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Partial genetic map of the apple rootstock 'Malling 9' ('M.9') linkage group 5 (LG 5) around the dwarfing locus. LG 5 of 'M.9' aligned with 'Fiesta' LG 5 from Silfverberg-Dilworth et al. (2006). Microsatellite markers mapped in 'M.9' are highlighted in bold text, with dashed lines illustrating microsatellite markers in common with 'Fiesta' LG 5. The dwarfing locus is identified as Dw1 in bold text. A gel showing the PCR products from the SCAR marker NZscAE16_1700 of 18 individuals from the 'M.9' · 'Robusta 5' ('R5') population, phenotyped as dwarfed (DW) or vigorous (V), as well as from mapping population parents 'M.9' and 'R5' is shown, with a 100-bp ladder (Invitrogen, Carlsbad, CA).
Source publication
Little is known of the precise physiological or genetic basis of the phenomenon of rootstock-induced dwarfing in apple (Malus x domestica Borkh.). Phenotypic assessment and genetic marker analysis of a segregating population of apple rootstocks derived from a cross between the dwarfing rootstock 'Malling 9' ('M.9') and the vigorous rootstock 'Robus...
Contexts in source publication
Context 1
... identified that the locus detected by the marker NZraAJ13 had an excess of 'M.9' alleles (c 2 = 11.1, P = 0.0008). As this marker locus also appeared to result in 24 double crossovers when it was mapped in proximity to the other loci, it was discarded from the mapping exercise. Two of the RAPD markers were converted to SCAR markers (Table 1 and Fig. 3). The segregation of these markers was scored and incorporated in the linkage analysis in place of the original RAPD scores for NZraAI2_1200 and ...
Context 2
... with the dwarfing phenotype had been previously shown to be located on linkage group 5 (LG 5) of the apple genetic map ( Liebhard et al., 2002). The conservation of marker order and distances between the partial 'M.9' map and the 'Fiesta' · 'Discovery' reference map strongly indicated that the dwarfing locus was located at the top of LG 5 (Fig. ...
Context 3
... nature that favors their transferability between different cultivars to identify loci in individuals from the segregating 'M.9' · 'R5' population, which in turn allowed the identification of the linkage group containing the Dw1 locus as LG 5. The conservation of marker order between the 'Fiesta' · 'Discovery' reference map and the map of 'M.9' (Fig. 3) illustrates the robustness of this approach and the usefulness of a consensus framework ...
Similar publications
Current control strategies for the major apple disease European canker (EC) are laborious and expensive, and often do not prevent progression of the disease, which can lead to loss of trees and therefore production. Hence, the development of resistant cultivars is a significant goal for breeders supporting growers in maritime climates conducive to...
Citations
... production has benefited from widespread use of dwarfing Malus rootstocks, the closely related pear (European; Pyrus communis L.) lacks comparable dwarfing Pyrus rootstocks [4] . In most U.S. pear orchards, threedimensional trees on semi-to-vigorous rootstocks are planted at low densities of 500 to 1,800 trees per hectare [5] . Though quince (Cydonia oblonga Mill.) is widely used as a size-controlling rootstock in global pear production (particularly in Europe), concerns of cold-hardiness and graft incompatibility have precluded its adoption in the U.S. ...
... spinosa × P. elaeagrifolia) were used due to their phenotypic segregation for vigor. 'OH×F 333' is a semi-dwarfing rootstock [5] that came from the 'Old Home' by 'Farmingdale' series that was originally developed to combine fire blight resistance and desirable horticultural traits [13] . Recent genotypic data elucidated the correct parentage of 'OH×F 333' as 'Old Home' by 'Bartlett' [14] . ...
