Inheritance of Resistance to Rase 4 of Sunflower Downy Mildew in Wild Sunflower Accessions
- Ahmet S. Tan ,
- Chao-Chien Jan and
- Thomas J. Gulya
Race 4 of sunflower downy mildew (SDM), Plasmopara haistedii (Farl.) Beri. & De Toni in Sacc. was identified in 1985, and currently is prevalent worldwide. Our objectives were to (i) determine the mode of inheritance of resistance to Race 4 (SDM-4) of P. halstedii in wild Helianthus annuus L. accessions PI 413047, PI 413131, PI 413157, and PI 413161, and (ii) study allelic relations of resistance genes these accessions and SDM-4 resistance in line HA 336. Seedlings were classed as resistant (R) or susceptible (S) based on detection of pathogen on cotyledonary or true leaves. Resistant plants from the wild accessions and HA 336 were crossed with susceptible lines HA 89 and cytoplasmic male-sterile (cms) HA 89. Most F1 progenies of wild accessions/HA 89 and cms HA 89/segregated 1R:IS, suggesting that most of the plants selected from wild accessions were heteruzygous for a single dominant gene for resistance to SDM-4. Sogregation ratios of 1R:IS in backcross families confirmed that SDM-4 resistance was inherited as a single dominant gene. Resistant segregates of halfdiallei crosses among resistant F1 plants from different sources were crossed with HA 89 and cms HA 89. Segregation ratios indicated that different resistance genes occur in PI 413047, PI 413131, PI 413157, and PI 413161, and that these genes differ from PP in HA 336. The four genes found in these wild accessions provide unique sources of resistance to the pathogen and, with introgression into cultivated sunflower (H. annuus L.), should reduce genetic vulnerability to this disease.
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