No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Patterns for Pea-Rhizobium symbiosis efficiency response to pedological and varietal variations in Tunisia
Abstract
Pedological constrains and varietal recommendations are serious causes of Pea-Rhizobium symbiosis efficiency deviations in Tunisia limiting pea crop adaptation to varying environments. In order to explore variation patterns of this symbiosis in contrasting soils and varieties and appreciate its contribution to plant adaptation, nine locations with potential pea crop vocation are prospected for collection of soils. Two pea varieties with different cycle length are randomly sown on triplicate irrigated containers and placed on natural condition during two seasons. The results have shown that soil fertility is mostly low and highly variable. It is mainly affected by high active limestone content and pH or by salinity. The studied factors (Soil type, Variety) have presented highly significant effect on native rhizobia efficiency, pea root nodulation, shoot and root biomass production, and shoot nitrogen accumulation (p < 0.0001). The long cycle variety gave the highest nodulation and adaptability to pedological variations. The multivariate data analysis indicates that Pea-Rhizobium symbiosis efficiency variability is mainly due to soil microbial biomass, phosphorus, organic matter, and electrical conductivity differences between soils. However, Principal Coordinate Analysis has confirmed the determining effect of these variables on rhizobia effectiveness, pea nodulation, growth and nitrogen accumulation. These results confirm that nitrogen-fixing symbiosis does not contribute in adaptation of pea crop to pedological constrains in Tunisia. Rhizobial inoculation and sepecific fertilization managment have become an urgent need to improve the production of this crop.
... Pea is one of the first domesticated crops, and it contributes to sustainable agriculture by playing important agronomic, economic, and environmental roles [27]. It is an alternative cover crop in semi-arid regions, capable of generating an economic return due to grain production [27]. ...
... Pea is one of the first domesticated crops, and it contributes to sustainable agriculture by playing important agronomic, economic, and environmental roles [27]. It is an alternative cover crop in semi-arid regions, capable of generating an economic return due to grain production [27]. The co-inoculation between PGPR and the Rlv strain has shown some promising results in pea. ...
Pulses provide distinct health benefits due to their low fat content and high protein and fiber contents. Their grain production reaches approximately 93,210 × 103 tons per year. Pulses benefit from the symbiosis with atmospheric N2-fixing bacteria, which increases productivity and reduces the need for N fertilizers, thus contributing to mitigation of environmental impact mitigation. Additionally, the root region harbors a rich microbial community with multiple traits related to plant growth promotion, such as nutrient increase and tolerance enhancement to abiotic or biotic stresses. We reviewed the eight most common pulses accounting for almost 90% of world production: common beans, chickpeas, peas, cowpeas, mung beans, lentils, broad beans, and pigeon peas. We focused on updated information considering both single-rhizobial inoculation and co-inoculation with plant growth-promoting rhizobacteria. We found approximately 80 microbial taxa with PGPR traits, mainly Bacillus sp., B. subtilis, Pseudomonas sp., P. fluorescens, and arbuscular mycorrhizal fungi, and that contributed to improve plant growth and yield under different conditions. In addition, new data on root, nodule, rhizosphere, and seed microbiomes point to strategies that can be used to design new generations of biofertilizers, highlighting the importance of microorganisms for productive pulse systems.
... sativum) is grown over about 20 000 ha and is widely distributed across southern and Northern grain production regions, particularly in lower rainfall climates. However, until 2016, pea cultivated areas showed a decline by 30%, presenting only 13% of the total Tunisian grain legumes area (MARHP 2017) with very low yields (7.2 t/ha) (Hachana et al. 2021). ...
... Therefore, it is of interest to characterize a wider variety of bacterial strains as potential inoculants since only R. leguminosarum isolated from pea has been described to date. It is also significant to pull through the limiting pea yields problems in Tunisia in relation to the low efficiency of native LNB strains adapted to Tunisian soil constraints (Hachana et al. 2021). ...
Eighty-four Pisum sativum legume nodulating bacteria (LNB) were isolated from seven geographical sites from southern Tunisia. Phylogenetic analyses based on partial sequences of 16S rRNA gene and the housekeeping genes glnII, and recA grouped strains into six clusters, four of which belonged to the genus Rhizobium and two to the Ensifer genus. Among Rhizobium clusters, 41 strains were affiliated to Rhizobium leguminosarum, two strains to R. pisi, two strains to R. etli, and interestingly two strains belonged to previously undescribed Rhizobium species. The remaining two strains were closely related to Ensifer medicae (two strains) and Ensifer meliloti (two strains). A symbiotic nodC gene-based phylogeny and host specificity test showed that all Rhizobium strains nodulating pea belonged to the symbiovar viciae, whereas the Ensifer strains were associated with the symbiovar meliloti never described to date. All strains under investigation differed in the number of induced root nodules and the effectiveness of atmospheric nitrogen fixation. The R. leguminosarum PsZA23, R. leguminosarum PsGBL42 and E. medicae PsTA22a, forming the most effective symbiosis with the plant host, are potential candidates for inoculation programs.
... The biotic elicitor (e.g. algae, fungi, bacteria and plant extracts) plays a major role in controlling diseases through induced resistance [36][37][38][39][40]. Rhizobia have been used when dealing with bacteria in bio-fertilization [41][42][43], broomrape parasitism management [15][16][17]37] and biological pathogen control [44]. ...
In Tunisia, Orobanche foetida Poir. is considered an important agricultural biotic constraint on faba bean (Vicia faba L.) production. An innovative control method for managing this weed in faba bean is induced resistance through inoculation by rhizobia strains. In this study, we explored the biochemical dynamics in V. faba L. minor inoculated by rhizobia in response to O. foetida parasitism. A systemic induced resistant reaction was evaluated through an assay of peroxidase (POX), polyphenol oxidase (PPO) and phenyl alanine ammonialyase (PAL) activity and phenolic compound and hydrogen peroxide (H2O2) accumulation in faba bean plants infested with O. foetida and inoculated with rhizobia. Two rhizobia strains (Mat, Bj1) and a susceptible variety of cultivar Badi were used in a co-culture Petri dish experiment. We found that Mat inoculation significantly decreased O. foetida germination and the number of tubercles on the faba bean roots by 87% and 88%, respectively. Following Bj1 inoculation, significant decreases were only observed in O. foetida germination (62%). In addition, Mat and Bj1 inoculation induced a delay in tubercle formation (two weeks) and necrosis in the attached tubercles (12.50% and 4.16%, respectively) compared to the infested control. The resistance of V. faba to O. foetida following Mat strain inoculation was mainly associated with a relatively more efficient enzymatic antioxidative response. The antioxidant enzyme activity was enhanced following Mat inoculation of the infected faba bean plant. Indeed, increases of 45%, 67% and 86% were recorded in the POX, PPO and PAL activity, respectively. Improvements of 56% and 12% were also observed in the soluble phenolic and H2O2 contents. Regarding inoculation with the Bj1 strain, significant increases were only observed in soluble phenolic and H2O2 contents and PPO activity (especially at 45 days after inoculation) compared to the infested control. These results imply that inoculation with the rhizobia strains (especially Mat) induced resistance and could bio-protect V. faba against O. foetida parasitism by inducing systemic resistance, although complete protectionwas not achieved by rhizobia inoculation. The Mat strain could be used as a potential candidate for the development of an integrated method for controlling O. foetida parasitism in faba bean.
