Quantitative trait loci and candidate gene mapping of aluminum tolerance in diploid alfalfa

Abstract

Aluminum (Al) toxicity in acid soils is a major limitation to the production of alfalfa (Medicago sativa subsp. sativa L.) in the USA. Developing Al-tolerant alfalfa cultivars is one approach to overcome this constraint. Accessions of wild diploid alfalfa (M. sativa subsp. coerulea) have been found to be a source of useful genes for Al tolerance. Previously, two genomic regions associated with Al tolerance were identiWed in this diploid species using restriction fragment length polymorphism (RFLP) markers and single marker analysis. This study was conducted to identify additional Al-tolerance quantitative trait loci (QTLs); to identify simple sequence repeat (SSR) markers that Xank the previously identiWed QTLs; to map candidate genes associated with Al tolerance from other plant species; and to test for co-localization with mapped QTLs. A genetic linkage map was constructed using EST-SSR markers in a population of 130 BC 1 F 1 plants derived from the cross between Al-sensitive and Altolerant genotypes. Three putative QTLs on linkage groups LG I, LG II and LG III, explaining 38, 16 and 27% of the phenotypic variation, respectively, were identiWed. Six candidate gene markers designed from Medicago truncatula ESTs that showed homology to known Al-tolerance genes identiWed in other plant species were placed on the QTL map. A marker designed from a candidate gene involved in malic acid release mapped near a marginally signiWcant QTL (LOD 2.83) on LG I. The SSR markers Xanking these QTLs will be useful for transferring them to cultivated alfalfa via marker-assisted selection and for pyramiding Al tolerance QTLs.

Quantitative Trait Loci and Crop Performance under Abiotic Stress: Where Do We Stand?: Table I.

“…Liming and use of tolerant crop varieties can be used to treat soil acidity . Major loci and QTLs controlling Al tolerance have been identified in alfalfa (Medicago sativa; Narasimhamoorthy et al, 2007), soybean (Bianchi-Hall et al, 2000), rice (Xue et al, 2007), sorghum , maize (Ninamango-Cárdenas et al, 2003), barley , wheat (Raman et al, 2005), oat (Avena sativa; Wight et al, 2006), and rye (Secale cereale; Matos et al, 2005). Comparative mapping has indicated possible homologies between Al tolerance loci in different cereal species .…”

Applied Genetics and Genomics in Alfalfa Breeding

“…Currently, simple sequence repeat (SSR) markers are widely used for QTL analysis in alfalfa, most of which were derived from Medicago truncatula [52]. The SSR markers have facilitated genetic studies of alfalfa, including genetic map construction [53][54][55], comparative mapping [53,56], population structure analysis [11] and QTL identification [37,57]. However, the number of SSR markers is insufficient for the needs of fine mapping and genome-wide association studies.…”

“…Major QTL related to yield and morphological traits [37,38], fall dormancy and winter-hardiness [69,70], persistence [71], viability [53], self-fertility [72], resistance to Stagonospora melioti [68], resistance to C. trifolii [73], aluminum tolerance [57,74] and water use efficiency [75] have been mapped in alfalfa, primarily in tetraploid populations (Table 1). Several factors potentially limit the precision and power of mapping in tetraploid alfalfa.…”

Breeding lucerne for persistence

“…In several assays it grew as well in tissue culture with Al as in the absence of Al (Sledge et al 2002). QTL mapping identified several genomic regions associated with Al tolerance in this diploid genotype based on callus assays (Sledge et al 2002;Narasimhamoorthy et al 2007). This genotype therefore possessed a unique source of Al tolerance genes, which had promise for being tagged and transferred via molecular markers into cultivated, tetraploid genotypes and finally becoming parental material to develop tolerant cultivars.…”