to associated changes in the yield component traits is essential for a critical understanding of yield-limiting factors. To estimate genetic gain in grain yield (GY) and component agronomic traits of wheat varieties released between 1900 and 2016 for northwestern plain zone (NWPZ) of India and to identify agronomic and/or genetic basis of the realized gains, two sets of wheat varieties comprising mega varieties and two recently developed varieties were evaluated under timely sown, tilled, and early sown conservation agriculture (CA) conditions for four consecutive years under irrigated conditions. The average annual genetic gain in GY since 1,905 under timely sown irrigated conditions was found to be 0.544% yr⁻¹ over the average of all varieties and 0.822% yr⁻¹ (24.27 kg ha⁻¹ yr⁻¹) over the first released variety, NP4. The realized mean yield increased from 2,950 kg ha⁻¹ of the variety NP4 released in 1,905–5,649 kg ha⁻¹ of HD3086 released in 2014. Regression analysis revealed a linear reduction in height and peduncle length (PL) over the years with a simultaneous and linear increase in biomass at the rate of 43.9 kg ha⁻¹ yr⁻¹ or relatively at 0.368% yr⁻¹ mainly because of delayed heading and increased crop duration. Regression analysis showed no linear trend for tiller number and thousand-grain weight (TGW). Though harvest index (HI) was found to linearly increase relatively at the rate of 0.198% per annum, polynomial regression improved the fitness of data with the indication of no increase in HI since 1982. Interestingly, genetic gain evaluation under early sown CA conditions for 4 years showed similar relative gain (RG) [a relative improvement in varieties across breeding periods (BP)] (0.544% yr⁻¹) but with a higher absolute value (29.28 kg ha⁻¹ yr⁻¹). Major mega varieties like Kalyan Sona, HD2009, PBW 343, HD2967, and HD3086, which occupied a comparatively larger area, were found highly plastic to the improvements in the production environment under timely sown conditions.
At global level nitrogen (N) fertilizers had drastic effects on crop yields increment during the last century. However, high application rates of this input have resulted to environmental pollution all around the world in addition decreased yields per unit of applied N is also reported in some countries. To fulfill increasing demands for agricultural crops with conservative application of N fertilizers, increasing N use efficiencies is recognized as a sustainable management. This calls for systematic studies on N use efficiency and its components at crop, field and regional levels. However, N efficiencies of agricultural crops at national level are not fully analyzed in Iran. In this research, forty years (1960-2010) data on yield and N application rate were analyzed for yield trend, N efficiencies and its related components for wheat (Triticum aestivum L.) production systems of Iran.
Required data of wheat yield and nitrogen fertilizer application rates during the 40 years study period was obtained from official web sites of national agricultural statistics as well as Ministry of Jihad Agriculture. Using these data partial nitrogen productivity (kg yield kg N-1); nitrogen use efficiency (kg yield kg-1 N, ignoring soil N), nitrogen uptake efficiency (%); nitrogen utilization efficiency (kg yield kg-1 absorbed N); and relative contribution of Nitrogen to grain yield (%) was estimated based on previously reported methods. Yield and N fertilizer application rate were subjected to time series analysis and fertilizer rates were predicted for the next decade over the studied period.
The results indicated that during the studied period mean annual growth rate of wheat yield and nitrogen application were 2.9 and 6.9%, respectively leading to 3.4 fold increase in yield and 9.5 fold increase in N fertilizers so that fertilize application rate was changed from 25 to 240 kg ha-1. However, N fertilizer application rate in wheat production systems of Iran is reducing since 80’s and prediction based on time series indicted that this rate will not exceed 250 kg ha-1 by 2020. Partial N productivity was estimated as 22.5 kg grain .kg-1 applied N which is reduced linearly over the studied period with the slope of -0.19 kg ha-1.y-1. Mean N use efficiency (NUE) in wheat production systems over the country averaged over four studied decades was 14.5 kg grain kg-1 applied N. Separation of NUE to its components showed that on average 35.5% of applied N was recovered in wheat agroecosystems of Iran and due decreasing trend of recovery N uptake efficiency was reached to 30% in the late 80’s. However, mean N utilization efficiency was estimated as 40 kg grain kg-1 absorbed N and increased slightly during the last four decades. Relative contribution of N fertilizers to wheat yield was increased with a positive slope from 24% in the first decade of the study period to 32% after 40 years. Based on the results it seems that the decreasing trend in NUE of wheat production systems of Iran is mainly due to low uptake efficiency which was not compensated for by slight improvement of N utilization efficiency.
Nitrogen application rate in wheat production systems of Iran has increased expansively during the last four decades. However, nitrogen uptake efficiency in wheat production systems of the country is considerably low and has resulted in a decreasing trend in nitrogen use efficiency over the last 40 years despite relative increase of N utilization efficiency over this period. Increasing N recovery through protecting N losses at field level, genetic improvement of N utilization efficiency and regulation of N fertilizers price compared to the price of wheat grain are urgent priorities to sustain wheat yield at national level with lower N application rates.
In wheat and other grain species, variations in kernel size are related to variations in ovary size. It is not known whether environmental factors that are known to affect kernel size may also affect ovary size, thus maintaining the kernel size-ovary size correlation. Additionally, it is not known whether variations in ovary size in wheat depend on cell size, cell number or both. In this study, ovary size was measured with a stereomicroscope, and ovary wall cell size and number were measured in equatorial cross-sectional areas of the ovary wall in two common wheat cultivars with different kernel size: Bora (large kernels) and Bologna (small kernels). Plants were grown at low and high N fertilization (0 and 240 kg ha⁻¹) with normal density (450 seeds m⁻²), and at low and high plant density (200 and 650 plants m⁻²) with normal fertilization (160 kg N ha⁻¹). The variation in ovary wall size across all data pooled (i.e., including two genotypes, two N and two density treatments, and including within treatment variations), was related to cell number and not to the cell size, which did not vary significantly with cultivar and field practices. With increasing ovule size, ovary wall size increased less than proportionally, thus the ovule/ovary ratio increased. Cell size in the ovary wall showed an upper limit across all treatments, which decreased with increasing cell number. These findings may be useful for breeding programs and field practices aimed at increasing kernel size and yield. © Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA All rights reserved.
Atmospheric CO2 concentrations [CO2] are continually increasing and are predicted to reach ~550 μmol mol−1 by 2050, about a 40 % increase from 2013 levels. Such a large increase in one of the key resources for plant growth will have significant effects on all plants, as carbon assimilation and, consequently, growth and yield is stimulated by the so-called ‘CO2 fertilisation effect’. The one sided increase in carbohydrate acquisition leads to changes in the chemical composition of plants: despite decreases in nutrient concentrations in plant tissues, the greater biomass developed by crops under elevated [CO2] could lead to increased nutrient demand. Nutrient use efficiency in terms of yield divided by available nutrient may improve, but grains or vegetative plant parts have decreased protein and mineral nutrient concentrations, which can diminish market and nutritious value. A number of hypotheses have been proposed to explain the decreases in nutrient concentrations, among them: (1) Dilution by increased biomass, (2) decreased mass flow, (3) changes in root architecture and function, (4) decreased nitrate reduction, and (5) changes in nutrient allocation and remobilisation. In addition, elevated [CO2] is likely to change soil processes, including nutrient supply. The extent to which some or all of these contribute to changes in crop nutrition and yield quality is currently unknown because most have not been sufficiently tested under relevant field conditions. This chapter gives an overview of the changes in plant nutrition and trade-offs under elevated [CO2] to point out that current and future efforts towards improved plant nutrient efficiency should explicitly take into consideration rising [CO2]. In particular, field testing of putative nutrient use efficiency traits and nutrient management strategies should include elevated [CO2] as a relevant factor in suitable exposure systems such as Free Air CO2 Enrichment (FACE) technology.
Wheat (Triticum aestivum L.) breeding strategies can benefit from periodic evaluation of genetic gains for physiological and morphological traits, and their contribution to yield progress over time in a particular environment. The objective of this research was to expand the recent work at Virginia Tech on genetic yield improvement in soft red winter (SRW) wheat and determine the magnitude of progress for several physiological traits in 50 SRW wheat cultivars released from 1919 to 2009. Physiological traits evaluated here were extensively reported in the literature to be relevant for future wheat breeding as they directly contributed to yield increase under optimum and suboptimal environmental conditions; these traits include canopy temperature depression (CTD), flag leaf width (W), flag leaf area (LA), flag leaf dry weight (DW), flag leaf specific area (SLA), SPAD (soil plant analysis development) chlorophyll reading, and grain ¹³C isotope discrimination (Δ). Replicated experiments were performed at Warsaw and Holland, VA, in 2009–2010 and 2010–2011 growing seasons. Results showed that three traits consistently changed in magnitude over time and, at the same time, were significantly (p < 0.01) related to yield; they were LA, smaller leaf area-higher yields; DW, lighter leaves-higher yields; and Δ, higher Δ-higher yields. CTD decreased in magnitude and SLA, W, and SPAD chlorophyll reading did not significantly change over time. Our data suggest that further yield increase in the SRW wheat grown in eastern Unites States can be achieved through selection of cultivars with smaller leaves, and with high Δ.
