SRAP polymorphisms associated with superior freezing tolerance in alfalfa (Medicago sativa spp. sativa).

Sequence-related amplified polymorphism (SRAP) analysis was used to uncover genetic polymorphisms among alfalfa populations recurrently selected for superior tolerance to freezing (TF populations). Bulk DNA samples (45 plants/bulk) from each of the cultivar Apica (ATF0), and populations ATF2, ATF4, ATF5, and ATF6 were evaluated with 42 different SRAP primer pairs. Several polymorphisms that progressively intensified or decreased with the number of recurrent cycles were identified. Four positive polymorphisms (F10-R14, Me4-R8, F10-R8 and F11-R9) that, respectively, yielded 540-, 359-, 213-, and 180-bp fragments were selected for further analysis. SRAP amplifications with genotypes within ATF populations confirmed that the polymorphisms identified with bulk DNA samples were reflecting changes in the frequency of their occurrence in response to selection. In addition, the number of genotypes cumulating multiple polymorphisms markedly increased in response to recurrent selection. Independent segregation of the four SRAP polymorphisms suggests location at unlinked loci. Homology search gave matches with BAC clones from syntenic Medicago truncatula for the four SRAP fragments. Analysis of the relationship with low temperature tolerance showed that multiple SRAP polymorphisms are more frequent in genotypes that maintain superior regrowth after freezing. These results show that SRAP analysis of bulk DNA samples from recurrent selections is an effective approach for the identification of genetic polymorphisms associated with quantitative traits in allogamous species. These polymorphisms could be useful tools for indirect selection of freezing tolerance in alfalfa.