Assessment of genetic diversity among nondormant and semidormant alfalfa populations using sequence-related amplified polymorphisms

Synthetic populations of alfalfa (Medicago sativa L.) consist of genetically heterogeneous mixtures of plants, which may complicate use of molecular markers for examining genetic relationships among populations. Molecular marker techniques combined with bulked DNA from multiple plants provides perhaps the best combination of accuracy and high throughput for characterization and differentiation of alfalfa populations. Using 20-plant bulked DNA templates we assessed how sequence-related amplified polymorphisms (SRAPs) would estimate genetic similarity among 29 nondormant and semidormant alfalfa populations representing diverse genetic backgrounds and the nine historically recognized U.S. germplasm sources. Cluster analysis based on estimates of genetic similarity showed separation of populations in fall dormancy classes 6 to 8 (semidormant) from fall dormancy classes 9 to 11 (nondormant) and in many examples, DNA bulks of the same population clustered together. A single SRAP marker was identified that was present only in bulks of fall dormancy classes 6 and 7, and another marker was identified that was detected only in bulks of fall dormancy class 8. This study demonstrates that the amplification of SRAP markers from DNA extracted from bulked plant samples is an efficient method for estimating genetic similarity both within and between a large numbers of populations. The SRAPs may also be useful for indirectly classifying relative fall dormancies of uncharacterized populations.