The optimization of management practices for oats is hindered by a lack of knowledge of the critical phenological phases at which management should be focussed. The objective of the present review was to identify the yield-limiting phases in the growth of the oat crop in order to optimize management and to maximize yield. The methodology employed was to identify characteristics associated with either the pre-anthesis grain number determination phase or with the post-anthesis grain filling phase. Characteristics associated with the pre-anthesis phase were identified as a positive linear relationship between yield and grain number, in addition to insensitivity of grain weight to changes in assimilate supply. Characteristics associated with the post-anthesis grain filling phase were identified as an absence of a relationship between yield and sink size (grain number) and changes in grain weight in response to changes in assimilate supply. Data was taken from published literature. Yields of both winter- and spring-sown hulled oats increased linearly with grain number showing a strong influence of grain number on yield. Grain weight of both winter- and spring-hulled oats, however, decreased with increasing grain number suggesting that competition for assimilates may exist at high grain number. Further evidence of the influence of assimilate supply on grain yield was obtained from several studies which showed that yield increased with leaf area duration as well as from studies where grain weight was found to decrease after reductions in assimilate supply per grain, whereas grain weight increased when assimilate supply to grain was increased. Oat crops also feature a grain abortion mechanism when assimilate supply is constrained. Yield of naked oats increased with grain number before reaching a plateau, a trend which suggests source limitation at high grain numbers. The available evidence suggests that yield is primarily determined by grain number determination but that grain yield is also potentially limited by assimilate availability in the post-anthesis period. It is recommended that crop management strategies for oats should aim both to increase grain number in the pre-anthesis period but also prolong the grain filling period after anthesis. Such a post-anthesis strategy should both reduce the possibility of yield being limited by assimilate availability and compensate for the production of smaller grains at higher grain numbers.
Soybean (Glycine max (L.) Merrill) is the most widely cultivated oilseed crop accounting for more than 50% of the world’s oilseed production. Yield gain in soybean estimated to be 0.5-0.7% per year in North America has been driven by the adoption of agronomic or management practices and genetic improvement. While genetic improvement through breeding will continue to play a significant role in enhancing yield by the development of cultivars adapted to a wide range of latitudes, biotech traits such as enhanced insect protection and weed control contribute indirectly to yield improvement. An understanding of physiological traits associated with genetic gain in yield offers vast opportunities for further advances in yield improvement. Potential targets for genetic improvement include source capacity (leaf area index, leaf area duration, carbon and nitrogen assimilation, and dry matter partitioning), sink strength (number of primary and secondary yield components, seed-filling rate and duration), and tolerance to suboptimal conditions (water limitation and high/low temperature). Manipulating single or multiple traits using breeding and biotechnology approaches will help to improve intrinsic yield potential and yield stability traits in soybean. Application of multiple technologies to improve yield gain is vital, with the changing climatic conditions and increasing global demand for food and feed.
This chapter reviews recent progress in yield potential of wheat (Triticum aestivum L.), rice (Oryza sativa L.), and maize (Zea mays L.) and examines its physiological basis. Rates of genetic gain in yield potential appear to be slowing in wheat, rice and to a lesser extent in maize, although progress has not stopped. Current genetic progress is associated with increases in both biomass and harvest index. Evidence suggests a contribution of increased radiation-use efficiency (above-ground biomass per unit radiation interception, RUE) before and around flowering is linked with recent genetic increases in biomass. Since harvest index is approaching values close to theoretical maxima in some regions and countries, future progress will increasingly depend on continued gains in biomass. In future activities to support high yield potential, priority traits include: (1) enhanced RUE before and around flowering through increased maximum photosynthetic rate at saturating irradiance at the leaf level and optimizing the coupling between the extinction of nitrogen and radiation in the profile at the canopy level; (2) deeper root systems for increased water and nutrient uptake; (3) optimized structural stem DM partitioning to increase ear/panicle DM at flowering; (4) increased fruiting efficiency (grains per unit ear/panicle dry matter at flowering) to enhance grains per unit area; and (5) increased potential grain size by reducing dry matter requirements of cell division and expansion and optimizing plant signaling. Increased understanding of these physiological processes is required to exploit traits either directly in breeding or through the development of molecular markers.
Thirty wheat genotypes from UK, CIMMYT and Pakistan were evaluated under controlled environment conditions for their potential biomass production by measuring stomatal conductance (g s ; porometry), leaf photosynthesis (IRGA), carbon isotope discrimination and carbon content (isotope ratio and mass analysis) at Rothamsted Research, Harpenden, UK during 2011. Amongst the dwarf genotypes, Rht2 and Rht3 showed lower stomatal conductance than Seri 32B, Seri 87B and Bathoor-07. For these 5 genotypes and another genotype 'Inqalab' photosynthetic performance was determined by means of IRGA measurements. Of these genotypes Inqalab had the highest photosynthetic activity (A), stomatal conductance (g s), transpiration (E) and leaf intercellular CO 2 but it also had the lowest water use efficiency (A/g s) and intrinsic water use efficiency (A/E). Seri-87B had the greatest water use efficiency (A/g s) and intrinsic water use efficiency (A/E). All the Pakistani genotypes had large stomatal conductances and high 13 C delta (Δ) and thus may be expected to produce high biomass under irrigations and optimum inputs.
Canopy architecture improvements are a major focus in modern maize (Zea mays L.) breeding because appropriate canopy architecture could allow for the adaptation to high-density planting and high utilisation efficiency of solar energy. Therefore, understanding the genetic basis of canopy architecture-related traits is important for maize breeding. In this study, an F2:3 population derived from a cross between R08 (representing a breeding pattern of lower planting density with large ears breeding pattern) × Ye478 (representing a breeding pattern of high planting density) was evaluated for nine canopy architecture-related traits in six environments, including Nanning, Ya’an, and Jinghong, in 2012 and 2013. Mixed linear model-based composite interval mapping was used to dissect the genetic basis of canopy architecture-related traits. Sixty-five quantitative trait loci (QTL) were identified for all nine traits through a joint analysis across all environments. More than 80 % of the QTL in this study did not show significant QTL × environment interactions, but epistasis played an important role in architecture-related trait inheritance. Nine chromosome segments were identified that affected multiple canopy architecture-related traits.
Economic yield of a crop is always a function of a growth rate expressed over time, but historically plant processes associated with rates probably received more attention than those associated with time. Time influences crop productivity in two ways; the time devoted to the growth of the crop can affect yield, and the time available for plant growth in any environment determines the potential resource capture by the crop. These relationships were investigated using data describing the length of the vegetative and reproductive growth phases of major grain crops. The total growth duration (TGD) of six crop species (n = 83) varied from 62 to 185 d. Vegetative growth averaged 67% of TGD while the reproductive phase accounted for 33%. Total biomass was related to the TGD, and seed yield was related to the length of the reproductive phase. There was a curvilinear relationship between TGD and reproductive phase duration with the maximum reproductive phase occurring at a TGD of similar to 110 d. Consequently, selecting a longer TGD cultivar does not necessarily increase seed yield, making it difficult to convert the extra resources available in long growing seasons into seed yield. The length of the vegetative phase can be manipulated to enhance yield or production efficiency by, for example, shortening it to place reproductive growth in a more favorable environment or to reduce the irrigation requirement. Involving time as well as rate in efforts to improve yield provides more opportunities to increase food supplies in the future.
Despite its relevance, few studies to date have analysed the role of harvest index (HI) in the responsiveness of wheat (Triticum spp.) to elevated CO2 concentration ([CO2]) under limited water availability. The goal of the present work was to characterise the role of HI in the physiological responsiveness of durum wheat (Triticum durum Desf.) exposed to elevated [CO2] and terminal (i.e. during grain filling) water stress. For this purpose, the performance of wheat plants with high versus low HI (cvv. Sula and Blanqueta, respectively) was assessed under elevated [CO2] (700 mmol mol(-1) vs 400 mmol mol(-1) CO2) and terminal water stress (imposed after ear emergence) in CO2 greenhouses. Leaf carbohydrate build-up combined with limitations in CO2 diffusion (in droughted plants) limited the responsiveness to elevated [CO2] in both cultivars. Elevated [CO2] only increased wheat yield in fully watered Sula plants, where its larger HI prevented an elevated accumulation of total nonstructural carbohydrates. It is likely that the putative shortened grain filling period in plants exposed to water stress also limited the responsiveness of plants to elevated [CO2]. In summary, our study showed that even under optimal water availability conditions, only plants with a high HI responded to elevated [CO2] with increased plant growth, and that terminal drought constrained the responsiveness of wheat plants to elevated [CO2].