US pear production is constrained by the lack of dwarfing and precocious rootstocks that revolutionized other fruit crops, such as apple. While quince is used as a rootstock in global pear production, concerns about potential graft incompatibility and lack of cold hardiness limit its adoption in the US. This work was aimed at identifying genetic determinants of dwarfing in Pyrus backgrounds to inform future breeding for dwarfing Pyrus rootstocks. In 2018, 145 rootstock seedlings of two reciprocal crosses were budded with a standard scion variety. Rootstock seedlings were also genotyped with the 70 K Pyrus SNP array. Based on two-year orchard architectural phenotypes, quantitative trait loci (QTLs) were consistently mapped on both chromosomes 5 and 15 for dwarfing traits, namely scion trunk cross-sectional area (TCA), total scion annual growth, and central leader annual growth. QTLs for rootstock TCA were also detected on both chromosomes 5 and 15; however, the chromosome 15 QTL did not co-localize with the scion trait locus. Each dwarfing haplotype accounted for 30% to 50% reduction in vigor (p < 0.05). Combined haplotype analysis showed that one dwarfing locus was sufficient to significantly reduce vigor. Presence of two dwarfing haplotypes further reduced vigor by a total of 50% to 70% (p < 0.05), but their combinatory effects were not purely additive due to epistasis. Discovery of these novel dwarfing loci (named P×Dwg1 and P×Dwg2) in Pyrus facilitates future DNA test development to enable informed parental and seedling selection for dwarfing potential.
... However, many of these architectural forms are not conducive to planned agriculture and orchard management, possessing innate architectures that are too vigorous or crown architectures that inhibit production (Lauri et al., 1997). This problem can be addressed by several approaches, either by direct human intervention in the form of coordinated pruning and shaping (tree training systems; Lauri, 2002), or by reducing/controlling the innate architectures common in modern cultivars (dwarfing rootstocks; Pilcher et al., 2008;Reighard et al., 2011). ...
Tree training systems for temperate fruit have been developed throughout history by pomologists to improve light interception, fruit yield, and fruit quality. These training systems direct crown and branch growth to specific configurations. Quantifying crown architecture could aid the selection of trees that require less pruning or that naturally excel in specific growing/training system conditions. Regarding peaches [Prunus persica (L.) Batsch], access tools such as branching indices have been developed to characterize tree‐crown architecture. However, the required branching data (BD) to develop these indices are difficult to collect. Traditionally, BD have been collected manually, but this process is tedious, time‐consuming, and prone to human error. These barriers can be circumnavigated by utilizing terrestrial laser scanning (TLS) to obtain a digital twin of the real tree. TLS generates three‐dimensional (3D) point clouds of the tree crown, wherein every point contains 3D coordinates (x, y, z). To facilitate the use of these tools for peach, we selected 16 young peach trees scanned in 2021 and 2022. These 16 trees were then modeled and quantified using the open‐source software TreeQSM. As a result, “in silico” branching and biometric data for the young peach trees were calculated to demonstrate the capabilities of TLS phenotyping of peach tree‐crown architecture. The comparison and analysis of field measurements (in situ) and in silico BD, biometric data, and quantitative structural model branch uncertainty data were utilized to determine the reconstructive model's reliability as a source substitute for field measurements. Mean average deviation when comparing young tree (YT) height was approx. 5.93%, with crown volume was approx. 13.26% across both 2021 and 2022. All point clouds of the YTs in 2022 showed residuals lower than 12 mm to cylinders fitted to all branches, and mean surface coverage greater than 40% for both the trunk and primary branching orders.
... The M9 is a dwarfing rootstock that belongs to the British M series, and the canopy of the scion varieties grafted on them are ca. 50% smaller compared to other standard rootstocks [4]. The SH series rootstocks were selected and bred after 16 years of research (1978)(1979)(1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993) by crossing Guoguang × Henan Begonia by the Fruit Tree Research Institute of the Shanxi Academy of Agricultural Sciences in China. ...
In apple cultivation, dwarf rootstocks are chosen for dense planting and intensive cultivation, which is beneficial to production management. Dwarf rootstocks are widely used in apple production in China. However, the dwarfing mechanisms of dwarf interstock are still unclear. Here, M9 and SH40 were selected as the dwarf interstocks for potted Fuji apples. The key transcription factor MdWRKY24 was screened via transcriptional sequencing. The open reading frame sequence of the MdWRKY24 gene was 657 bp in length, encoded 218 amino acids, and was located on the cell membrane. The MdWRKY24-overexpressing Arabidopsis line showed a dwarf phenotype and delayed flowering. The DELLA protein RGA-like (RGL) gene is a repressor of the gibberellin signaling pathway. Yeast two-hybrid analysis revealed that MdWRKY24 could interact with MdRGL1/2/3. The results indicated that MdWRKY24 might affect plant dwarfing through the synergistic effect of MdRGL1/2/3. The MdWRKY24-MdRGL may be an important pathway underlying the gibberellin-mediated regulation of apple dwarfing.
