Submitted to: Proceedings of Brassica
Publication Type: Abstract Only
Publication Acceptance Date: 7/20/2000
Publication Date: 9/5/2000
Citation: Farnham, M.W., Wang, M., Thomas, C.E. 2000. Elucidation of genes controlling downy mildew in broccoli. Brassica 2000 abstract. Wellesbourne, U.K. 0515.
Technical Abstract: Downy mildew is one of the most destructive diseases of broccoli and other Brassica oleracea L. crops. This fungal disease, caused by the biotrophic parasite Peronospora parasitic (Pers. Fr.) Fr. has worldwide distribution. Fungicide application can provide control of downy mildew in broccoli. However, the use of resistant broccoli cultivars is an alternative control method that could provide a practical, long-term, and environmentally- benign means to limit damage due to this disease. We have an ongoing program to develop doubled-haploid (i.e., homozygous) lines of broccoli that express high levels of downy mildew resistance and that may serve as inbred parents for development of resistant F1 hybrids. Among our developed lines, we have identified doubled-haploid lines that are susceptible at the cotyledon stage but highly resistant at the true-leaf stage and others that are highly resistant at cotyledon as well as true-leaf stages. Our long term goal is to elucidate genes for downy mildew resistance. To study inheritance of the different downy mildew resistance phenotypes we have identified, resistant lines were crossed to a susceptible line, and conventional (e.g., F2 and backcross) and doubled-haploid populations were developed from the resulting F1 hybrids. These populations were evaluated for response to inoculation with P. parasitica. Inheritance of true-leaf stage resistance was determined to be controlled by two complementary dominant genes. This mode of inheritance was confirmed in both conventional and doubled-haploid populations. A RAPD marker linked to the true-leaf stage resistance has been identified and sequenced. Initial tests indicate that cotyledon stage resistance exhibits dominance.