Knowledge of the changes in physiological traits associated with genetic gains in yield potential is essential to improve understanding of yield-limiting factors and to inform future breeding strategies. Our objective was to identify physiological traits associated with genetic gains in grain yield of winter wheat (Triticum aestivum L.) in the UK. The growth and development of eight representative cultivars introduced from 1972 to 1995 (one tall rht-D1b cultivar and seven RHt-D1b, formerly RhT2, semidwarf cultivars) was examined in Field experiments at Sutton Boningfon in 1996-1997, 1997-1998, and 1998-1999. A linear genetic gain in grain yield of 0.12 Mg ha-1 yr-1 (1.2% yr-1) was positively correlated with both harvest index (HI) and aboveground biomass; a quadratic function fitted to the data showed that progress in HI was most apparent during the earlier phase of the 23-yr period, whereas biomass contributed most since about 1983. There was a linear increase across time of 217 grains m-2 yr-1, but no change in grain weight. Significant genetic changes across time and correlations with grain yield were also found for preanthesis radiation-use efficiency (RUE, 0.012 g MJ-1 yr-1) and water soluble carbohydrate (WSC) content of stems and leaf sheaths at anthesis (4.6 g m-2 yr-1). Our results suggest that recent genetic gains in grain yield have been based on a combination of improved growth rate in the preanthesis period, which has driven increases in number of grains per square meter, and a larger source for grain filling through increases in stem soluble carbohydrate reserves.
Germplasm from the spring wheat (Triticum aestivum L.) breeding program at the International Center for Improvement of Maize and Wheat (CIMMYT) has had a major impact on the yield of irrigated spring wheats in most developing countries in the past 30 yr. The rate and nature of yield potential progress in this germplasm was measured comparing eight outstanding short cultivars released in northwest Mexico between 1962 and 1988. They were grown under irrigation and optimal management, including disease and lodging protection, in each of six winter growing seasons (1989-1990 to 1994-1995) at the CIANO (Centro de Investigaciones Agricolas del Noroeste) experiment station in Sonora, Mexico. There were highly significant effects of cultivar on grain yield, and, although cultivar x year interaction was significant, there were few significant crossover interactions between pairs of genotypes and years in the grain yield data set. Yield averaged across the 6 yr increased linearly from 6680 kg ha-1 for the earliest cultivar, Pitic 62, to 8475 kg ha-1 for Bacanora 88, the latest. The rate of progress against year of release was 67 kg ha-1 yr-1 (r = 0.99, P < 0.001), or 0.88% per year. Grain yield progress was correlated with kernel number per square meter (r = 0.84, P < 0.01) and harvest index (r = 0.81, P < 0.02), but not with total biomass production, kernel weight, days to anthesis, spikes per square meter, or kernels per spike. Thus linear progress in yield within short germplasm has continued at least until the late 1980s, and the yield components studied did not indicate any clear direction for future progress, apart from that suggested by the strong relationships between grain yield and harvest index and grain yield and kernels per square meter, as has been seen in most studies of yield progress in cereals.
This study analyzes differences in potential yield among six semi-dwarf awned spring bread wheat (Triticum aestivum L.) cultivars recently selected in Argentina. Yield was considered as the product of number of grain per square meter (NG) and weight per grain. The NG was analyzed in terms of (i) duration of the inflorescence growth period (excluding grains), (it) crop growth rate during that period, (iii) partitioning of crop dry matter to spikes during the same period, and (iv) grain/spike weight ratio (i.e., number of grains per gram of spike). The data were obtained from two field experiments in the Province of Buenos Aires. Grain yield (range: 453-689 g m-2) was related more to NG (range: 13.3-21.3 x 103 grain m-2) than to weight per grain. Duration of spike growth period was the same (27 d) for all cultivars. During this period, intercepted photosynthetically active radiation, radiation-use efficiency (mean: 2.7 0.28 g MJ-1), and crop growth rate (mean: 26 ± 2.5 g (m-2 d-t)) were similar for all the cultivars examined. Differences among cultivars in partitioning to spikes (ranges: 28-34%) were significant. The NG, however, was not related to partitioning to the spike. There were clear differences among cultivars in the grain/spike weight ratio (range: 61-106 grain g-1); NG was more closely related to this ratio (r = 0.96, P < 0.01) than to dry weight of spikes at the end of their growth period (r = -0.30). Increments in potential yield by means of high grain/spike weight ratio were not previously reported and may be a path to future potential yield improvements.
The winter wheat (Triticum aestivum L.) cultivar Rawhide is heterogenous for the 1BL/1RS translocation. The 1BL/1RS translocation has been proven to increase grain yield and decrease end-use quality in bread wheat. The objective of this research was to investigate if the excellent yield performance of Rawhide was due to higher yielding 1BL/1RS lines compensating for lower yielding 1B lines and if the acceptable quality of Rawhide was produced by higher end-use quality 1B lines compensating for lower end-use quality 1BL/1RS lines. To do so, 19 homogeneous 1B genotypes and 18 homogeneous 1BL/1RS genotypes were selected from Rawhide. These genotypes, three composites (Composite 1B, Composite 1BL/1RS, and Composite Total), Rawhide, and three check cultivars, were evaluated in four Nebraska environments for grain yield, yield components, and end-use quality traits. No significant differences were found between chromosome classes for grain yield. The 1BL/1RS genotypes had a higher kernel weight (4%) than 1B genotypes ; however, the 1B genotypes had a greater number of spikes per square meter (5%). Composites were no different from Rawhide and from each other for grain yield and yield components. For end-use quality traits, the 1BL/1RS genotypes had a higher protein content (137 mg g -1 ), similar mixing time (4.8 min), and lower mixing tolerance (3.5) than 1B genotypes (132 mg g -1 , 5.0 min, and 4.9, respectively). However, a mixing tolerance value of 3.5 is acceptable. In general, no differences were found among the composites and between the composites and Rawhide for quality traits. Hence, the 1BL/1RS translocation was not beneficial for yield nor was it detrimental for end-use quality in this genetic background.
Preanthesis stored C and N in wheat (Triticum aestivum L.) are important in a mediterranean climate because grain filling frequently depends on the remobilization of preanthesis assimilates. We determined the effect of the rate of development of postanthesis water deficits on the remobilization of C and N to the grain using stable isotopes of C and N accumulated in the plant during the vegetative phase. Plants were grown in pots with adequate water and under similar temperature and humidity conditions until anthesis, and then were transferred to two temperature and humidity regulated greenhouses, and watering was stopped. One greenhouse was maintained at minimum relative humidity of 80% and the other at 40%. Within 6 d of anthesis the rates of development of plant water deficits became different and for the first 19 d after anthesis they were 0.10 and 0.18 MPa d(-1) for the high and low humidity regimes, respectively. Total grain C with fast development of water deficits was reduced by 24%, relative to the slow rate, because postanthesis C assimilation was reduced by 57%, while remobilization of preanthesis stored C was increased by 36%. Total grain N was not affected by the rate of development of water deficits because there was a greater retranslocation of preanthesis N with fast relative to slow development of water deficits and because there was a smaller loss of preanthesis N with fast development of water deficits. Fast development of water deficits reduced losses of preanthesis N from 25% to 6%. The absolute contributions of preanthesis C and N to the grain were 449 and 35 mg plant(-1), respectively, with fast development of water deficits. These contributions accounted for 64 and 81% of the total grain C and N, respectively. The gain in grain C-13 and N-15 in the mainstem and Tiller 1 of plants exposed to rapid development of water deficits, arose not only from remobilization from the straw of those shoots, but also seemed to be supplemented by C and N remobilized from Tillers 2 and 3.
Two trials were conducted at the Mexican National Institute of Agricultural Research (INIA) experimental station, Yaqui Valley, Sonora, Mexico, to determine the genetic yield potential of bread wheat ( Triticum aestivum L.) cultivars released in northwest Mexico over the period from 1950 to 1982, with emphasis on progress since 1970. Nonlimiting levels of fertility and moisture, a preventative pest and disease program, and netting to prevent lodging were used. Grain yield, yield components, and rates of phytomass production and grain filling were determined. Yield data on selected genotypes grown in 4 yrs of the International Spring Wheat Yield Nursery (ISWYN) at the same station were also examined. The grain yield potential of cultivars, successively released since 1950, has risen at an estimated (from a regression slope) average of 59 kg/ha/yr of release, or about 1.1%/yr. Although yield potential may have plateaued in the early 1970s, cultivars released since 1979, i.e., modern genotypes (e.g., ‘Ciano 79’, ‘Genaro 81’, ‘Glennson 81’, and ‘Seri 82’) have improved yield potential at an estimated rate similar to that prior to 1970. Improvements in grain yield were associated with increases in grain number per unit area ( r = 0.74, P < 0.01), which has risen by about 34% in modern genotypes compared to pre‐1970 cultivars, and grain number per spike ( r = 0.51, P <0.05). The 1000‐grain weight, was reduced slightly in the modern high grain number cultivars ( r = −0.76, P <0.01). Harvest indices for modern genotypes were lower than those of the landmark cultivar ‘Yecora 70’, but the modern genotypes had, on average, 16% greater phytomass than pre‐1970 cultivars. However, only 43% of the variation in grain yield was attributable to phytomass. The improvements in yield potential are mainly the result of empirical selection for grain yield. Indications were that rates of grain filling and phytomass production in modern genotypes were similar to those in Yecora 70. The higher grain yield and phytomass in modern genotypes compared to Yecora 70 was probably due to the formation and survival of a larger grain sink (more grains/m ² ) and greater C assimilation during a longer preanthesis phase.
