SELECTION AND CHARACTERIZATION OF INHIBITOR-RESISTANT MUTANTS OF PHYTOPHTHORA-SOJAE

Bhat, R. G., and Schmitthenner, A. F. 1993. Selection and characterization of inhibitor-resistant mutants of Phytophthora sojae. Experimental Mycology 17, 109-121. Selectable markers, resistance to metalaxyl (MEX) and p -fluorophenylalanine (FPA), were induced in Phytophthora sojae races by treating zoospores with N -methyl-N′-nitro-N′-nitrosoguanidine. Calcium treatment enhanced the percentage encystment of zoospores. MEX-resistant (MEXr) and FPA-resistant (FPAr) mutants were selected on a lima bean agar medium containing MEX (10 μg/ml) and FPA (50 μg/ml), respectively. A number of single inhibitor-resistant mutants were obtained. There was variation in in vitro growth of mutants. Virulence of mutants was evaluated by hypocotyl inoculation of soybean cultivars with Rps 1 (Amsoy 71), Rps1-c (Williams 79), Rps1-k (Williams 82), or rps1 (Williams) alleles. It was observed that the 23% of the MEXr and 33% of the FPAr mutants had a different virulence pattern than the original cultures. © 1993 Academic Press. All rights reserved.