There is considerable evidence that abiotic factors have an important influence on the microbial diversity of natural ecosystems. In the present study, we tested the hypothesis that rhizospheric and endophytic micro-organisms isolated from the roots of Hymenaea courbaril L. in two biomes with distinct ecological characteristics – the Pantanal wetland and the Cerrado savanna – present distinct functional traits. We also evaluated the functional diversity (H’) of the microbiota and the potential effects of soil parameters, such as Organic Material (OM), cation exchange capacity (CEC), and nutrient concentrations, on the relative abundance of the micro-organisms with functional traits such as the solubilization of phosphates (CaHPO4, AlPO4, and FePO4), the synthesis of indole-3-acetic acid (IAA) and the ACC deaminase enzyme, and antibiosis to the phytopathogens Fusarium sp., Sclerotinia sclerotiorum, and Rhizoctonia sp. A higher percentage of the micro-organisms from the Pantanal (in comparison with the Cerrado) presented intense or very intense function in the synthesis of IAA and antibiosis, with a higher degree of specialization (reduced functional diversity) in the former trait (H’ = 0.73) and a lower degree in the latter (H’ = 0.91 for antibiosis to Fusarium sp.; H’ = 0.97 for S. sclerotiorum, and H’ = 0.80 for Rhizoctonia sp.). The micro-organisms of the Cerrado were more effective in the solubilization of phosphates, and the mean concentrations of P solubilized by these micro-organisms were higher than those observed in the isolates from the Pantanal, when the sources were AlPO4 and FePO4, which indicates a potential relationship between the high concentrations of Al and Fe found naturally in the soils of the Cerrado and the functional traits of its endemic microbiota. We also observed high levels of diversity in the functional traits of the Cerrado micro-organisms involved in solubilization (H’ = 1.09 for CaHPO4, H’ = 1.05 for AlPO4, and H’ = 1.09 for FePO4). All the isolates from both biomes synthetized ACC deaminase very intensively. In the Pantanal, soil parameters such as pH, OM, CEC, and the levels of Mn and Fe, as well as the Fe concentrations in the root and aerial portion of the plant affected the relative abundance of the micro-organisms that had efficient functional traits. In the Cerrado soil, the parameters pH, CEC, and the Mn, Mg, and Fe concentrations, as well as the level of Fe in the aerial part of the plant all affected the relative abundance. We proved our hypothesis on the specialization of the micro-organisms for specific functional traits, and also that the functionality of the symbiotic microbiota is influenced by environmental parameters. The present study provides important insights into the interactions between the soil and the endophytic root and rhizospheric micro-organisms isolated from H. courbaril L. in the Pantanal and Cerrado biomes. These findings will support future studies that will better define the environmental factors that influence the expression of different functional traits by the micro-organisms in the microbiome.
Rhizobia–legume symbiosis is an important type of plant–microbe mutualism; however, the establishment of this association is complicated and can be affected by many factors. The soybean rhizosphere has a specific microbial community, yet whether these organisms affect rhizobial nodulation has not been well investigated. Here, we analyzed the compositions and relationships of soybean rhizocompartment microbiota in three types of soil. First, we found that the rhizosphere community composition of soybean varied significantly in different soils, and the association network between rhizobia and other rhizosphere bacteria was examined. Second, we found that some rhizosphere microbes were correlated with the composition of bradyrhizobia and sinorhizobia in nodules. We cultivated 278 candidate Bacillus isolates from alkaline soil. Finally, interaction and nodulation assays showed that the Bacillus cereus group specifically promotes and suppresses the growth of sinorhizobia and bradyrhizobia, respectively, and alleviates the effects of saline–alkali conditions on the nodulation of sinorhizobia as well as affecting its colonization in nodules. Our findings demonstrate a crucial role of the bacterial microbiota in shaping rhizobia–host interactions in soybean, and provide a framework for improving the symbiotic efficiency of this system of mutualism through the use of synthetic bacterial communities.
The aim of the paper was to determine the effects of environmental factors and soil fertilizers (Universol Blue and Ferticare I, applied for 3 weeks), upon production parameters of garden pea (Pisum sativum). In this regard, there were analysed: soil pH and soil temperature at the moment of sowing. The garden pea, Bördi variety, was randomly sown in early April, on 18 plots, which formed 6 experimental variants (three plots on variant). First variant V1 was the control. Variants V2, V3 and V4 have been fertilised with Universol Blue (337.5g; 421.875g; 506.25 g/variant), and V5, V6 have been fertilised with Ferticare I (540g; 607.5g/variant). After harvesting, there were determined the statistical estimates of the peashells number/variant, estimates of total peashells weight/variant and individual peashells weight/variant. The results showed that soil pH values were in the weak acid range, pH of variants V2, V3 and V4 being slightly more acidic (6.59) than pH of V5 and V6. Soil temperatures was between 6 0 and 7 0 C all over the plots. The number of peashells was increased in all variants, relative to the control (control and V3 exhibited a high variability 26.12%, respectively 21.77%). Ferticare I fertilizer was more effective than Universol Blue (938.17 vs. 907.89 peashells). The t values were insignificant between variants, concerning most parameters. The evolution of pH to alkaline domain and the increase in soil temperature, favored the increase in the total weight of peashells (r=0.789*, respectively r=0.882*). Fertilization have reduced the variability, caused by environmental conditions. The application of fertilizers did not increase the weight of peashells, but increased the total number of peashells.
Cultivar recommendation based on mean performance determined by multi-environment trials (METs) conducted on research stations could be unreliable and ineffective for assessing performance in farmers' fields. It is important to improve the efficiency of cultivar recommendation based on METs. For this purpose, it would be useful to validate recommendations based on yield data obtained directly from farmers, i.e., through surveys. The aim of this study was to discuss the possibility and statistical methodology of assessing cultivar performance patterns based on yield data obtained through farmer surveys. We suggest that this might be accomplished by assessing the conformity of yield ranking and yield performance patterns between MET and survey datasets in the same growing regions. As an example, we compare winter wheat (Triticum aestivum L.) yield data obtained from Polish farmers via surveys with data obtained via METs. In the METs, cultivars were evaluated at two levels of crop-management, a moderate-input management (MIM) system and a high-input management (HIM) system. Based on the yield evaluations in the current study, half of the agro-ecological regions had relatively high levels of consistency in yield rankings between the MET MIM system and survey yield dataset. This indicated a relatively high efficiency of cultivar recommendations based on METs in these regions, especially for the MIM system. For the HIM system, however, with the exception of one region, we observed a poor degree of consistency in cultivar ranking.
The pea (Pisum sativum L.) is arguably an important winter pulse crop and a fundamental source of proteins for human and animal nutrition. In Tunisia, pea cultivation is characterized by its instability, especially in the arid region of Southern Tunisia. We carried out an investigation of the agro-morphological and genetic diversity of 12 local pea accessions cultivated in the arid region. We analyzed 21 qualitative and 26 quantitative traits following the UPOV descriptors. Furthermore, 8 SSRs were employed to examine genetic polymorphism, differentiation, and population structure. Molecular and agro-morphological data distinguished all the accessions under investigation. A considerable phenotypic diversity among accessions was observed for many characters, including some related to agronomical performance. At the molecular level, all the SSRs were polymorphic, with an average of 0.44 PIC value per locus. Our work indicated the presence of a wide-ranging variation among the local pea accessions evaluated. The overall results indicated that the agro-morphological traits and SSR markers were reliable and effective for assessing the genetic diversity of phenotypic pea accessions.