1 vum L.) not only in high-input agricultural systems but also in low- yr1. Theses gains represent 33 to 63% of the national input systems. This study assesses the improvement in agronomic grain yield increase (Table 1). traits of winter wheat cultivars cultivated in France during the second The superiority of modern cultivars was mainly asso- half of the 20th century at four agronomic treatments: two levels of ciated with higher kernels per square meter (KN). A fungicide were combined with two levels of nitrogen fertilizer. Four- few studies have shown either an increase in 1000-kernel teen cultivars introduced between 1946 and 1992 were grown for two weight (TKW) (Cox et al., 1988) or a decrease (Sinha et years (1994 and 1995) at five locations. Selection played a major role al., 1981; Waddington et al., 1986; Perry and d'Antuono, in the increase in winter wheat yield after 1946. The contribution of 1989). The increase in KN was mostly due to an increase selection to this increase depended on the agronomic treatment and
The water-soluble carbohydrate (WSC) that accumulates in the stems of wheat during growth can be an important contributor to grain filling, particularly under conditions when assimilation is limited, such as during end-of-season drought. WSC concentration was measured at anthesis across a diverse set of wheat genotypes over multiple environments. Environmental differences in WSC concentration were large (means for the set ranging between 108 and 203 mg g(-1) dry weight), and there were significant and repeatable differences in WSC accumulation among genotypes (means ranging from 112 to 213 mg g(-1) dry weight averaged across environments), associated with large broad-sense heritability (H= 0.90 +/- 0.12). These results suggest that breeding for high WSC should be possible in wheat. The composition of the WSC, examined in selected genotypes, indicated that the variation in total WSC was attributed mainly to variation in the fructan component, with the other major soluble carbohydrates, sucrose and hexose, varying less. The degree of polymerisation (DP) of fructo-oligosaccharides was up to similar to 13 in samples where higher levels of WSC were accumulated, owing either to genotype or environment, but the higher DP components (DP > 6) were decreased in samples of lower total WSC. The results are consistent with fructan biosynthesis occurring via a sequential mechanism that is dependent on the availability of sucrose, and differences in WSC contents of genotypes are unlikely to be due to major mechanistic differences.
Cultivar comparisons have suggested that the 1BL/1RS wheat (Triti-cum aestivum L.)-rye (Secale cereale L.) chromosomal translocation enhances agronomic performance and environmental stability of wheat. This advantage has been attributed either to disease resistance genes or to unproved adaptation genes on the 1RS segment. The objective of this study was to determine the effect of 1BL/1RS without the confounding effect of cult!var background by evaluating 17 homoge-neous IB, 20 heterogeneous 1B:1BL/1RS, and 22 homogeneous 1BL/ 1RS lines. The lines were randomly selected from the cross 'SiouxlandV 'Ram'. The 59 progeny lines and the two parents were tested in seven Nebraska field environments with a randomized complete-block design. Data were obtained for grain yield, components of yield, grain volume weight, anthesis date, plant height, and leaf rust infection. The 1BL/ 1RS class was 9% higher yielding than IB and heterogeneous classes. This yield advantage was attributed to increased kernel weight, which was generally expressed in lower yielding environments. Differential response to disease pressure did not explain yield differences. Within chromosome classes, differences in grain yield were attributed more to variation in number of spikes per square meter not kernel weight. The grain yield advantage of the 1BL/1RS appeared to be associated with a postanthesis stress tolerance, which resulted in increased kernel weight of the 1BL/1RS genotypes.
Field experiments were conducted in the eastern wheat belt of Western Australia in a dry year with and without irrigation (1987) and in a wet year (1988), comparing three cultivars of wheat differing in height and yield potential. The aim of the study was to determine the contribution of remobilisable stem dry matter to grain dry matter under different water regimes in old and modern wheats.
Stem non-structural carbohydrate was labelled with C-14 1 day after anthesis and the activity and weight of this pool and the grain was measured at 2, 18 and 58 days after anthesis. Gutha and Kulin, modern tall and semi-dwarf cultivars respectively, yielded higher than Gamenya, a tall older cultivar in all conditions, but the percentage reduction in yield under water stress was greater for the modern cultivars (41, 34 and 23%). In the grain of Gamenya, the increase in C-14 activity after the initial labelling was highest under water stress. Generally, loss of C-14 activity from the non-structural stem dry matter was less than the increase in grain activity under water stress but similar to or greater than grain activity increase under well watered conditions. Averaged over environments and cultivars, non-structural dry matter stored in the stem contributed at least 20% of the grain dry matter.
A field experiment was conducted at Merredin in the eastern wheat belt of Western Australia, comparing 10 wheat cultivars representing old and modern wheats. The aim of the study was to identify any morphological and physiological characters associated with higher grain yield of modern wheat cultivars.The modern cultivars reached double ridge, terminal spikelet, anthesis and maturity earlier than the old cultivars, but modern cultivars had a longer duration between double ridge and terminal spikelet stage. The number of leaves on the main stem generally decreased from old, Purple Straw (14) to modern cultivars like Kulin (8). The modern cultivars had a shorter phyllochron interval than the old cultivars. The old cultivars also produced more tillers per plant (7.3) and had a lower percentage (35%) of ear bearing tillers, as compared with 3.9 and 51% for modern cultivars.The green area index and ground cover was higher in old than modern cultivars. However, the efficiency of conversion of photosynthetically active radiation to dry matter was slightly greater for modern cultivars. Although dry matter at final harvest was similar between cultivars, there was a trend for higher dry matter production with modern cultivars. The post-anthesis green area duration was longer with modern cultivars and grain yield increased with increase in post-anthesis green area duration.Grain yield and HI increased consistently from old to modern cultivars. The most recent cultivar Kulin had the highest yield and second highest harvest index, which were 63% and 48% respectively higher than the oldest cultivar, Purple Straw. Increases in grain yield in the modern cultivars were associated with increased grains spikelet-1 and grains ear-1. Mean grain weight showed a slight reduction with modern cultivars. The results are discussed in relation to future improvement in yield.
Experiments in three dry years, 1993/94, 1994/95 and 1995/96, on a medium sand at ADAS Gleadthorpe, England, tested responses of six winter wheat cultivars to irrigation of dry-matter growth, partitioning of dry matter to leaf, stem and ear throughout the season, and to grain at final harvest. Cultivars (Haven, Maris Huntsman, Mercia, Rialto, Riband and Soissons) were selected for contrasts in flowering date and stem soluble carbohydrate. Maximum soil moisture deficit (SMD) exceeded 140 mm in all years, with large deficits (>75 mm) from early June in 1994 and from May in 1995 and 1996. The main effects of drought on partitioning of biomass were for a decrease in the proportion of the crop as lamina in the pre-flowering period, and then earlier retranslocation of stem reserves to grains during the first half of grain filling. Restricted water availability decreased grain yield by 1·83 t/ha in 1994 (P<0·05), and with more prolonged droughts, by 3·06 t/ha in 1995 (P<0·001) and by 4·55 t/ha in 1996 (P<0·001). Averaged over the three years, grain yield responses of the six cultivars differed significantly (P<0·05). Rialto and Mercia lost only 2·8 t/ha compared with Riband and Haven which lost 3·5 t/ha. Losses for Soissons and Maris Huntsman were intermediate. In the two years with prolonged drought, the biomass depression was on average greater for Haven (6·0 t/ha) than for Maris Huntsman (4·2 t/ha) (P<0·05). Thus, the grain yield sensitivity of Haven to drought derived, in part, from a sensitivity of biomass growth to drought. Harvest index (HI; ratio of grain to above-ground dry matter at harvest) responses of the six cultivars to irrigation also differed (P<0·05) and contributed to the yield responses. The smallest decrease in HI of the six cultivars with restricted water availability was shown by Rialto (−0·033); this partially explained the drought resistance for this cultivar. The largest decrease was for Maris Huntsman (−0·072). The cultivars differed in flowering dates by up to 9 days but these were poorly correlated with grain yield responses to irrigation. Stem soluble carbohydrate at flowering varied amongst cultivars from 220 to 300 g/m2 in the unirrigated crop; greater accumulation appeared to be associated with better maintenance of HI under drought. It is concluded that high stem-soluble carbohydrate reserves could be used to improve drought resistance in the UK's temperate climate, but that early flowering seems less likely to be useful.
