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Inheritance of Downy Mildew Resistance in Two Plant Introductions of Lactuca sativa. Luis Sequeira, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706; J. B. Raffray, Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 61:578-579. DOI: 10.1094/Phyto-61-578.

Resistance to lettuce downy mildew (Bremia lactucae) was detected in the field in two plant introductions (P.I. 164937 and P.I. 164939) of Lactuca sativa. Resistance was confirmed in seedlings inoculated in a dew chamber and grown for 6 days in the growth room. Segregation for disease reaction in seedling progenies from susceptible × resistant crosses indicated that resistance is controlled by a single dominant gene in both cases. P.I. 164937 is resistant to all the races of Bremia lactucae prevalent in Wisconsin; P.I. 164939, however, is susceptible to a new race of the fungus that appeared in 1968.