Members of the plant family Leguminosae (Fabaceae) are unique in that they have evolved a symbiotic relationship with rhizobia (a group of soil bacteria that can fix atmospheric nitrogen). Rhizobia infect and form root nodules on their specific host plants before differentiating into bacteroids, the symbiotic form of rhizobia. This complex relationship involves the supply of C4-dicarboxylate and phosphate by the host plants to the microsymbionts that utilize them in the energy-intensive process of fixing atmospheric nitrogen into ammonium, which is in turn made available to the host plants as a source of nitrogen, a macronutrient for growth. Although nitrogen-fixing bacteroids are no longer growing, they are metabolically active. The symbiotic process is complex and tightly regulated by both the host plants and the bacteroids. The metabolic pathways of carbon, nitrogen, and phosphate are heavily regulated in the host plants, as they need to strike a fine balance between satisfying their own needs as well as those of the microsymbionts. A network of transporters for the various metabolites are responsible for the trafficking of these essential molecules between the two partners through the symbiosome membrane (plant-derived membrane surrounding the bacteroid), and these are in turn regulated by various transcription factors that control their expressions under different environmental conditions. Understanding this complex process of symbiotic nitrogen fixation is vital in promoting sustainable agriculture and enhancing soil fertility.
Pea forms symbiotic nodules with Rhizobium leguminosarum sv. viciae (Rlv). In the field, pea roots can be exposed to multiple compatible Rlv strains. Little is known about the mechanisms underlying the competitiveness for nodulation of Rlv strains and the ability of pea to choose between diverse compatible Rlv strains. The variability of pea-Rlv partner choice was investigated by co-inoculation with a mixture of five diverse Rlv strains of a 104-pea collection representative of the variability encountered in the genus Pisum. The nitrogen fixation efficiency conferred by each strain was determined in additional mono-inoculation experiments on a subset of 18 pea lines displaying contrasted Rlv choice. Differences in Rlv choice were observed within the pea collection according to their genetic or geographical diversities. The competitiveness for nodulation of a given pea-Rlv association evaluated in the multi-inoculated experiment was poorly correlated with its nitrogen fixation efficiency determined in mono-inoculation. Both plant and bacterial genetic determinants contribute to pea-Rlv partner choice. No evidence was found for co-selection of competitiveness for nodulation and nitrogen fixation efficiency. Plant and inoculant for an improved symbiotic association in the field must be selected not only on nitrogen fixation efficiency but also for competitiveness for nodulation.
Continuous cereal-based cropping has led to a rapid decline in soil fertility in the Guinea savanna agro-ecological zone of northern Ghana with corresponding low crop yields. We evaluated the effects of cropping system and soil fertility status on grain yields and N2-fixation by grain legumes and net N contribution to soil fertility improvement in contrasting sites in this agro-ecological zone. Maize was intercropped with cowpea, soybean and groundnut within a row, with a maize stand alternated with two equally spaced cowpea or groundnut stands and in the maize-soybean system, four equally spaced soybean stands. These intercrops were compared with sole crops of maize, cowpea, soybean and groundnut in fertile and poorly fertile fields at sites in the southern (SGS) and the northern (NGS) Guinea savanna. The proportion of N derived from N2-fixation (%Ndfa) was comparable between intercrops and sole crops. However, the amount of N2-fixed was significantly larger in sole crops due to a greater biomass accumulation. Legumes in poorly fertile fields had significantly smaller shoot δ 15N enrichment (-2.8 to +0.7‰) and a larger %Ndfa (55-94%) than those in fertile fields (-0.8 to +2.2‰; 23-85%). The N2-fixed however was larger in fertile fields (16-145kgNha-1) than in poorly fertile fields (15-123kgNha-1) due to greater shoot dry matter and N yields. The legumes grown in the NGS obtained more of their N requirements from atmospheric N2-fixation (73-88%) than legumes grown in the SGS (41-69%). The partial soil N balance (inkgha-1) was comparable between intercrops (-14 to 21) and sole legumes (-8 to 23) but smaller than that of sole maize receiving N fertiliser (+7 to +34). With other N inputs (aerial deposition) and outputs (leaching and gaseous losses) unaccounted for, there is uncertainty surrounding the actual amount of soil N balances of the cropping systems, indicating that partial N balances are not reliable indicators of the sustainability of cropping systems. Nevertheless, the systems with legumes seem more attractive due to several non-N benefits. Our results suggest that soybean could be targeted in the SGS and cowpea in the NGS for greater productivity while groundnut is suited to both environments. Grain legumes grown in poorly fertile fields contributed more net N to the soil but growing legumes in fertile fields seems more lucrative due to greater grain and stover yields and non-N benefits.
The complimentary effects of a native rhizobia strain (SAMFIX 286), lime and single superphosphate (SSP) as components of ISFM were evaluated on the biomass, nodulation and N2 fixation of cowpea (Vigna unguiculata L.). Lime was applied at the rate of 250 kg (Ca(OH)2) ha−1, while SSP was applied at 30 kg P ha−1. The trial was carried out in a screen house with the treatments arranged in randomized complete block design. Results obtained show that the performance of SAMFIX 286 inoculated plants did not significantly (p < 0.05) differ from that of the un-inoculated treatment. Application of lime significantly increased root dry weight, shoot dry weight, nodule number and dry weight by 42.5%, 35.3%, 65.6% and 50%, respectively. Nodulation was significantly (p < 0.05) increased by SSP. The complimentary effect of lime with SSP significantly increased total shoot N concentration. Similarly, combined inoculation of SAMFIX 286 with lime and SSP increased N concentration by 31.9% and N derived from atmosphere (Ndfa) by 16.3% compared to the un-inoculated treatment. Inoculation of SAMFIX 286 with SSP was also effective on Ndfa by cowpea. It was concluded that lime and SSP were good combination with native rhizobia strain in improving cowpea nodulation and biological N2 fixation.
For farmers, pea crop is characterized by a large yield variability between years, between areas, and even between fields in a same small area in a given year. In dry year, spring pea crops are mostly affected by water stress and high temperature but significant yield losses can also be caused by a root disease, Aphanomyces euteiches, particularly during wet years. Winter pea can escape partially from drought, high temperature, and root disease during the reproductive phase of the crop cycle. However, when winters are mild, without progressive negative temperatures, which provide frost acclimation, available cultivars are not resistant enough to frost and are susceptible to aerial diseases such as ascochyta blight and bacterial blight (Pseudomonas syringae pv. pisi), thus leading to yield losses. A better adaptation of sowing dates, an improvement of lodging resistance and a limitation of the sowing density can limit the development of ascochyta blight for winter pea crops. For spring pea, an increased use of Aphanomyces soil test could avoid to sow the crop in infested fields. Current spring pea varieties are the result of changes in plant architecture including the reduction of 1000-seed weight that have led to yield losses by increasing the fragility of variety facing these stresses. The development of a pea crop model, simulating the effect of various stress encountered on winter and spring pea crops, can help to better define the regions adapted for the production of these two types of cultivars, and also help the breeders to better define and choose which trait to improve in order to increase the pea productivity and yield stability. National and European projects are in course to breed new varieties more adapted to different stresses.