Two field experiments were carried out with seven wheat cultivars (three of them, including a commercial hybrid, released during the last 10 years) representing different eras of plant breeding, to evaluate genetic improvement over the last century in grain yield, height, biomass, harvest index and grain yield components. Plots were fertilized and irrigated, and lodging and diseases were prevented.
Main culm height was negatively correlated with the year of release of the cultivars, probably as a consequence of selection for increased lodging resistance. There was no significant association between total above‐ground biomass and year of release of the cultivars. On the other hand, grain yield increased as newer cultivars were released. Results indicate that during recent years harvest index has been kept as the main attribute responsible for increases in grain yield. In general, number of grains/m ² was associated with increases in grain yield during the century. However, the newest cultivars showed an increased grain weight. In both growing seasons, cultivars released before 1980 showed a trend towards reduced grain weight, but cultivars released after 1987 had a similar number of grains per m ² with a higher grain weight than their predecessors. This was probably because the most modern cultivars have a longer grain‐filling duration with a similar length of growth cycle.
The physiological and genetic basis of yield improvement in wheat isonly partially understood. Nonetheless, a significant increase in yield andbiomass has been observed in several backgrounds when alien chromatinassociated with Lr19 was introgressed from Agropyronelongatum. Theoretically, higher yield and biomass may be achievedthrough (i) greater interception of incident radiation, (ii) increasedradiation use efficiency, (iii) a more optimal source-sink balance permittinghigher sink demand and/or a higher partitioning of assimilates to yield. Theobjectives of the current study were to evaluate the performance of nearisogenic lines differing in Lr19 to observe the physiological basis ofsuperior performance. Lr19 was associated with increases in yield(average 13%), final biomass (10%) and grain number (15%) in allbackgrounds studied. Differences were not associated with improved lightinterception based on measurements of biomass shortly after canopyclosure, nor with improved radiation use efficiency (RUE) prior to grainfilling based on biomass accumulation rate and direct measurement offlag-leaf photosynthetic rate prior to anthesis. Lr19 was associatedwith an increased partitioning of biomass to spike growth at anthesis(13%), a higher grain number per spike, and higher RUE and flag-leafphotosynthetic rate during grain filling. The mechanism causing increasedpartitioning of assimilates to spikes relative to the rest of the plant in Lr19 isolines was apparently not related to phenology or assimilationcapacity.
The most appropriate measure of yield has changed in the past, and may well continue to do so as agriculture itself evolves. The earlier criterion of number of grains harvested per grain sown has been largely displaced by yield per hectare per crop, which is the basis of the following discussion. But in multiple cropping sys-tems, especially in the tropics, yield per hectare per day is becoming ever more important, while yields per unit of applied energy or water or phosphorus or labor are also important considerations.
In a field study with six winter wheat genotypes losses of dry matter from the stems between 30 June and maturity averaged 172 g m⁻² (range 82–236), there being significant differences in loss between genotypes. Respiration from the stems during the same period was estimated to amount to 106 g m⁻² (range 104–225). The amount of dry matter mobilized from the stems, calculated by difference, was estimated as 66 g m⁻². The loss of ethanol- and water-soluble carbohydrate from the stems (170 g m⁻²; range 124–215) was very similar to the dry weight loss.
Carbon-14 labelling was used to trace the time course and the amount of the movement of assimilates from the vegetative organs to the grain. Only 14⋅3 per cent (range 10⋅3–21⋅0) of the products of photosynthesis over the period 21 May-20 June were relocated to the grains. This relocation amounted to an average of 7 per cent (range 5⋅7–11⋅4) of the final grain weight. It was estimated that during the 18 days following anthesis on 20 June photosynthesis contributed 48 per cent (range 39–55) of the final grain dry weight. Of this, about half was translocated to the grain within 10 days of initial assimilation. The remainder appeared to be stored temporarily in the stems and leaves and translocated to the grains during the period 17–29 July. In general, relocation of dry matter from the vegetative organs to the grains, assessed by carbon-14 labelling, was greatest in those genotypes (Hobbit and Sportsman) which lost most dry weight from the stems and leaves.
Experiments in three dry seasons (1993/94, 1994/95, 1995/96) on a loamy medium sand at ADAS Gleadthorpe, Nottinghamshire, England tested responses of green area, radiation interception, water uptake and above-ground dry matter growth of six wheat cultivars to irrigation. Cultivars differing in date of introduction (Haven 1987, Maris Huntsman 1969, Mercia 1983, Rialto 1991, Riband 1985 and Soissons 1989) were chosen for contrast in flowering time and maximum green area. Maximum soil moisture deficit (SMD) exceeded 140 mm in all years, with large deficits (> 75 mm) from early June in 1994 and more prolonged large deficits in 1995 and 1996. Restricted water availability first affected canopy expansion at a SMD of 74 mm (50% available water capacity; AW), and canopy senescence at 95 mm (64% AW). Decreases in biomass at harvest were larger with prolonged droughts in 1995 and 1996 (4245·7 g/m2/mm. The susceptibility of Haven to drought was possibly due to restricted water uptake, depression of radiation use efficiency (RUE) and accelerated senescence. The cultivars differed in flowering by up to 9 days but date of flowering correlated poorly with biomass response to irrigation. Early flowering was, however, correlated with favourable distribution of seasonal water use with respect to the grain filling period. The maximum green area index (GAI) of cultivars varied from 4·4 to 5·3 (P < 0·01), but differences were countered by shifts in the extinction coefficient (K), such that season-long radiation interception varied little. Green area index maxima did not therefore relate to the pattern of growth or water use, and they were correlated poorly with the biomass responses. Cultivars did not differ in their maximum depth of water extraction; they all extracted water to 1·65 m depth in each year. It is concluded that early flowering and high WUE might offer scope for improving drought resistance in the UK's temperate climate, but that small maximum GAI seems less useful.
Two trials were conducted to determine the effect of IB/1R chromosome translocation on selected agronomic characteristics of spring bread wheats(Triticum aestivum L.)developed at the International Maize and Wheat Improvement Center(CIMMYT). Five bread wheat genotypes with a chromosome IB/1R translocation and five without representing a sample of high yielding germplasm were identified for the experiment. NonIimiting levels of fertility and moisture with a preventive pest and disease program were used. Plant height, days to heading, grain yield, aboveground biomass at maturity, harvest index, yield components and test weights were determined. Genotypes with the IB/1R chromosome translocation had 2.2% higher aboveground biomass yield, 2.1 Vo more spikes m2, 1.12 g higher 1, 000-grain weight and 0.8 kg/ha1 higher test weight. The non-1B/1R genotypes had 0.8% higher harvest index and 0.6 cm longer spikes. Cultivar comparisons indicated that the IB/1R group headed 2.5 days later than the IB group.
The agronomical, physiological and qualitative characteristics of 34 representative cultivars of bread wheat belonging to 7 generations (groups) of cultivars produced by Italian breeders over 90 years have been evaluated.
The effects of Rht1 and Rht2 alleles on the dynamics of floret development in isogenic lines (dwarf, DD; semi-dwarf, SD and standard height, SH) of spring wheat were investigated. Studies were conducted on wheat grown in the field in each of 4 years and where water and nutrients were non-limiting. The number of grains per spike was significantly greater in the lines with Rht alleles than in the SH lines. Grain number for each line was such that DD>SD>SH. Grains per spike varied with the number of grains per spikelet rather than number of spikelets per spike. Grains per spikelet in turn varied with the number of fertile florets at anthesis. Florets were considered fertile when male and female reproductive organs had developed green anthers and bifidum stigma, respectively. The dwarfing genes had no effect on the percentage of fertile florets setting grain. Increased number of fertile florets per spikelet due to the presence of Rht1 and Rht2 alleles in the genome was a consequence of the higher number of relatively distal primordia, to progress to the stage of fertile floret at anthesis in the DD and SD than in the SH lines. This ability to allow that a greater proportion of distal florets maintain a normal rate of development was related to the fact that Rht alleles produced a more favourable assimilate partitioning to the spike during the pre-anthesis period associated with the reduction in stem growth imposed by Rht alleles. This allowed a higher proportion of the later-initiated floret primordia to produce fertile florets at anthesis.