... Recent studies have reported mapped locus responsible for controlling dwarfing in apple rootstocks. DW1 was the first locus identified in most of the dwarfing and semidwarfing rootstocks (Pilcher et al., 2008). A second locus, known as DW2, having similar effect on vigor, was later characterized (Fazio et al., 2014). ...
... Quantitative trait loci analysis has revealed that the dwarfing phenotype is controlled by three loci. However, the genes behind those loci remain unknown [45,70,71]. Fine mapping may reveal this information in the future. ...
Above-ground plant architecture is dictated to a large extent by the fates and growth rates of aerial plant meristems. Shoot apical meristem gives rise to the fundamental plant form by generating new leaves. However, the fates of axillary meristems located in leaf axils have a great influence on plant architecture and affect the harvest index, yield potential and cultural practices. Improving plant architecture by breeding facilitates denser plantations, better resource use efficiency and even mechanical harvesting. Knowledge of the genetic mechanisms regulating plant architecture is needed for precision breeding, especially for determining feasible breeding targets. Fortunately, research in many crop species has demonstrated that a relatively small number of genes has a large effect on axillary meristem fates. In this review, we select a number of important horticultural and agricultural plant species as examples of how changes in plant architecture affect the cultivation practices of the species. We focus specifically on the determination of the axillary meristem fate and review how plant architecture may change even drastically because of altered axillary meristem fate. We also explain what is known about the genetic and environmental control of plant architecture in these species, and how further changes in plant architectural traits could benefit the horticultural sector.
... Gardiner et al. (1994) presented the first evidence on how 'M9' and its clonal relatives might induce dwarfing on grafted varieties by using bulked segregant analysis data from a cross between 'M9' and 'Robusta 5' (R5). Subsequent studies on this population identified a major QTL Dwarfing 1 (Dw1), on the top of chromosome 5 of apple that was inducing dwarfing in 'M9' (Pilcher et al., 2008). ...
... Two quantitative trait loci (QTLs), Dw1 and Dwarfing 2 (Dw2), are responsible for rootstockinduced dwarfing in apples (Pilcher et al., 2008;Fazio et al., 2014;Kotoda et al., 2010). Dw1 is located at the top of linkage group/chromosome 5 (LG05) between markers CH03a09 and NZraAM18-700, the Dw2 is on the linkage group/chromosome 11 (LG11) between markers CH02d08 and C13243 (Pilcher et al., 2008;Fazio et al., 2014). ...
... Two quantitative trait loci (QTLs), Dw1 and Dwarfing 2 (Dw2), are responsible for rootstockinduced dwarfing in apples (Pilcher et al., 2008;Fazio et al., 2014;Kotoda et al., 2010). Dw1 is located at the top of linkage group/chromosome 5 (LG05) between markers CH03a09 and NZraAM18-700, the Dw2 is on the linkage group/chromosome 11 (LG11) between markers CH02d08 and C13243 (Pilcher et al., 2008;Fazio et al., 2014). A third QTL (Dw3) has been identified on chromosome 13 in a region previously not related to dwarfing (Harrison et al., 2016). ...
