EST-SSRs for Genetic Mapping in Alfalfa

Several genetic maps of alfalfa have been published, both at the diploid (Medicago sativa subsp. coerulea) and tetraploid (Medicago sativa L.) levels. These maps have been constructed primarily with RFLP and RAPD markers, and have not been integrated into a single, reference map. The development of reliable, publicly available PCR-based markers would provide a basis for unifying the variously available alfalfa genetic maps. The goal of the present research is to construct a molecular map of tetraploid alfalfa using EST-derived SSR markers. Two alfalfa backcross populations have been constructed from a cross between a water-use efficient, M. falcata genotype and a low water-use efficient M. sativa genotype of Chilean origin. These populations are also segregating for yield, fall dormancy, and winter hardiness. We have screened 333 primer pairs amplifying M. truncatula EST-SSRs, approximately 50% of which are polymorphic between the Chilean and M. falcata parents. We have currently identified a total of 216 single-dose alleles from 125 polymorphic EST-SSRs, and are constructing an EST-SSR map that will be used for identifying QTLs for drought tolerance in autotetraploid alfalfa.