A field experiment was undertaken with a set of near-isogenic spring wheat lines (cv. Triple Dirk) to determine the influence of the Rht1 and Rht2 alleles on the deposition of carbon in the stem, and the subsequent use of these reserves during grain growth. The amount of dry matter stored and mobilized was estimated by the measurement of changes in masses of stem from frequent harvests. Deposition or absolute reserve was defined as the sum of the increments in mass in each segment of the large culm between the time that the segment ceased extending and the time that it reached maximum mass. The incorporation of the Rht1 and Rht2 alleles into a Triple Dirk background reduced the absolute amount of stored carbon in the stem by 35 and 39%, respectively. This was a consequence of the 21% reduction of stem height in Rht1 and Rht2 lines. Use or mobilization of reserve was defined as the sum of the decrements in mass in each segment of the large culm between maximum and maturity. The alleles did not confer an ability to mobilize more of the stored stem reserves in absolute terms, although the efficiency of use of stem reserves (i.e. use as a proportion of deposition) was higher in Rht1 than in rht or Rht2 . The possible contribution of stored carbon in the stem to final grain yield was estimated to be 22, 18 and 14% in the rht, Rht1 and Rht2 lines. In these estimates, the loss of mass was adjusted by 33% to allow for respiration. It was concluded that the larger stem reserves in rht wheats are of no real advantage under favourable environmental conditions, and may in fact be a disadvantage if the accumulation of that extra dry matter results in a reduction of sink size.
The wheat (Triticum aestivum L.)-rye (Secale cereale L.) translocation, 1BL.1RS, has been reported to enhance yield potential in hard wheat germplasms. This study was designed to evaluate the impact of 1BL.1RS on yield potential in soft red winter wheat. Agronomic traits associated with yield potential were measured in 40 F9-derived sister lines in two soft red winter wheat genetic backgrounds, SW85*294 and SW85*5626. The presence of 1BL.1RS had no significant impact on grain yield, kernel weight, biological (total aboveground) yield, harvest index, fertile tillers, spikelets per head, or kernels per spikelet. This effect was independent of production environment in which the translocation was assessed. The presence of the translocation caused a 3.3- and 4.0-cm reduction in plant height in SW85*5626 and SW85*294, respectively. A significant reduction in lodging was associated with reduced height. Heading date was delayed ≃1 d in SW85*294 but was not affected in SW85*5626. The effect of genetic background was large relative to the effect of the translocation for all traits measured. These data suggest that where grain yield is a primary objective of the breeding program, emphasis should be placed on selection for genes on other wheat chromosomes rather than for the presence of the 1BL.1RS translocation.
The purpose of this study was to examine how differences in leaf angle may affect grain yield of wheat by changes in the relative contribution of yield components or changes in the pattern of crop growth. Leaf structural changes and their influence on plant water status and carbon isotope discrimination were also studied. A collection of pairs of bread wheat (Triticum aestivum L.) lines (PL) differing in leaf angle were grown under irrigation during two consecutive years at Sonora, Mexico. Erect leaf lines did not have higher yields than droopy leaf lines, but erect lines did have 5 to 16% greater number of kernels per unit of ground area. Droopy lines had a lower number of spikes per unit ground area, a greater number of kernels per spike, and a greater weigh of mature kernels than droopy lines. Therefore, the lack of differences in yield apparently was associated with yield component compensation. Differences between PL in discrimination against C-13 (Delta) in mature kernels, relative water content of flag leaves, canopy temperature, leaf area, and degree of leaf tip burning suggested higher transpiration rates (and thus lower water use efficiency) in the erect lines. For example, Delta in kernels was consistently higher in the erect lines than in the droopy lines. In addition there was a significant (r = - 0.85, P < 0.05) negative correlation between canopy temperature during grain filling and Delta. Grain yield was positively correlated (r = 0.50, P < 0.05) with h of kernels. Although wheat genotypes with erect leaves did not show conclusive superiority, nevertheless selection for a more erect growth habit may result in increased yield. However, the possible existence of allometric relationships among leaf erectness and smaller leaves, spikes, and stems make progress in increasing yield a complex task.
In hexaploid wheat (Triticum aestivum L.) disease resistance genes transferred from alien sources are often associated with undesirable traits. Replicated trials using near-isogenic lines of spring wheat 'Seri 82' were conducted for 2 yr under non-moisture stress and simulated moisture stress conditions to determine the effects of the 7DL.7Ag and 1BL.1RS translocations [from Agropyron elongatum (Host) Beauv. and Secale cereale L., respectively] on grain yield and related traits. Mean grain yield of the lB lines was significantly higher (3.2%) than that of the 1BL-1RS translocation lines in non-moisture stress trials, but not significantly higher in the moisture stress trials. The mean grain yields of the five highest yielding reconstituted Seri 82 genotypes (1BL.1RS) were significantly lower than that of the genotypes without the 1BL.1RS translocation in non-moisture stress (3.2%) and moisture stress (5.2%) conditions. Incorporation of the 7DL.7Ag translocation caused a significant increase (9%) in biomass at harvest in non-moisture stress trials. The mean grain yields of the five highest yielding 7DL.7Ag lines were significantly higher (8.2%) than the reconstituted Seri 82 genotypes in non-moisture stress conditions and more than 16% lower under moisture stress. Lower grain yields of the 7DL.7Ag fines under moisture stress could be due to their excessive pre-heading biomass production. Several yield-related traits of the near-isogenic genotypes varied significantly. Presence of each translocation caused lateness and, when present together, the 1BL.1RS and 7DL.7Ag translocations delayed heading and maturity by 7 and 5 d, respectively. The genetic background of the recipient wheat can affect the utility of a translocation.
Photoperiod sensitivity is an important feature of flowering time regulation, which enables wheat plants to adapt to a wide range of environments. Although some work has been done on how time to heading or flowering respond to photoperiod in relation to particular Ppd alleles, there is little evidence on whether these alleles contribute to responses at different phases and to associated yield component generation. The aims of this paper were: (i) to analyse the effects of photoperiod on substitution lines with contrasting Ppd alleles, in terms of duration of particular phases, (ii) to determine if there is any relationship between these alleles and the parameters of photoperiod response (photoperiod sensitivity, optimum photoperiod and basic length of the phase), and (iii) to analyse the effects of different photoperiods applied before and after the onset of terminal spikelet on yield component generation. The effects of length and timing of photoperiod extensions on these traits were analysed under field conditions in Chinese Spring and two substitution lines differing in photoperiod sensitivity.
Translocations of the short arm of rye (Secale cereale L.) chromosome 1R in wheat (Triticum aestivum L. em Thell.) offer several resistance genes, and possibly increase yield, but adversely affect bread-making quality. The objective of this study was to determine the frequency of such translocations in wheats bred in the USA. Two hundred and seven entries in six major 1989 wheat nurseries and 30 entries in the 21st International Winter Wheat Performance Nursery were cytologically screened using C-banding (...)
The 1RS.1BL translocation is widely used by wheat (Triticum aestivum L.) breeders to enhance agronomic peformance and particularly grain yield. Research is lacking that compares agronomic trait expression in closely related stocks with or without the translocated chromosome arm. Our objective was to determine the effects of 1RS.1BL on means and genetic variances for grain yield and other agronomic traits in two hard red winter wheat populations segregating for the «Aurora» translocation. Two field experiments were conducted using different genetic materials derived from two crosses, OK83398 × «Chisholm» and OK83398 × «Arkan». In Experiment 1, 25 pairs of F 5 -derived near-isolines homozygous for either 1B or 1RS.1BL were evaluated in three environments [...]
in the soil-drying treatments than in the well-watered ones, indicating that soil drying enhanced senescence. Nonstructural carbohydrate in delayed, such wind may dehydrate the wheat rapidly the stem and sheath at maturity was greatly reduced, and the parti- and lead to reduced grain weight. If an applied soil tioning of fixed C from flag leaves into the grains and the final harvest drying accelerates senescence so that the wheat matures index were significantly increased by soil drying under both nitrogen before the adverse weather occurs, grain filling and treatments for the three cultivars. Soil drying shortened the grain- hence yield might be improved. filling period but grain-filling rate was substantially increased by all the soil drying treatments except one NN treatment with severe soil MATERIALS AND METHODS drying in the pot experiment. Soil drying actually increased the grain yield at HN in both experiments. We conclude that senescence induced Pot Experiment
Knowledge of changes associated with advances in crop productivity is essential for understanding yield-limiting factors and developing strategies for future improvement. Our objective was to identify plant traits associated with gains in grain yield of winter wheat (Triticum aestivum L.) in the Great Plains. Twelve landmark cultivars and one experimental line were compared with 'Turkey' (introduced 1873) at Hutchinson (Clark-Ost complex soil) and Manhattan (Reading silt loam soil), KS, during 1996-1997 and 1998-1999. Agronomic traits, leaf rust infection (caused by Puccinia recondita Rob. ex Desm. f. sp. tritici), and grain yield and its components were measured. Grain yields ranged from 2718 kg ha -1 for Turkey to 4987 kg ha -1 for the experimental line, with mean genetic gains of 0.16% per year for early genotypes and 0.63% per year for recent genotypes. Kernel number per unit of soil area had the highest phenotypic correlation with grain yield and contributed most to its genetic gain. Gains in spike numbers per unit of soil area and above-ground biomass also contributed significantly to higher yields of some genotypes. Significant genetic changes over time and correlations with grain yield were observed for early heading, decreased height, and reduced lodging and leaf rust but not for kernel weight. Our results suggested that yield components that form during vegetative phases (spike numbers per unit of soil area and kernels per spike) when conditions for growth are generally favorable are more amenable to genetic improvement than kernel weight, which forms during maturation when moisture and temperature are often unfavorable.
