Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2002
Publication Date: 8/21/2002
Citation: Farnham, M.w., Wang, M., Thomas, C.E. A single dominant gene for downy mildew resistance in broccoli. Euphytica. 2002. v.128.p.405-407. Interpretive Summary: Downy mildew is one of the most destructive diseases of broccoli and is caused by a fungus. Most broccoli producers spray fungicides to control this disease. Due to concerns about the negative effects of pesticides on the environment and as residues on vegetables, we have developed varieties of broccoli that have natural resistance to downy mildew and that do not require fungicide sprays to prevent leaf, head and stem infection. The goal of this research was to determine how resistance is inherited in one of these varieties. This is necessary so that we can devise strategies for breeding resistance from this variety into new better ones. To accomplish our goal we crossed a resistant variety with a susceptible variety, developed progenies from this cross, and evaluated the response of the progenies to artificial inoculation and infection by the downy mildew fungus. From these evaluations we determined that a single gene confers downy mildew resistance in the resistant broccoli variety under study. We also determined that the resistance gene is dominant over susceptible genes. This work is of interest to commercial and public breeders attempting to develop improved broccoli hybrids. The resistant variety studied in this work and knowledge of its inheritance will be used by breeders working to create superior hybrids that express high levels of downy mildew resistance that producers can grow without using fungicides.
Technical Abstract: Downy mildew, incited by Peronospora parasitica (Pers.: Fr.) Fr., is a destructive disease of broccoli (Brassica oleracea L., Italica Group). Resistant cultivars represent a desirable control method to provide a practical, environmentally benign, and long-term means of limiting damage from this disease. Doubled-haploid (DH) lines developed by us exhibit a high level of downy mildew resistance at the cotyledon stage. To determine the mode of inheritance for this resistance, a resistant DH line was crossed to a susceptible DH line to make an F1, from which F2 and backcross (BC) populations were developed. All populations were evaluated for response to artificial inoculation with P. parasitica at the cotyledon stage. All F1 plants (including reciprocals) were as resistant as the resistant parent, indicating no maternal effect for this trait. F2 populations segregated approximately 3 resistant to 1 susceptible, BC populations using the resistant parent as the recurrent parent contained all resistant plants, and the BC to the susceptible parent segregated 1 resistant to 1 susceptible. These results indicate that resistance is controlled by a single dominant gene. This gene should be easily incorporated into F1 hybrids and used commercially to prevent downy mildew.