Identification of Aluminum Tolerance Quantitative Trait Loci in Tetraploid Alfalfa
Aluminum (Al) toxicity in acid soils is one of the factors limiting crop production. Alfalfa (Medicago sativa L.) is the most important forage legume worldwide and is susceptible to Al toxicity. Our objective was to identify genomic regions associated with Al tolerance in tetraploid alfalfa. A segregating population obtained from a cross between Altet-4 (Al-tolerant genotype) and NECS-141 (Al-sensitive genotype) was evaluated for Al tolerance using a callus bioassay and a whole plant assay in media and genotyped using molecular markers. Phenotyping results for both callus and root growth assays exhibited a normal distribution and patterns of transgressive segregation. The linkage maps covered 761 cM for Altet-4 and 721 cM for NECS-141. Markers associated with Al tolerance from both assays were detected using single-factor analysis. Quantitative trait loci (QTL) for Al tolerance were identified on linkage groups (LGs) 1, 4, and 7 using interval mapping, and these QTL explained 20.8, 15.2, and 21.7% of the variation, respectively. A second population was used to evaluate the identified Al tolerance QTL in a different genetic background. Although mechanisms of Al tolerance in tetraploid alfalfa are quantitative, the identification of relevant genomic regions and candidate genes involved in abiotic stress responses can facilitate the selection of desirable alleles to accelerate the development of alfalfa cultivars that can be productive in acid and Al-toxic soils.
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