RESERVES of assimilate present in wheat and barley crops at flowering, and available for later translocation to the grains, could buffer grain yield against environmental stresses during grain filling. This so-called pre-anthesis assimilate contribution to grain yield can be expressed as a percentage of yield (P
1). Archbold1, and later Thorne2, concluded that P
1 was small, being no more than 20%2. But only one result (12% for irrigated wheat at Cambridge3) refers to a crop in the field as distinct from plants in pots, and no studies considered the effect of stress during grain filling. Recently Gallagher et al.
4,5 reported substantial contributions: P
1 averaged 43% over six crops of wheat and barley at Nottingham; this amounted to more than 300 g per m2 of dry material in two crops and, in the severe drought of 1970, 39% of total dry matter present at anthesis. They assumed, with some supporting evidence from one barley crop6, that the pre-anthesis contribution was given by the decrease from anthesis to maturity in dry weight of non-grain parts of the crop. In situ labelling with 14CO2 of the whole crop canopy at frequent intervals before and after anthesis would seem to be the least equivocal way of estimating P
1. Using this method we have determined P
1 in wheat and barley. It averaged only 12% (watered crops) and 22% (droughted crops), and did not agree with estimates for the same crops obtained by the method of Gallagher et al.
4,5.
Selections for erect-(E) and lax-leaf (L) posture in winter wheat were made from a cross between parents which contrasted in the character. By the F 5 generation there were consistent, heritable differences between E and L lines. The lines were evaluated in three field experiments and a glasshouse experiment.
In an experiment in which plots were automatically sheltered from rain and in which there were three irrigation treatments, there was no treatment-posture interaction, and over all treatments E lines outyielded L lines by 0·26 t/ha. When fully irrigated the water use of both E and L lines between 1 May and maturity was approximately 280 mm. Withholding water caused a reduction in water use and a corresponding reduction in grain yield for both E and L lines.
When the four most erect- and the four most lax-leaved lines were considered over all three field experiments, E lines maintained a slight, though not significant, grain yield advantage of 0·17 t/ha over L lines. However, the E lines produced significantly more biomass, averaging 0·7 t/ha more than L lines, and this extra biomass was not produced at the expense of additional water requirement. However, results from the glasshouse experiment suggested that the E lines may be more susceptible to a substantial pre-anthesis drought.
It is concluded that varieties of winter wheat with the erect-leaf habit may provide an opportunity of increasing biomass production. In an environment in which a preanthesis drought is unlikely to occur, such varieties may give the highest yields. However, on light soils prone to early drought or at sites which would not permit the maximum expression of leaf area index at anthesis, varieties with a lax-leaf posture may give greater yield.
Field experiments comparing 13 winter wheat varieties representing very old, old, intermediate and modern groups were carried out over three seasons. The experimental sites were on soils of high fertility and weeds, diseases and pests were controlled by applications of proprietary agrochemicals. Lodging was prevented by supporting the plants with coarse-mesh netting.
The average yield of all varieties over the three harvest years 1984, 1985 and 1986 was 7·7 t/ha (at 15% moisture content). Compared with the very old varieties which were grown by farmers during the 19th century, the modern varieties gave 59% more grain, had 14% more ears/m ² and 30% more grains per ear, but a similar mean grain mass. The modern varieties yielded slightly more biomass (total above-ground dry matter at harvest), were much shorter and reached anthesis about 6 days earlier than the older ones. In 1984, when the yields were greater than in 1985 and 1986, the yield advantage of the modern varieties was more in percentage and absolute terms than in the other years. Also, in 1984, the differences between the very old and the modern varieties in biomass was the greatest.
The genetic gain in yield measured in these experiments is compared with those estimated for other countries and reasons for the variation are discussed.
Comparisons involving 28 random F2-derived F6 wheat (Triticum aestivum L.) lines from the cross, ‘Nacozari’/‘Seri 82’, suggested that advanced derivatives with the 1BL/1RS chromosome translocation possess superior agronomic performance in both full and reduced irrigation conditions when compared with 1B derivatives. This performance advantage was attributed to high grain yield, above-ground biomass at maturity, grains/spike, 1000-grain weight and test weight. The 1BL/1RS lines were shorter with delayed flowering and maturity. The superiority of the 1BL/1RS translocation group on grains/m2 was expressed only under the full irrigation environment. Higher harvest index, longer spike-length and grain-filling period were detected only under reduced irrigation conditions. A significant grain yield relationship with test weight was detected only among the 1BL/1RS genotypes, indicating that they possess heavier and plumper grains than the 1B genotypes.
Yield potential can be expressed as a product of light interception, radiation use efficiency (RUE), and the partitioning of biomass to grain yield, or harvest index (HI). Traits related to early or late light interception have not been shown to be associated with genetic improvement of spring wheat yield in favourable environments. It is, however, well established that yield improvement is largely a result of increased HI, although the most recent studies comparing genetic progress in HI over time in spring wheat indicate that it has not made any additional progress since the mid 1980s. These observations suggest that future genetic progress in yield will most likely be achieved by focusing on constraints to RUE. Considering the possibility that RUE may be influenced indirectly by sink limitation, it is apparent that biomass may be increased by increasing grain number, for example. Experiments with high yielding spring wheat lines containing the alien translocation 7DL.7Ag showed increased grains m-2 (15%), yield (12%), and biomass (9%) compared with controls. The translocation was also associated with a larger investment in spike mass at anthesis (15%), more grains/spike (10%), and increased flag-leaf photosynthetic rate during grain-filling (20%). The data suggest that increased biomass in 7DL.7Ag lines was due to significantly increased RUE post-anthesis, as a result of a larger kernel number (sink) that increased the demand for photosynthesis during grain-filling. The hypothesis that increased photosynthesis and RUE may respond directly to a larger number of grains/spike was tested experimentally by imposing a light treatment during boot stage. The treatment was associated with a small increase (5%) in the proportion of biomass invested in spike mass at anthesis, reflected by on average three extra grains/spike at maturity. The treatment was associated with 25% more yield and 22% more biomass than controls, while carbon assimilation rate measured on flag-leaves during grainfilling was 10% higher than controls. The results suggest that RUE can be increased indirectly by increasing sink strength and that the current yield limiting process in spring wheat is the determination of kernel number. Experimental data are presented on how spike fertility may be increased through breeding, for example by introgression of the multi-ovary trait to increase grain number per spikelet. In addition, results of analysis of the physiological bases of genotype × year interaction in high yield environments are presented in the context of how such information can provide a focus for genetic studies of sink limitation.
Two types of source contribute photosynthate for grain filling in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.), current photosynthate transferred directly to the grain and photosynthate redistributed from reserve pools in vegetative tissues. Reserve pools provide the substrate needed to maintain transport and the supply of assimilate to grains during the dark period of the diurnal cycle and during the latter part of grain filling, when the photosynthetic apparatus is senescing and the rate of dry matter accumulation of grains exceeds the rate of dry matter accumulation of the total crop. In addition reserve pools provide a means by which the current rates of photosynthate production and of photosynthate use in grain filling are allowed to proceed (at least in part) independently from each other. There is evidence that all photosynthetic organs (leaves, glumes and exposed portion of the peduncle) contain one or more diurnal carbohydrate storage pools. Diurnal storage of sucrose seems to be much more important than the transient storage of starch. There is little evidence for fructan pools serving a role as a net source of carbon during the dark period of the diurnal cycle. However, fructan is the most important longer-term reserve carbohydrate of vegetative tissues. Fructan accumulation occurs mainly in the extended internodes and leaf sheaths and usually terminates within three weeks following anthesis, after which fructan is gradually lost until grain maturity. The accumulation and loss of fructan are greatly influenced by environmental conditions and treatments that alter the longer-term balance between photosynthate production by the plant and photosynthate use in grain filling. Observations are consistent with the view that fructan accumulation in expanded vegetative tissue is not competitive with grain filling, but the fructan pools accept surplus photosynthate during periods of low demand by grains and provide photosynthate during longer-term deficits in current photosynthate production. Even under optimal conditions for photosynthesis it is likely that half or more of the photosynthate in mature grains is temporarily deposited in one or more reserve pools before being transferred to the grain. Neither the efficiency of reserve utilization in grain filling nor its potential variability in different genotypes and environments are known. Also, very little is known about the mechanisms that control the partitioning of photosynthate between the grain and reserve pools and the allocation to different types of reserve pools. Future progress in the understanding of photosynthesis-yield relationships will likely depend to a great extent on improved knowledge of the controls that govern photosynthate deposition and redistribution in the different pools of reserve carbohydrate.