Dwarfing rootstocks in apple have existed for more than a century, and their use revolutionized apple production worldwide. The most notable dwarfing rootstocks, ‘M9’ and ‘M27’, contain three quantitative trait loci (QTLs), Dw1 Dw2 and Dw3, which are the major genetic regulators for rootstock induced dwarfing in apples. Although genetically controlled, the dwarfing physiological mechanisms are still not fully understood, nor is there one main hypothesis. Several rootstock-scion relationships contribute to the dwarfing effect in apple rootstocks. These include modifications in: flowering genes, scion/rootstock vascular tissue anatomy and morphology, carbohydrate allocation, nutrient/water distribution, and hormonal regulation. Cumulatively, these genetic and physiological factors influence the architecture and mechanisms within the tree to facilitate optimal orchard designs and training systems to promote enhanced fruit quality. The history of dwarfing rootstocks in apple and the main hypotheses for the dwarfing mechanism are discussed herein. Future research will require a lot of coordinated effort to fully understand the dwarfing mechanism in apple and seek to control confounding variables in rootstock studies, such as nutrition and the crop load of the tree.
... DNA markers remain the most reliable genetic markers [97] . Apple dwarfing rootstock (M9) is used globally as a genomic asset to breed new rootstocks [98] . Pilcher et al. [99] reported for the first time that the dwarfing ability of the apple rootstock was named Dwarfing 1 (Dw1), which was detected at the position of 2.5-cM between the RAPD DNA marker NZraAM18_700 and simple sequence repeat (SSR) marker CH03a09 at the linkage group 5 of apple rootstock 'Malling 9'. ...
... Gene identification of Dw1 is a major achievement in studying the dwarfing mechanism of apple rootstocks. Furthermore, Foster et al. [98] identified Dw1 and Dw2 dwarfing loci in a cross between apple rootstock 'M9' and non-dwarf 'Robusta5'. Dw2 was identified on LG11, and four small QTLs with little effect on LG6, LG9, LG10, and LG12. ...
Grafting has been commonly practiced for many centuries in the cultivation of horticultural crops. The use of dwarfing rootstocks has enabled a high-density plantation to produce maximum yield. Rootstock regulates scion phenotype, including precocity, fruit size, yield, quality characteristics, and tolerance to various environmental stresses. This review summarizes the existing information on the influence of rootstocks on scion growth and dwarfing mechanisms induced by multiple factors, including hormone signaling, photosynthesis, mineral transport, water relations, anatomical characteristics, and genetic markers. It has been shown that the complex interactions between scion and rootstock can regulate plant development and its structure. This information will provide interesting insights for future research related to rootstock-mediated dwarfing mechanisms and accelerate the breeding progress of dwarfing rootstocks.
... To achieve our goal of developing a crown gall-resistant apple rootstock, marker-assisted selection for these three QTLs could be an efficient approach for pyramiding these loci in a single genotype. The use of SSR markers, together with other relevant markers such as Dw1 (Pilcher et al. 2008;Harrison et al. 2016), woolly apple aphid resistance (Bus et al. 2008) and fire blight resistance (Fahrentrapp et al. 2013), will also improve the efficiency of gene pyramiding. For this objective, cheaper, easy-to-use high-throughput markers including Kompetitive Allele Specific PCR (KASP) should be developed. ...
In apple (Malus spp.), crown gall disease, caused by the bacterial pathogens Rhizobium radiobacter (Ti) and R. rhizogenes (Ti), can be severe. To control the disease, breeding of apple rootstocks that exhibit crown gall resistance is a promising approach. In this study, we used a full-sib F1 population derived from a ‘JM7’ (susceptible) × Sanashi 63 (resistant) cross to identify quantitative trait loci (QTLs) that control resistance to tumour-inducing Rhizobium isolates found in apple production areas in Japan. Three stable QTLs, associated with a wide range of crown gall resistances, were identified in three linkage groups (LGs). QTLs for resistance to isolates Peach CG8331, Nagano 1 and Nagano 2 co-localised at the middle of LG 2 in Sanashi 63, where the crown gall resistance gene Cg (renamed as Rrr1 in this study) was previously identified. Similarly, in ‘JM7’, QTLs were identified on LG 11 for resistance to isolates ARAT-001, ARAT-002 and Kazuno 2, and on LG 15 for resistance to isolate ARAT-001. Fine-mapping of Rrr1 and nucleotide sequencing of a contig obtained from two bacterial artificial chromosome (BAC) clones delimited the Rrr1 gene to a region spanning 217 kb. In silico gene prediction from the region identified four genes encoding the Toll-interleukin-1 receptor/nucleotide-binding site/leucine-rich repeat (TIR-NBS-LRR) class plant resistance genes.