The growth, development and yield of chickpea (Cicer ariеtinum L.) is strongly influenced by abiotic factors such as salinity and drought in the arid conditions. The use of efficient plant growth promoting bacteria in chickpea production is the best solution to overcome those stresses. In the present study, 10 chickpea rhizobial strains were isolated and purified from the nodules of chickpea genotype grown on middle salinated soils with different chickpea cultivation histories, 3 of them were more efficient in salt tolerance and showed higher nodulation abilities. Local chickpea genotype Uzbekistan-32 was inoculated with selected Rhizobium bacterial strains before planting them to the field condition. Inoculation of plants with strains Rhizobium sp. R4, R6 and R9 significantly increased shoot, root dry matter, and nodule number by 17, 12, and 20% above the uninoculated plants, respectively. The shoot length increased by 52%, root length by 43%, shoot dry weight by 36%, and root dry weight by 64%. Inoculation significantly increased the pod number by 28% and yield up to 55% as compared to control plant. The effective indigenous rhizobial strains isolated in this study from chickpeas on middle salinated soils of Uzbekistan have the characters of broad host range, high nodulation efficiency, efficient N fixation, great salt tolerance. Soil nitrogen, phosphorus and carbon content of the soil at the end of experiments were positive in all the treatments compare control. In this study, we are focused with consideration of the relationship between chickpea and its symbiotic nitrogen-fixing root nodule bacterial strains and how it functions to influence plant productivity and soil fertility.
The soil organic matter content is an important characteristic of soils fertility. It is also a characteristic more and more wanted in a global context of climate change, where the storage of the carbon in soil is a serious alternative to limit the CO2 emissions into atmosphere. Thirty-five soils located in North Tunisia (25 cultivated soils and 10 forest soils) were sampled. Soil organic matter was characterized by measuring total organic carbon content and total nitrogen content and the biodegradability of soil organic matter determinated by measuring the microbial respiration during 28 days of incubation at 28°C. The soil organic carbon content and total nitrogen content of the studied soils vary from 0.8 to 3.2% and from 0.07 to 0.45%, respectively. The forest soils have the largest contents in carbon and in nitrogen. At the end of the incubations, the quantity of C-CO2 emitted by the 35 soils varies between 213 and 853 mg C-CO2.kg-1 dry soil. The easy mineralizable pool varies between 1.6 and 7.6% of the total organic carbon of soils. The quantity of resistant carbon was estimated by means of the Van't Hoff law; it varies between 92 and 99% of the total soil organic carbon.
Based on their performance attributes, butter bean (variety Ex-kasuku) and grass pea (Selection 1325) have been identified as potential alternative legumes for the maize-based cropping system in the cold semi-arid region of Laikipia County in Kenya. However, their nitrogen fixation potential and nitrogen residual effects have not been established. A green house experiment was therefore conducted to determine the nitrogen fixation potential and residual effects of the introduced legumes (butter bean and grasspea) relative to the local checks (common bean cv. Katumani 330 and chickpea cv. Desi). The legume seeds were planted in perforated polythene bags, measuring 14 cm diameter and 20 cm high, containing 3.6 kg air dried soil collected from Matanya in Laikipia County, Kenya. Barley, a non-nitrogen fixing reference crop, was also planted in polythene bags and used to determine the amount of nitrogen fixed according the N-difference method. Butter bean and grass pea significantly out-performed chickpea in total nodule number, active nodule number, total nodule dry matter, total plant dry matter, dry matter N yield, amount of N-fixed, percent N derived from the atmosphere and residual N effect, but were comparable to common bean in all these attributes. There was a significant, positive linear relationship between quantity of N-fixed and quantity of total plant biomass accumulated. Butter bean, grass pea and common bean significantly increased soil mineral nitrogen while chickpea had no influence on soil nitrogen. Butter bean and grasspea can therefore provide N to cropping systems in the cold semiarid region through biological N fixation.
Little information currently exists on the relationship between rhizobial symbiosis and mineral accumulation in nodulated legumes. The aim of this study was to measure fixed nitrogen (N) in whole plants and in young fully expanded trifoliate leaves of cowpea genotypes, and to relate this to mineral accumulation in the leaves. The data revealed marked differences between high and low N-2-fixing genotypes, with the former consistently showing greater %N, plant or leaf total N, and amount of N fixed compared with the latter. There was a 2.0-3.8-fold difference in amount of N fixed at whole-plant level between high- and low-fixing cowpea genotypes at Taung, South Africa, and 2.4-4.0-fold at Manga, Ghana. Furthermore, the genotypes with high N-2 fixation consistently exhibited greater concentration and content of minerals (e.g. P, K, Mg, S, Na, Fe, Cu, Zn, Mn and B) in their trifoliate leaves, whereas those that recorded low N-2 fixation accumulated lesser amounts of mineral nutrients in leaves. In a nodulation assay, we found that rhizobial isolates TUT53b2vu and TUT33b4vu, which exhibited higher symbiotic efficiency (measured here as nodule number, nodule fresh weight, and plant dry matter yield), also elicited greater mineral accumulation in cowpea shoots, while strains with low N-2-fixing ability induced limited mineral accumulation. These results, together with a correlation analysis, show that, at least in nodulated cowpea, there is a strong relationship between N-2-fixing efficiency and mineral accumulation, two traits that could be exploited in breeding programs for improved human nutrition and health.
Effect of low temperature, salinity, nutrient level and photoperiod has been studied on 3 varieties of Pisum sativum var., P-48, meteor and AM-1inoculated with Rhizobium strain PS-1. The plants were grown at 5, 10, 15, 20 and 25 o C. The number of viable rhizobial cells was counted at each temperature by most probable number technique. The number of viable cells were constant at 5 and 10 o C but increased between 15-30 o C. Nodule formation was not observed at 5, 10 and 25 o C at 15 o C the nodules were less in number, whereas at 20 o C best nodulation was observed. The pea plants were also subjected to different salinity levels i.e., 0, 1, 2, 3, 4, 5, 10 and 15dsm -1 . High number of nodules was formed at 0 and 1dsm -1 whereas at 2 and 3dsm -1 the nodule number was reduced and yet at higher salinity levels no nodules were formed. Pea plants nodulated best at 12 hours photoperiod and 1/6 th concentration of Hoagland's nutrient solutions. The mature nodules developed at different temperatures and salinity levels were assayed for nitrogenase activity and processed for light and electron microscopy which supported our study.
Regular soil testing is an important element in nutrient management. You can use soil tests as a diagnostic tool or to identify trends through time. To obtain meaningful test results, you must sample soil correctly, at the same time each year, and you must maintain records.