Breeding for improved productivity has been tremendously successful in the last half-century, but needs to be even more efficient in the future. Hope based on contributions from molecular biology for improved yield potential seems to depend upon an improved knowledge of yield physiology. This knowledge may assist breeding either directly, recommending selection criteria, or indirectly identifying simpler traits that could be reliably mapped and selected for through marker-assisted selection. Physiological traits associated with improved performance under water-limited conditions, include phenology (that allows the crop to escape stresses) and those associated with improved water use, water use efficiency and partitioning. Undoubtedly, earliness has been the predominant trait improved for under Mediterranean conditions, and may not be a prospective trait for future breeding. Different traits that may confer the ability to the crop for capturing more water, such as deeper root systems or osmotic adjustment, may be unworkable in terms of their direct use in selection and surrogates would be needed. For instance, canopy temperature depression and discrimination against 13 C may be used to assess improved ability to capture water (in these cases yield is positively related to discrimination against 13 C in grains). Early vigour, which allows faster ground coverage, also increases the amount of water actually transpired by the canopy by reducing direct evaporation and presents substantial intra-specific variation, and selection for this trait may be successfully carried out either directly or through the use of vegetation indexes. Improved water use efficiency based on transpiration efficiency is largely restricted to conditions where additional water is not available. A constitutively low stomatal conductance or a high stomatal sensitivity may optimise the transpiration efficiency. In this context, discrimination against 13 C is also a simple and reliable measure of water use efficiency, and in cases in which no major differences in capturing water is possible discrimination against 13 C correlates negatively with yield. Substantial further improvements in partitioning may be limited in most cereals.
δ, C isotope composition relative to Pee Dee Belemnite
WSC, water-soluble carbohydrates
N, nitrogen
C, carbon
cv, cultivar
ME, efficiency of mobilized pre-anthesis C utilization in grain filling (g C g–1C)
Significant mobilization of protein and carbohydrates in vegetative plant parts of wheat regularly occurs during grain filling. While this suggests a contribution of reserves to grain filling, the actual efficiency of mobilized assimilate conversion into grain mass (ME) is unknown. In the present study the contribution of pre-anthesis C (C fixed prior to anthesis) to grain filling in main stem ears of two spring wheat (Triticum aestivum L.) cultivars was determined by ¹³C/¹²C steady-state labelling. Mobilization of pre-anthesis C in vegetative plant parts between anthesis and maturity, and the contributions of water-soluble carbohydrates (WSC) and protein to pre-anthesis C mobilization were also assessed. Experiments were performed with two levels of N fertilizer supply in each of 2 years. Pre-anthesis reserves contributed 11–29% to the total mass of C in grains at maturity. Pre-anthesis C accumulation in grains was dependent on both the mass of pre-anthesis C mobilized in above-ground vegetative plant parts (r² = 0·87) and ME (defined as g pre-anthesis C deposited in grains per g pre-anthesis C mobilized in above-ground vegetative plant parts; r² = 0·40). ME varied between 0·48 and 0·75. The effects of years, N fertilizer treatments and cultivars on ME were all related to differences in the fractional contribution of WSC to pre-anthesis C mobilization. Multiple regression analysis indicated that C from mobilized pre-anthesis WSC may be used more efficiently in grain filling than C present in proteins at anthesis and mobilized during grain filling. Possible causes for variability of ME are discussed.
The T1BL.1RS wheat (Triticum aestivum L.) - rye (Secale cereale L.) translocations have been of particular interest and are
widely used in bread wheat breeding programs. The objective of this study was to determine the effect of the T1BL.1RS chromosome
on grain yield and its components using 20 near-isolines of spring bread wheat cultivar ‘Seri M82’ (10 homozygous for chromosome
1B substitution and 10 homozygous for T1BL.1RS). The test lines have been produced by substituting the 1B chromosome in Seri
M82 (T1BL.1RS, T1BL.1RS) through backrossing. Two field experiments were evaluated under optimum (five irrigations) and reduced
(one irrigation) moisture conditions for two consecutive production cycles at the Mexican National Agricultural Research Institute,
Ciudad Obregon, Sonora, Mexico. The presence of T1BL.1RS had a significant effect on grain yield, harvest index, grains/m2, grains/spike, 1000-grain weight, test weight, flowering date and physiological maturity in both moisture conditions. The
agronomic advantage of the 1B substitution lines on above-ground biomass yield at maturity, spikes/m2and grain-filling duration was expressed only under the optimum moisture condition. The presence of T1BL.1RS increased grain
yield 1.6% and 11.3% for optimum and reduced moisture conditions, respectively. These results encourage further use of T1BL.1RS
wheats in improving agronomic traits, especially for reduced irrigation or rainfed environments.
It has been hypothesised that wheat yields may be increased by lengthening the duration of the stemelongation phase. This
paper reports studies on the effects of chromosomes carrying major photoperiod genes (Ppd-A1, Ppd-B1, Ppd-D1) in different genetic backgrounds, on responses to photoperiod before and after jointing, when the onset of stem elongation
occurs, and on number of grains per spike. A field experiment considered the effects of two photoperiods on Chinese Spring
and 12 substitution lines, in which chromosomes 2A, 2B or 2D had been substituted by those from four contrasting cultivars.
The phase from seedling emergence to jointing (EM-JO) was more responsive than that from jointing to anthesis (JO-ANT), but
no relationship was found between the duration of these phases. EM-JO length affected leaf and spikelet number and consequently
grains per spike, but this component was further influenced by JO-ANT duration. Our results confirmed that the phases are
independent in sensitivity, supporting the hypothesis that genetic manipulation of phase duration could enhance yield, but
no evidence was found of any particular Ppd allele being responsible for major responses to photoperiod during stem elongation.
Investigations of the world wheat genepool conducted by Ukraine's National Centre for Plant Genetic Resources produced information
on the geographic origins and genetic background of numerous wheat lines possessing the 1BL/1RS wheat-rye translocation, 1B(R)
substitution and 1AL/1RS translocation. Wheat-rye translocations can determine high productivity, adaptive possibilities,
and disease and insect resistance in wheat. Data on 330 cultivars and lines carrying wheat-rye translocations and/or substitutions
were analysed. Based on this information, wheats were classified according to continent and country of origin and year of
release. This clarified how translocation sources of different genetic and geographic origins have been used in breeding programmes
all over the world.
The understanding of the changes produced by plant breeding on wheat grain yield and on its determinants, through the study of the behaviour of cultivars released at different times during the breeding process, could be a useful tool to define future selection criteria. The aim of this paper was to examine the genetic improvement effects on bread wheat grain yield potential and on its major physiological determinants in different countries.
Generally, it seems that the genetic improvement produced important increases in harvest index, but it did not produce important changes in total biomass. The genetic gain in grain yield ranged from 0.58 g m-2 year-1 (India) to 5.84 g m-2 year-1 (Mexico); reflecting important differences among genetic improvement programmes. However, when the comparisons were made in relative values, the difference was much lower, ranging from 0.16% year-1 to 0.90% year-1, for the previously mentioned countries, respectively. Most of the regions showed relative genetic gains of around 0.45% year-1. Similar patterns of relative genetic gains in harvest index were found.
Half of the total gain in grain yield in the past was due to genetic gain in grain yield potential. However, it is expected for the future, that further increases in grain yield will rely more on genetic gain than on technologic gain. Thus, a discussion about possible strategies in future breeding programmes of bread wheat is attempted throughout the paper.
The changes in grain yield were mostly associated with changes in number of grains per m2 rather than with changes in individual grain weight. It appears that the source: sink ratio during the grain-filling period was very high in old cultivars, whereas the source: sink ratio in modern cultivars is more balanced. Further increases in number of grains m-2 could be compensated by a reduction in individual grain weight, if simultaneous improvement in source strength during grain-filling is not achieved.
The crop attributes which have been changed together with the mentioned traits are discussed and alternative selection criteria are suggested.
Triticum tauschii (Coss.) Schmalh. (Aegilops squarrosa auct. non L., 2n=2x=14, DD genome) with its diverse range of accessions and distribution provides a unique opportunity for exploiting novel genetic variability for wheat (T. aestivum L.) improvement associated with biotic/abiotic stress factors. From our working collection of 490 T. tauschii accessions we have so far produced 430 different synthetic hexaploids (2n=6x=42, AABBDD) resulting from the chromosome doubling of Triticum turgidum L. s. lat. x T. tauschii F1 hybrids (each synthetic involving a different T. tauschii accession). We present here our results on hybrid production, plantlet regeneration, cytology, colchicine induced doubling of the 2n=3x=21 chromosome F1 hybrids, seed increase of the doubled progeny and screening for a biotic stress; Cochliobolus sativus Ito and Kuribay (syn. Helminthosporium sativum Pamm. King and Bakke); of 250 of these synthetic hexaploid (2n=6x=42) amphiploids. Application of the direct crossing methodology involving susceptible T. aestivum cultivars with resistant T. tauschii accessions is also alluded to.