... The predictability of QTL-based markers is likely not transferable to different populations [89,90]. However, the markers for RGA in this study can potentially be used for selecting materials that are genetically related to 'M9' and 'BC', because both 'M9' and 'BC' have been frequently used as parental cultivars in apple rootstock breeding programmes [91][92][93][94]. Apple dwarfing rootstocks usually have a smaller RGA and relatively shallow root architecture [2]. ...
Background
The root growth angle (RGA) typically determines plant rooting depth, which is significant for plant anchorage and abiotic stress tolerance. Several quantitative trait loci (QTLs) for RGA have been identified in crops. However, the underlying mechanisms of the RGA remain poorly understood, especially in apple rootstocks. The objective of this study was to identify QTLs, validate genetic variation networks, and develop molecular markers for the RGA in apple rootstock.
Results
Bulked segregant analysis by sequencing (BSA-seq) identified 25 QTLs for RGA using 1955 hybrids of the apple rootstock cultivars ‘Baleng Crab’ (Malus robusta Rehd., large RGA) and ‘M9’ (M. pumila Mill., small RGA). With RNA sequencing (RNA-seq) and parental resequencing, six major functional genes were identified and constituted two genetic variation networks for the RGA. Two single nucleotide polymorphisms (SNPs) of the MdLAZY1 promoter damaged the binding sites of MdDREB2A and MdHSFB3, while one SNP of MdDREB2A and MdIAA1 affected the interactions of MdDREB2A/MdHSFB3 and MdIAA1/MdLAZY1, respectively. A SNP within the MdNPR5 promoter damaged the interaction between MdNPR5 and MdLBD41, while one SNP of MdLBD41 interrupted the MdLBD41/MdbHLH48 interaction that affected the binding ability of MdLBD41 on the MdNPR5 promoter. Twenty six SNP markers were designed on candidate genes in each QTL interval, and the marker effects varied from 0.22°-26.11°.
Conclusions
Six diagnostic markers, SNP592, G122, b13, Z312, S1272, and S1288, were used to identify two intricate genetic variation networks that control the RGA and may provide new insights into the accuracy of the molecular markers. The QTLs and SNP markers can potentially be used to select deep-rooted apple rootstocks.
... These processes are regulated by phytohormones, whose levels have been proven to be altered by genome duplication (Dudits et al., 2016). Some 2x rootstocks can promote dwarfism in apple trees (Pilcher et al., 2008;Fazio et al., 2014). Polyploid rootstocks have been used commercially to reduce tree size, like citrus 4x somatic hybrid (allotetraploids) and 3x cherry rootstocks (4x P. cerasus L. cv. ...
Synthetic polyploids have been extensively studied for breeding in the last decade. However, the use of such genotypes at the agronomical level is still limited. Polyploidization is known to modify certain plant phenotypes, while leaving most of the fundamental characteristics apparently untouched. For this reason, polyploid breeding can be very useful for improving specific traits of crop varieties, such as quality, yield, or environmental adaptation. Nevertheless, the mechanisms that underlie polyploidy-induced novelty remain poorly understood. Ploidy-induced phenotypes might also include some undesired effects that need to be considered. In the case of grafted or composite crops, benefits can be provided both by the rootstock’s adaptation to the soil conditions and by the scion’s excellent yield and quality. Thus, grafted crops provide an extraordinary opportunity to exploit artificial polyploidy, as the effects can be independently applied and explored at the root and/or scion level, increasing the chances of finding successful combinations. The use of synthetic tetraploid (4x) rootstocks may enhance adaptation to biotic and abiotic stresses in perennial crops such as apple or citrus. However, their use in commercial production is still very limited. Here, we will review the current and prospective use of artificial polyploidy for rootstock and scion improvement and the implications of their combination. The aim is to provide insight into the methods used to generate and select artificial polyploids and their limitations, the effects of polyploidy on crop phenotype (anatomy, function, quality, yield, and adaptation to stresses) and their potential agronomic relevance as scions or rootstocks in the context of climate change.
