QTL Mapping of Aluminum Tolerance in Tetraploid Alfalfa

Aluminum (Al) toxicity in acid soils is one of the factors limiting crop production. Alfalfa (Medicago sativa L.) is one of the most important forage legumes worldwide and is susceptible to Al toxicity. Al tolerance in alfalfa was identified in a diploid Medicago sativa subs. caerulea accession (Sledge et al., 2002) and has been successfully integrated at the tetraploid level in the Al-tolerant genotype Altet-4. The goals of this study are to identify and confirm quantitative trait loci (QTL) for Al-tolerance in tetraploid alfalfa. Two populations of at least 190 individuals each were developed from crosses between Altet-4 (Al-tolerant) and the AI-susceptible genotypes 95-608 derived from CUF-101, and NECS141, a semi-dormant breeding line developed in Iowa. The parental lines and the progeny from the mapping populations were screened using a callus bioassay and a whole plant assay. Genetic linkage maps constructed using EST-SSR markers (Sledge et al., 2005) were developed and used to identify QTL associated with Al tolerance. Comparison of QTL identified using different screening methods will be discussed. The long-term goal of this research is to use molecular markers associated with the Al-tolerance trait to accelerate the development of alfalfa cultivars with improved productivity in acidic and Al-toxic soils.