The design of fertilization plans to cover large areas is complex, due to the considerable number of soil samples and soil fertility variables that must be taken into account. Classifying forest stands in groups according to their soil fertility (i.e. in nutrient management areas) can be very helpful to this respect and it is considered to be a first step in what has been called precision forestry. For this paper, we explore the capability of multivariate analyses of topsoil data to be used as tools for evaluating and classifying soil fertility. A case study from a teak (Tectona grandis L.f.) plantation in Costa Rica was used to evaluate and illustrate how to use multivariate analysis with these aims. A topsoil (0–20 cm) database with soil test results assembled by Panamerican Woods Ltd. was used. Different multivariate techniques [Principal Component Analysis, Non-metric Multidimensional Scaling (NMDS), Cluster analysis] were performed and compared. Cluster analysis resulted as an appropriate tool for grouping soil samples into soil fertility classes. Therefore, it is considered as a promising tool which would help to design a fertilization program to meet the specific needs of each group of stands with relatively homogeneous soil fertility properties. NMDS is also a suitable complementary tool to graphically explore the similarities within groups and the differences between them. The application of procedures similar to those being reported may help to optimize the design of nutritional and fertilization plans across large forest plantations, by using multivariate analysis to establish fertilization regimes that are appropriate to groups of stands of more homogeneous soil fertility.
As a major contributor to the reduced nitrogen pool in the biosphere, symbiotic nitrogen fixation by legumes plays a critical role in a sustainable production system. However this legume contribution varies with the physico-chemical and biological conditions of the nodulated-root rhizosphere. In order to assess the abiotic and biotic constrains that might limit this symbiosis at the agroecosystem level, a nodular diagnosis is proposed with common bean as a model grain-legume, and a major source of plant proteins for world human nutrition. The engineering of the legume symbiosis is addressed by participatory assessment of bean recombinant inbred lines contrasting for their efficiency in use of phosphorous for symbiotic nitrogen fixation. With this methodology, in field-sites chosen with farmers of an area of cereal-cropping in the Mediterranean basin, a large spatial and temporal variation in the legume nodulation was found. Soil P availability was a major limiting factor of the rhizobial symbiosis. In order to relate the field measurements with progress in functional genomics of the symbiosis, in situ RT-PCR on nodule sections has been implemented showing that the phytase gene is expressed in the cortex with significantly higher number of transcripts in P-efficient RILs. It is concluded that various tools and indicators are available for developing the ecological engineering of the rhizobial symbiosis, in particular for its beneficial contribution to the bio-geochemical cycle of N, and also P and C.
Alley cropping is being widely tested in the tropics for its potential to sustain adequate food production with low agricultural inputs, while conserving the resource base. Fast growth and N yield of most trees used as hedgerows in alley cropping is due greatly to their ability to fix N2 symbolically with Rhizobium. Measurements of biological N2 fixation (BNF) in alley cropping systems show that some tree species such as Leucaena leucocephala, Gliricidia
sepium and Acacia mangium can derive between 100 and 300 kg N ha−1 yr−1 from atmospheric N2, while species such as Faidherbia albida and Acacia Senegal might fix less than 20 kg N ha−1 yr−1. Other tree species such as Senna siamea and S. spectabilis are also used in alley cropping, although they do not nodulate and therefore do not fix N2. The long-term evaluation of the potential or actual amounts of N2 fixed in trees however, poses problems that are associated with their perennial nature and massive size, the great difficulty in obtaining representative samples and applying reliable methodologies for measuring N2 fixed. Strategies for obtaining representative samples (as against the whole tree or destructive plant sampling), the application of 15N procedures and the selection criteria for appropriate reference plants have been discussed.
Little is known about the effect of environmental factors and management practices such as tree cutting or pruning and residue management on BNF and eventually their N contribution in alley cropping. Data using the 15N labelling techniques have indicated that up to 50% or more of the tree’s N may be below ground after pruning. In this case, quantification of N2 fixed that disregards roots, nodules and crowns would result in serious errors and the amount of N2 fixed may be largely underestimated. Large quantities of N are harvested with hedgerow prunings (> 300 kg N ha−1 yr−1) but N contribution to crops is commonly in the range of 40–70 kg N ha−1 season. This represents about 30% of N applied as prunings; however, N recoveries as low as 5–10% have been reported. The low N recovery in maize (Zea mays) is partly caused by lack of synchronization between the hedgerow trees N release and the associated food crop N demand. The N not taken up by the associated crop can be immobilized in soil organic matter or assimilated by the hedgerow trees and thus remain in the system. This N can also be lost from the system through denitrification, volatilization or is leached beyond the rooting zone. Below ground contribution (from root turnover and nodule decay) to an associated food crop in alley cropping is estimated at about 25–102 kg N ha−1 season−1. Timing and severity of pruning may allow for some management of underground transfer of fixed N2 to associated crops. However many aspects of root dynamics in alley cropping systems are poorly understood. Current research projects based on 15N labelling techniques or 15N natural abundance measurements are outlined. These would lead to estimates of N2 fixation and N saving resulting from the management of N2 fixation in alley cropping systems.
Legume-based cropping systems have the potential to internally regulate N cycling due to the suppressive effect of soil N availability on biological nitrogen fixation. We used a gradient of endogenous soil N levels resulting from different management legacies and soil textures to investigate the effects of soil organic matter dynamics and N availability on soybean (Glycine max) N₂ fixation. Soybean N₂ fixation was estimated on 13 grain farm fields in central New York State by the ¹⁵N natural abundance method using a non-nodulating soybean reference. A range of soil N fractions were measured to span the continuum from labile to more recalcitrant N pools. Soybean reliance on N₂ fixation ranged from 36% to 82% and total N₂ fixed in aboveground biomass ranged from 40 to 224 kg N ha⁻¹. Soil N pools were consistently inversely correlated with % N from fixation and the correlation was statistically significant for inorganic N and occluded particulate organic matter N. However, we also found that soil N uptake by N₂-fixing soybeans relative to the non-nodulating isoline increased as soil N decreased, suggesting that N₂ fixation increased soil N scavenging in low fertility fields. We found weak evidence for internal regulation of N₂ fixation, because the inhibitory effects of soil N availability were secondary to the environmental and site characteristics, such as soil texture and corresponding soil characteristics that vary with texture, which affected soybean biomass, total N₂ fixation, and net N balance.
A phenetic analysis showed that peas from Afghanistan which are resistant to nodulation by European strains of Rhizobium leguminosarum form a close-knit group. They are quite distinct from susceptible lines found in Afghanistan, which are much more diverse and show a range of variation almost as extensive as a world-wide sample. The resistant peas possess a number of distinctive features, including small flowers, small pods and brown-marbled seeds. A high proportion are also resistant to powdery mildew (Erysiphe polygoni). They were collected over a wide area of Afghanistan, and a Rhizobium-resistant line from Israel is also very similar. Limited evidence suggests that resistant and susceptible varieties may coexist throughout the area from Israel to Afghanistan, and that “universal” Rhizobium strains, able to nodulate resistant plants, may have a similar range. However, both resistance and universal strains were left behind when pea cultivation spread north into Europe.
Plants are exposed to different kinds of adverse environmental conditions during their life cycle that ablate their productivity. These environmental fluctuations have detrimental effects on the crops in terms of growth and development. Plants are highly susceptible to abiotic stresses including drought, salinity, high temperature, and increasing heavy metal concentration. The changing events related to climatic conditions are the signs of consternation for crops to maintain their productivity. Due to global warming, drought and high temperature are serious concerns regarding effective crop production. Salinity also adversely affects growth and productivity by disrupting normal physiology and biochemistry of plants. It causes osmotic disturbance, nutritional imbalance, malfunction of photosynthetic machinery, and oxidative stress. Rapid urbanization and industrialization are polluting the arable lands with heavy metals which not only affects crop productivity but also interferes with human health. In the modern era, heavy metals, like lead, cadmium, chromium, mercury, and copper are main environmental hazards, especially in regions of higher anthropogenic activity. Contamination of agricultural soils with heavy metals is a serious concern owing to its deleterious effects on agricultural productivity, phytotoxicity, food safety, and quality of the environment with ultimate impact on human health. All these abiotic stresses negatively affect several growth and developmental processes of plants which reduce the productivity of agronomic crop and also deteriorate the quality of produce. To cope with the situation, it is inevitable to understand the adverse effects of these abiotic factors on crop plants. This chapter provides comprehensive information on the impacts of abiotic stresses on crop plants.
