Laboratory-Induced Resistance to Fosetyl-Al in a Metalaxyl-Resistant Field Isolate of Pythium aphanidermatum. P. L. Sanders, Associate Professor of Plant Pathology, The Pennsylvania State University, University Park 16802. M. D. Coffey, G. D. Greer, and M. D. Soika. Professor of Plant Pathology, Staff Research Associate, Department of Plant Pathology, University of California, Riverside 92521; and Senior Research Aide, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Plant Dis. 74:690-692. Accepted for publication 1 March 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0690.

Mutants of Pythium aphanidermatum resistant to both metalaxyl and fosetyl-Al were obtained following exposure of a metalaxyl-resistant field isolate to the chemical mutagen N-methyl-N’-nitro-N-nitrosoguanidine. Selected mutants were resistant to metalaxyl and phosphorous acid in vitro and exhibited in vitro growth rates and zoospore production that differed little from the metalaxyl-resistant parent. Mutants were resistant to metalaxyl and fosetyl-Al on greenhouse-grown Penncross creeping bentgrass and showed virulence equal to that of the parental isolate.