Characterization of the Phytophthora infestans population in the Columbia Basin of Oregon and Washington from 1992 to 1995

Isolates of Phytophthora infestans collected from 1992 to 1995 from potato fields in the Columbia Basin of Oregon and Washington were analyzed for compatibility type, metalaxyl sensitivity, and glucose-6-phosphate isomerase (Gpi) genotype. In 1992, 30 of 31 isolates were of the US-I multilocus genotype. A single metalaxyl-resistant isolate of the US-6 (Al Gpi 86/100) genotype was found near the end of the growing season. In 1993, only 2 of the 59 isolates collected were Al isolates with Gpi 86/100. Ten isolates were of the A2 compatibility type, seven with Gpi 100/111, two with Gpi 100/100, and one was undetermined. The remaining isolates were metalaxyl-resistant Al compatibility types with either Gpi 100/100 or 100/111. The first A2 isolates in the Columbia Basin were found in 1993. In 1994, 10 of 18 isolates were of the US-I genotype. The remaining isolates were US-6 and US-8 genotypes. In 1995, 97% of 268 isolates tested were of the US-8 genotype. Five isolates were A2 compatibility type with Gpi 100/122. One A2, metalaxyl-resistant isolate was Gpi 100/100/111, and two Al isolates were Gpi 100/111/122. The population of P. infestans quickly changed between 1992 and 1995, from a population comprised almost exclusively of the US-I genotype to a population represented by new or recombinant genotypes.