VIEW ARTICLE

Reaction of Downy Mildew-Resistant Lettuce Cultivars to Infection by Turnip Mosaic Virus. F. W. Zink, Specialist in the Experiment Station, Department of Vegetable Crops, University of California, Davis 95616; James E. Duffus, Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, Agricultural Research Station, Salinas, California 93901. Phytopathology 65:243-245. Accepted for publication 16 September 1974. DOI: 10.1094/Phyto-65-243.

Lettuce cultivars resistant to one or more Bremia lactucae races in Israel or The Netherlands were assayed for reaction to the California race of B. lactucae and to turnip mosaic virus (TuMV). Forty-three cultivars resistant to one or more Israeli or Netherlands races were resistant to U.S. race 5 which is prevalent in California. By using the world lettuce cultivar differentials for identifying races of B. lactucae, we found U.S. race 5 to be different from British races W1, W2, and W3; Israeli races 1, 2, and 4; and Netherlands races 1, 2, 3, and 4. Israeli race 3 and U.S. race 5 appear to be similar. Downy mildew-resistant, TuMV-susceptible cultivars were restricted to the crisphead type. Cultivars Calicel, Calmar, Calmaria, E-4, Imperial 410, Imperial Triumph, Montemar, Monterey, Valrio, Valtemp, and Valverde were mildew-resistant and TuMV-susceptible. The crisphead cultivar Avoncrisp was resistant to both mildew and TuMV. Twenty-seven butterhead type cultivars, two leaf types, one cos type, and one Latin type were resistant, both to U.S. race 5 of B. lactucae and to TuMV. The genetic relationships of mildew-resistant and TuMV-susceptible cultivars are discussed.