Inheritance of resistance to stem canker (Phomopsis helianthi) in sunflower

Six male sterile sunflower lines were crossed with seven restorers in a fac torial mating design. The 13 inbred lines and their 42 Fl hybrids were plan ted in a randomized block design with three replicates. Each replicate cons isted of two rows, 5 m long (30-35 plants per replicate). Resistance to nat ural Phomopsis infection, presented as the percentage of plants with no enc ircling necrosis lesions of the fungus on the main stem, was determined at physiological maturity. Analysis of variance showed that female and male ge neral combining abilities (GCA) and specific combining abilities (SCA) of F 1 hybrids were significant. The ratio of additive variance to total varianc e was 0.662, a high value which indicates prevailing additive effects. The additive variance due to females was more important than that of males, pro bably because of the existence of maternal effects or more effective genes for resistance in the female lines used in this experiment. The estimates o f GCA were significant and positive for LC1004A, KO549A, 50KD8 and LC1064C inbred lines. These lines should be considered in developing hybrids with i mproved resistance to Phomopsis in sunflower breeding programmes.