Breeding for resistance to Sclerotinia sclerotiorum in Brassica oleracea

We screened 382 B. oleracea var. capitata plant introductions from the plants Genetics Resources Unit at Geneva NY. Petri plates of PDA were inoculated with the fungus and grown for 3 days at room temperature. Disks of infected agar were then cut with a #2 cork borer and used for inoculum. Initial screening was done in the greenhouse. Subsequently 80 lines were grown in the field, inoculated with infected agar discs, and irrigated daily to enhance disease. Susceptible plants died 2-3 weeks following inoculation. Resistance was also measured with a detached leaf test: 15 cm sections of petioles or cabbage midribs were placed in moist boxes and inoculated with infected agar discs. Several non heading cabbages, a savoy cabbage and some red cabbage PIs showed good tolerance. Hybrids and back cross populations were developed, planted in the field, and inoculated and scored for disease development. In 1993 most susceptible checks were killed, as were all F1 plants. In the cross of the best non heading cabbage PI 206942 x cabbage and cauliflower, the F2 and back cross populations suggested a major recessive gene for resistance, plus modifiers. Crosses with other sources of resistance gave less definitive results. Heritability for crosses with cabbage and cauliflower respectively was h = 0.82 and 0.58. Heritability based on regression of F3 on F2 were 25 and 26% for crosses involving cauliflower and cabbage and 54% for broccoli.