Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 28, 2001
Publication Date: February 1, 2002
Citation: Rahim, M., Jan, C.C., Gulya Jr, T.J. 2002. Inheritance of resistance to sunflower downy mildew races 1, 2, and 3 in cultivated sunflower. Plant Breeding. 121:57-60. Interpretive Summary: Sunflower downy mildew(SDM) is a seed, air, and soil-borne disease of sunflower (Helianthus annuus L.), and is the most prevalent disease in many production areas worldwide. Under certain climate conditions, this obligate parasite can kill 70 to 80% of the plants in a field. New races appear frequently due to the pathogenic variability in the fungus and the selection pressure resulting from the use of resistant sunflower and fungicide seed treatment. The identification of new resistance genes in Helianthus species is essential for insuring protection against existing and evolving virulent SDM races. Information on the inheritance and relationships of SDM resistance genes is limited. Eleven genes have been postulated to confer resistance to the nine identified races of SDM. This study determined the inheritance of resistance to SDM races 1, 2, and 3, in three plant introductions AMES 3235, PI 497250, and PI 497938, and three USDA lines DM-2, RHA 274, and RHA 266, and to determine the allelic relationships among the associated resistance genes. Results of this study will serve as a foundation for similar studies on newly identified resistance genes or gene clusters, and eventually help breeders in developing strategies against this devastating sunflower disease.
Technical Abstract: Sunflower downy mildew (SDM), Plasmopara halstedii (Farl.) Berl and de Toni, is a major diseases of sunflower (Helianthus annuus L.). Eleven genes conferring resistance have been traced to wild Helianthus species. However, allelic relationships among these resistance genes are not clear. This study examined the inheritance and allelic relationships of genes conferring resistance to SDM races 1, 2, and 3. Three USDA plant introductions, AMES 3235, PI 497250, and PI 497938, and three released lines, RHA 274, DM-2, and RHA 266 were studied. Digenic inheritance of resistance was found in AMES 3235, PI 497250, and RHA 274. These lines have the Pl1 and Pl12 genes, conferring resistance to race 1, and the Pl2 and Pl11 genes, conferring resistance to race 2. DM-2 and PI 497938 have Pl11 and Pl12 but lack Pl2. The Pl2 gene in RHA 274, AMES 3235, and PI 497250 conferred resistance to race 2 only. DM-2 and PI 497938 have Pl5 for resistance to race 3. AMES 3235, PI 497250, and RHA 274 have resistance to races 1 and 2 conferred by Pl1, Pl12, Pl2 and Pl11. DM-2 and PI 497938 are resistant to all 3 races and posses Pl12, Pl11, and Pl5. RHA 266 has only the Pl1 gene. These resistance genes will serve as a foundation for future gene designation and genetic diversity studies of resistance for SDM races 1, 2, and 3.