Reaction of Medicago Truncatula to Aphanomyces

Aphanomyces euteiches causes root rot disease of alfalfa, and two races of the pathogen have been identified based on the reaction of established check cultivars. A majority of alfalfa cultivars grown in regions where A. euteiches is prevalent have resistance to race 1 of the pathogen, but very few cultivars have resistance to race 2. The genetic basis of resistance in alfalfa to A. euteiches is unknown, in part due to characteristics of alfalfa that impede genetic analysis, including its tetraploid genome and susceptibility to inbreeding depression. The barrel medic, Medicago truncatula, has been suggested as a model organism for the study of legume genetics. Our objective was to evaluate plant introduction (PI) accessions of M. truncatula for resistance to A. euteiches race 2. In repeated experiments, employing standardized testing conditions used for evaluating resistance in alfalfa to A. euteiches, we identified seven M. truncatula accessions with levels of resistance similar to the resistant alfalfa check population WAPH-5. Two M. truncatula accessions were identified that were as susceptible as the susceptible alfalfa check cultivar Saranac. The utility of M. truncatula as a model for studying the genetics of resistance in alfalfa to A. euteiches race 2 is discussed.