The use of costly chemical nitrogen fertilizers for increased food production is a global concern due to their economic and environmental effects. It is the dire need of the day to find out some alternative to the nitrogen fertilizers which is economical and environmentally safe. Biological fixation of atmospheric diatomic nitrogen into a form useable by the plant is a possible alternative to the chemical nitrogen fertilizer which is economically viable, ecologically desirable, and environmentally safe with reduced external inputs. In most of the symbiotic systems, Rhizobium-legume association contributes its major part in providing the N to most of the cropping system, whereas Anabaena and Azolla can be important in reduced conditions such as flooded rice. Despite the importance of nitrogen fixation, there are a number of sociocultural and scientific constraints that limit the adoption of BNF system in agriculture. The major limitation is the hindrance in the management of nutrients in the soil using the BNF as sustainable system. However, if these limitations are handled carefully on scientific basis, then BFN can be a potential source for the management of soil nutrients. Crop residues from nodulated crops also provide nutrients especially nitrogen to the subsequent crops. By adopting the BFN as cropping system, it can cut the heavy use of nitrogen fertilizer which is not only costly but also polluting the environment especially the groundwater. However, optimization of nitrogen fixation can balance the use of fertilizer and thus can help to manage the nutrients for the crops in a sustainable manner. In the present chapter, it is discussed how BNF can be crucial in managing the nutrients.
Soil is threatened by the increase of human population, intensive management, urbanization and degradation. Sustainable Soil Management (SSM) is one of the main key factors both for significant crop production and for environment conservation. Conservation tillage techniques, especially applied together with the permanent maintenance of mulch cover on the soil surface as well as the diversification of cropping system (Conservation Agriculture (CA) system), induce positive changes to soil properties and characteristics. Additional C is sequestered from the atmosphere reducing climate change and increasing net C accumulation in long periods. In term of physical aspects, soil porosity, thanks to increased density of storage pores and elongated transmission pores, increases, saturated and unsaturated hydraulic conductivity improves, more stable aggregates are found, and, as consequence, water holding capacity and water use efficiency ameliorate while soil erosion reduces. The soil pH, CEC, exchangeable cations, and soil principal macronutrients availability, especially at surface layer level, are found to improve as well as soil biota including both invertebrates and microorganisms thanks to an increased densities and diversity.
The intensification of tillage agriculture has been aimed to increase crop yields. However, this has also been causing degradation of agricultural lands and natural resources. In this regard, Conservation Agriculture (CA) is an alternate paradigm, which integrate the conservation into agriculture and make that regenerative, conserving and resilient than the conventional tillage agriculture. CA is, thus, an ecosystem approach to improve and sustain productivity, and increase profits and resource base. In this chapter, some aspects of conservation that are integrated into agriculture when practicing CA are described. The potential of CA in improving productivity, economic, social and environmental benefits to farmers and the society at large have been discussed.
Uncertainties exist about the importance of rhizobia inoculant and starter nitrogen (N) application in dry pea (Pisum sativum L.) production. Three field experiments were conducted to evaluate how rhizobia inoculant and starter N fertilizer affect pea seed yield and protein concentration in a semiarid environment in central Montana. Commercial rhizobia inoculant was mixed with seed prior to planting at the manufacturer’s recommended rate. Starter N fertilizers were applied into the same furrow as seed at 0, 22, 44 and 88 kg ha−1 as urea, slow-release polymer-coated N fertilizer (ESN), and a combination of both. The application of rhizobia inoculant had no or a very small beneficial effect on pea yield in lands with a previous history of peas. In a land without pea history, application of rhizobia increased pea seed yield by 16%. The positive effect of starter N was only pronounced when initial soil N was low (≤ 10 kg ha−1 nitrate-nitrogen), which increased net return by up to US$ 42 ha−1
. In this condition, application of slow-release N outperformed urea. However, application of starter N (especially
with urea) had a negative effect on pea establishment, vigor and seed yield when soil initial N was high (≥ 44 kg ha−1 NO3-N). The results indicate that the rate, placement, and form of the starter N must be optimized to benefit pea yield and protein without detrimental effects on germination and nodulation. Moreover, application of starter N must be guided by the soil nitrate content.
Soil is an extremely complex growth medium, with an enormous biodiversity of fauna and flora, widely differing mineral and organic matter composition, and a complex multi-scaled network of three-dimensional pore space. Soil strength and physical conditions can exert a major constraint to root growth. Hard soils with massive structures restrict the accessibility of nutrients and water to plants. In many laboratory and glasshouse experiments, and in much of horticulture, plants are now cultured using agar, nutrient solution, or artificial composts, an environment very different to the natural one. We must understand the most important factors and stresses that limit root growth in soil, so that results gained in vitro can be related to agricultural and natural ecosystems. Laboratory studies should concentrate on the most important, rather than the technically most convenient, problems. These problems must also be considered in appropriate combination — for example, in many soils, water stress will be accompanied by a large increase in soil strength and hence mechanical impedance to root growth. In this chapter the impact of soil structure, composition and strength on root ecology and resource acquisition by plants is considered.
Introduction Sources of nitrogen and phosphorus to soil-plant systems Chemical and biological processes of nutrient cycling, transformations and bioavailability Processes of nitrogen and phosphorus losses from soils Nitrogen and phosphorus use in agricultural systems Future soil nutrient cycles and environmental change References
The ability of soybean to nodulate with a wide range of indigenous bradyrhizobia has been used in a breeding programme since 1997 in Nigeria. As far as is known, these indigenous bradyrhizobia strains have not been tested for compatibility and effectiveness with recent selections from a breeding programme which has proceeded without input from soil microbiologists for the last 20 yr. Twenty bradyrhizobia strains isolated from soyabean and cowpea grown in Ibadan and Zaria soils in Nigeria were examined in a pot experiment for symbiotic effectiveness on two promiscuous soyabean breeding lines (TGX 1660-19F and TGX 1456-2E) and a cowpea cultivar (IT 849-92). Two bradyrhizobial isolates (R25B and IRj 2180A) had an average symbiotic effectiveness (SE) of 2.36-fold and 1.62-fold of the uninoculated control when inoculated on 1456-2E and 1660-19F, respectively. These strains, however, were less effective on cowpea having a SE of 1.20-fold. Cowpea bradyrhizobia inoculated on promiscuous soyabeans produced less than 77 nodules plant−1 compared to an average of 120 by the two best bradyrhizobia strains from soyabean. The best isolates (R25B, IRj 2180A and their mixture) and one cowpea bradyrhizobia (IRc 461) were further tested on these lines under field conditions at three sites in different agroecological zones in moist savanna (Fashola, Mokwa and Zaria) in Nigeria. Both soyabean lines nodulated with the local rhizobia, but the degree of effectiveness depended on the plant genotype and field sites. Soyabean line 1456-2E showed improved growth and yield in response to N fertilizer application indicating that in this line N2 fixation induced by the indigenous bradyrhizobial community supplied less than optimal amounts of N. The mixture of bradyrhizobial isolates R25B and IRj 2180A increased grain yield of 1456-2E by 30 and 25% at Zaria and Mokwa but failed to do so at Fashola. Grain yield of 1660-19F was not affected by bradyrhizobial inoculation and N fertilizer at any of the three sites. Thus, the need for bradyrhizobia inoculation will be determined by the degree of promiscuity of soybean lines and the effectiveness of the community of indigenous bradyrhizobia present in the site.
