Inheritance of resistance to sunflower downy mildew races 1, 2 and 3 in cultivated sunflower

Sunflower downy mildew (SDM) caused by Plasmopara halstedii, is a major disease of sunflower Eleven resistance genes have been identified, but allelic relationships among these genes are not clear. This study examined the inheritance and allelic relationships of genes conferring resistance to SDM races 1, 2 and 3 (virulence phenotypes 100, 300 and 700, respectively) and confirmed a twelfth resistance gene. Three USDA Flant Introductions, AMES 3235, PI 497250, and PI 497938, and three released lines, RHA 266, RHA 274 and DM-2 were Studied. RHA 266 has only the Pl(1) gene for race I resistance. Digenic inheritance of resistance was found in AMES 3235, PI 497250, and RHA 274, These lines have the Pl(1) and Pl(12) genes, conferring resistance to race 1, and the Pl(2) and Pl(11) genes, conferring resistance to race 2. DM-2 and PI 497938 have Pl(12) (but not Pl(1)) for resistance to race 1, the Pl(12) gene (but not the Pl(2)) for resistance to race 2, and Pl(5) for resistance to race 3. These resistance genes will serve as a foundation for future gene designations and genetic diversity studies of resistance to SDM.