CHARACTERIZATION OF PHYTOPHTHORA-INFESTANS IN WISCONSIN FROM 1993 TO 1995

Late blight of potato (Solanum tuberosum), caused by Phytophthora infe stans, recently reappeared in Wisconsin and was a significant producti on problem in 1994. P. infestans isolates collected in Wisconsin from 1993 to 1995 were characterized for the following traits: mating type, sensitivity to metalaxyl, and allozyme genotype for Glucose-6-phospha te isomerase (Gpi). Characterization of these isolates revealed that a new, more aggressive population (A2 mating type, metalaxyl resistant, and Gpi genotype 100/111/122) is displacing the old population (A1 ma ting type, metalaxyl sensitive, and Gpi genotype 86/100) in Wisconsin.