VIEW ARTICLE

Ecology and Epidemiology

Parasitic Fitness and Intrastrain Diversity of Benomyl-Sensitive and Benomyl-Resistant Subpopulations of Venturia inaequalis. N. Lalancette, Graduate research assistant, Department of Plant Pathology, The Pennsylvania State University, Fruit Research Laboratory, Biglerville, PA 17307, Present address: Postdoctoral research associate, Department of Plant Pathology, The Ohio State University, Ohio Agricultural Research and Development Center, Wooster 44691; K. D. Hickey(2), and H. Cole, Jr.(3). (2)Professor, Department of Plant Pathology, The Pennsylvania State University, Fruit Research Laboratory, Biglerville, PA 17307; (3)Professor, Department of Plant Pathology, The Pennsylvania State University, University Park, PA 16802. Phytopathology 77:1600-1606. Accepted for publication 30 April 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-1600.

Benomyl-sensitive and -resistant strains of Venturia inaequalis were isolated from two commercial apple orchards. In a greenhouse study, four fitness parameters (incubation period, colonization, sporulation, and infection efficiency) were measured on potted McIntosh apple trees infected with the isolates. The resistant and sensitive isolates from one orchard (Schultz) were not significantly different for three of the four fitness parameters. However, the resistant isolates from a second orchard (Barnard) were less fit than the sensitive isolates for all but one fitness parameter. Similarly, the relative fitness parameters, derived from a multiplicative model, were not statistically different for the two isolate types in the Schultz orchard but were different for those in the Barnard orchard. We hypothesize that removal of benomyl from the spray program in the Barnard orchard may allow reversion of the population to sensitivity, whereas this would not occur for the Schultz orchard. Unlike the means, the diversities (Simpson’s Diversity Index) of the two subpopulation samples from each orchard were less definitive and dependent on interpretation of the cluster analysis performed.