Bromocresol green, new coccine, and p-nitrophenol are used as a mixed indicator in Kjeldahl nitrogen titration.
In a green-house experiment, five cultivars of Pisum sativum L. grown on soils from 10 different locations in Tunisia, showed significant differences in nodulation, shoot dry matter (shDM) yield and shoot nitrogen content (shNC). The effect of soil on biological nitrogen fixation, as evidenced by the number and weight of nodules, was mainly attributable to the available phosphorus content. Cate-Nelson ANOVA analysis established a critical value of soil test phosphorus (STP) of 20 mg P kg–1 soil for nodule weight and number for the majority of cultivars. Within cultivars, nodulation varied with maturation period and was correlated with shoot NC. Thus, the overall interaction of soil-P content and cultivar-maturation period were correlated positively with nodulation and to symbiotic effectiveness of strains of Rhizobium leguminosarum bv. viceae indigenous to these soils. Based on an antibiotic susceptibility test and main variable factor analysis of the data obtained, 70 isolates of Rhizobia that nodulate pea, obtained from soils from agricultural sites throughout Tunisia, were identified as belonging to 18 distinct strains. These classes were identified on the basis of symbiotic efficiency parameters (shoot DM yield and shoot NC) as: ineffective (33 isolates), moderately effective (27 isolates), and efficient strains (10 isolates). This study shows that the Mateur site, an agricultural area for millennia in the northern region of Tunisia, harbors rhizobial strains that are highly efficient in fixing N2 with peas. These results also indicate the importance of strain-cultivar interrelationships and specificity.
Pea (Pisum sativum L.) plants inoculated with Rhizobium leguminosarum bv. viciae effective strain 248 were irrigated with nitrogen-free medium supplemented with 0, 25, 50 or 75mM NaCl. The inhibitory
effect of salinity on the growth of pea plants treated with 25mM NaCl occurred 6weeks post inoculation. In case of 75mM
NaCl treatment, the same effect was observed 2weeks post inoculation. In contrast to investigations described in the literature
our results clearly indicated that 25mM NaCl stimulated nodule formation, however, in contrast to control nodules (the medium
without NaCl), the nodules were considerably smaller. Remaining variants of salt treatment reduced plant growth, nodulation,
and total nodule volume calculated per plant. Microscopic observations showed that salinity: (1) caused the loss of turgor
of the nodule peripheral cells, (2) changed nodule zonation, (3) stimulated infection thread enlargement and expansion, (4)
caused disturbances in bacterial release from the infection threads, and (5) induced synthesis of electron dense material
(EDM) and its deposition in vacuoles. It was also found that cisternae of RER were involved in the formation of special cytoplasmic
compartments responsible for synthesis of EDM. Autofluorescence study revealed that salinity increased accumulation of phenolics
in pea nodules, as well.
This handbook is a reference guide for selecting and carrying out numerous methods of soil analysis. It is written in accordance with analytical standards and quality control approaches. It covers a large body of technical information including protocols, tables, formulae, spectrum models, chromatograms and additional analytical diagrams. The approaches are diverse, from the simplest tests to the most sophisticated determination methods in the physical chemistry of mineralogical and organic structures, available and total elements, soil exchange complex, pesticides and contaminants, trace elements and isotopes.As a basic reference, it will be particularly useful to scientists, engineers, technicians, professors and students, in the areas of soil science, agronomy, earth and environmental sciences. It is also relevant to those in related fields such as analytical chemistry, geology, hydrology, ecology, climatology, civil engineering and industrial activities associated with soil.
For optimum production, the use of commercial rhizobial inoculant on pea (Pisum sativum L.) at seeding is necessary in the absence of compatible rhizobial strains or when rhizobial soil populations are low or symbiotically ineffective. Multiple site experiments were conducted to characterize the abundance and effectiveness of resident populations of Rhizobium leguminosarum bv. viciae (Rlv) in eastern Canadian prairie soils. A survey of 20 sites across a broad geographical range of southern Manitoba was carried out in 1998 and was followed by more intensive study of five of the sites in 1999 and 2000. Appreciable nodulation of uninoculated pea was observed at all sites which had previously grown inoculated pea. However, uninoculated pea grown at two sites, which had not previously grown pea, had negligible nodulation. Likewise, wild Lathyrus sp. and Vicia sp. plants collected from uncultivated areas adjacent to agricultural sites were poorly nodulated. In the more intensively studied sites, there was a tendency towards higher nodulation in pea plants receiving commercial inoculant containing Rlv strain PBC108 across all site-years (e.g., 4.7% in nodulation and 22% in nodule mass), but the effect was significant at only 2 of 10 site-years. Despite a relatively high range of soil pH (6–8), regression analysis indicated that decreasing soil pH resulted in lower nodulation rates. Likewise, electrical conductivity (EC) was correlated to nodulation levels, however the effect of EC was likely more indicative of the influence of soil texture and organic matter than salinity. As with nodulation, commercial inoculation tended to increase above-ground dry matter (DM) and fixed-N (estimated by the difference method) at the early pod-filling stage, but again the effects were significant at only 2 of 10 site-years. Specifically, above-ground DM and fixed-N levels were up to 29 and 51% greater, respectively, in inoculated compared to non-inoculated treatments at these sites. Addition of N-fertilizer at a rate of 100 kg N ha−1 decreased nodulation at almost all site-years (by as much as 70% at one site), but rarely resulted in increases in above-ground DM compared to inoculated plots. The study indicates for the first time that populations of infective, and generally effective strains of Rlv occur broadly in agricultural soils across the eastern Canadian prairie, but that there is a tendency for increased symbiotic efficiency with the use of commercial inoculant.
Pea seed protein content (SPC) and seed dry weight (SDW) are both influenced by genetic and environmental factors. To assess the variations of these within-plant traits between seeds, six genotypes were field tested. The sequential seed development at nodes along the main stem was determined. Nitrogen fixation was measured by the acetylene reduction assay (ARA). At maturity, protein content and dry weight were measured according to seed position on the plant. Individual protein content was determined by near-infrared transmission spectroscopy. The results show a significant difference in protein content between nodes of the genotypes Solara, L765 and L833. Protein content tended to decrease from the bottom to the top of the plant for these genotypes. The difference in protein content between the lowest and the uppermost node was about 26 g kg–1 for Solara, 40 g kg–1 for L765 and 49 g kg–1 for L833. There were also significant differences in dry weight between plant nodes for all genotypes, except Finale. In addition, the range of difference in dry weight between plant nodes was higher than that for protein content. Further, to determine the influence of morphological position on individual protein content and dry weight, multiple linear regression was established on node position, pod position on the node, and seed position within pods. The results showed that protein content and dry weight were not influenced either by within-pod seed position or pod position on the raceme. Moreover, protein content and dry weight were mainly influenced by node position on the main stem. However, for protein content, the effect of node position varied with genotype, indicating a genetic variability for this character. This genetic variability could be attributed to the difference between genotypes in the ability to maintain nitrogen fixation during the onset of seed filling. For dry weight, the decrease in seed weight for upper nodes of the plant also varied with genotype in relation to the duration of seed filling and the seed growth rate.
