Resistance of Bipolaris oryzae to Fenapanil. M. K. Kardin, Former Graduate Assistant, Department of Plant Pathology, University of Minnesota, St. Paul 55108. J. A. Percich, Assistant Professor, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Plant Dis. 67:871-874. Accepted for publication 5 January 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-871.

Fenapanil-resistant strains of Bipolaris oryzae were obtained by successive transfers on a series of fenapanil-amended potato-dextrose agar media containing increasing concentrations of the fungicide or by selection from a conidial suspension on a medium containing 100 μg/ml of fenapanil. The ability of the fungus to acquire resistance to fenapanil was accompanied by a reduction in its fitness for survival and virulence. Generally, strains with a greater degree of fenapanil resistance grew slower and produced fewer conidia than strains with less resistance to fenapanil. Most of the fenapanil-resistant strains of B. oryzae declined in their resistance to fenapanil after one passage on a fungicide-free medium. Both fenapanil-resistant and -sensitive strains were effectively controlled on fenapanil-treated plants in the greenhouse; however, the fenapanil-sensitive strain was more virulent on untreated plants.