Agronomical Behaviour of a Pea Collection (Pisum sativum L.). This experience was achieved under greenhouse conditions. Twelve genotypes of pea were used (Asgrow, Jumbo, Lincoln, Merveille de Kelvedon, Purser, Rajai Torpe, Snajor Kosep, Korai,Wando, Rondo, local genotype, Major Kosep Korai and Surgevil). They were cultivated on peat during 5.5 months (from October to April). Some agronomical parameters were studied: resistance to diseases, (Powdery-mildew, mildew, top yellow virus, anthracnose, browning), fresh matter, number of branches/plant, number of flowers/plant, number of pods/ plant and the yield of grains /plant. Results showed that only the genotype Purser is resistant to all diseases and Surgevil is sensitive only to the Top Yellow virus. The local genotype is sensitive to three frequent diseases (Powdery-mildew, mildew and Anthracnose). With regard to vegetative growth, the highest yield of fresh matter do not contribute towards a high fertility rate. In fact, only the genotypes having a weak yield of fresh matter (Snajor Kosep Korai, Asgrow, Major Kosep Korai, Rajai Torpe and Purser) have the most important rate of fertility (> 30%). Within this group, the most important yield (> 9 g/plant) is a result of high: number of pods/plant (7.5 to 21.6) and of grains/pod (2.8 to 4.92). Finally, genotype Purser should be retained for farmers and programs of genetic amelioration for its resistance to diseases and agronomical performances.
This study was designed to evaluate N<SUB>2</SUB>-fixation and N balance of improved cowpea and soybean genotypes in the NGS of Nigeria. Field experiments were conducted in 2003 and 2004 to assess nodulation, N<SUB>2</SUB> fixation and N contribution of two cowpea (IT96D-274 and SAMPEA-2) and soybean (SAMSOY-2 and TGx 1448-2E) on a leached ferruginous tropical soil (Haplustalf). The legume genotypes and a reference maize crop (Oba Super 2) were planted in randomized complete block design with three replications. The N difference method was used in estimating symbiotic N<SUB>2</SUB> fixation while the N contribution was estimated by the difference between N fixed and N exported in the grain during harvest. Although nodule number did not differ significantly among genotypes, the weight was significantly higher in soybean than cowpea. Significant difference in N<SUB>2</SUB> fixation was only observed between cowpea genotypes and it was attributed to the differences in maturity period. TGx 1448-2E derived on average 49.8 kg N ha<SUP>-1</SUP> or 37% of plant total N from fixation compared to IT96D-724 with 15.8 kg N ha<SUP>-1</SUP> or 19%. In both years, N balance ranged from -30 to 9 kg N ha<SUP>-1</SUP> depending on the genotype. With the exception of SAMPEA-7 in 2003, all genotypes led to a net negative contribution to soil N and a positive N balance was only obtained when the nitrogen harvest index was less than the proportion of Ndfa. The results show that reasonable maize yield may not be obtained following these grain legumes without supplementary N added to the soil.
Sinorhizobium meliloti is a nitrogen-fixing alpha-proteobacterium present in soil and symbiotically associated with root nodules of leguminous plants. To date, estimation of bacterial titres in soil is achieved by most-probable-number assays based on the number of nodules on the roots of test plants. Here, we report the development of two real-time PCR (qPCR) assays to detect the presence of S. meliloti in soil and plant tissues by targeting, in a species-specific fashion, the chromosomal gene rpoE1 and the pSymA gene nodC.
rpoE1 and nodC primer pairs were tested on DNA extracted from soil samples unspiked and spiked with known titres of S. meliloti and from plant root samples nodulated with S. meliloti. Results obtained were well in agreement with viable titres of S. meliloti cells estimated in the same samples.
The developed qPCR assays appear to be enough sensitive, precise and species-specific to be used as a complementary tool for S. meliloti titre estimation.
These two novel markers offer the possibility of quick and reliable estimation of S. meliloti titres in soil and plant roots contributing new tools to explore S. meliloti biology and ecology including viable but nonculturable fraction.
Wild legumes (herb or tree) are widely distributed in arid regions and actively contribute to soil fertility in these environments. The N2-fixing activity and tolerance to drastic conditions may be higher in wild legumes than in crop legumes. The wild legumes in arid zones harbor diverse and promiscuous rhizobia in their root-nodules. Specificity existed only in few rhizobia from wild legumes, however, the majority of them are with wide host range. Based on phenotypic characteristics and molecular techniques (protein profiles, polysaccharides, plasmids, DNA-DNA hybridization, 16SrRNA, etc.), the root-nodule bacteria that was isolated from wild legumes had been classified into four genera (Rhizobium, Bradyrhizobium, Mesorhizobium and Sinorhizobium). The rhizobia of wild legumes in arid zones, exhibit higher tolerance to the prevailing adverse conditions, e.g. salt stress, elevated temperatures and desiccation. These rhizobia may be used to inoculate wild, as well as, crop legumes, cultivated in reclaimed desert lands. Recent reports indicated that the wild-legume rhizobia formed successful symbioses with some grain legumes. Moreover, intercropping of some N2-fixing tree legumes (e.g. Lablab, Leucaena, Sesbania, etc.) to pasture grasses improved biomass yield and herb quality. In recent years, the rhizobia of wild legumes turn the attention of biotechnologists. These bacteria may have specific traits that can be transferred to other rhizobia through genetic engineering tools or used to produce industrially important compounds. Therefore, these bacteria are very important from both economic and environmental points of view.
Know Your Soils -Part 1 Introduction to Soils
- N M Baxter
- J R Williamson
Baxter, N.M., Williamson, J.R., 2001. In: Printers, Mulqueen (Ed.), Know Your Soils -Part
1 Introduction to Soils. Bendigo, Victoria.
PRIMER V6: User Manual/Tutorial. PRIMER-E (Plymouth Routines in Multivariate Ecological Research
- K R Clarke
- R N Gorley
Clarke, K.R., Gorley, R.N., 2006. PRIMER V6: User Manual/Tutorial. PRIMER-E
(Plymouth Routines in Multivariate Ecological Research) (Plymouth).
Know and preserve biodiversity
- Cluzeau
Cluzeau, D., 2017. Know and preserve biodiversity. In: Pauthier, D. (Ed.), Maps and Soil
Data. Tools Serving Territories. Educagri, Dijon, pp. 142-155.
Importance of Bacterial Genetic Variability on the Functioning of the Rhizobium Leguminosarum Biovar Viciae Symbiosis with Peas
- Geraldine Depret
Depret, Geraldine, 2008. Importance of Bacterial Genetic Variability on the Functioning
of the Rhizobium Leguminosarum Biovar Viciae Symbiosis with Peas (Pisum sativum
L.). Bourgogne University, Dijon.