MIGRATIONS AND DISPLACEMENTS OF PHYTOPHTHORA-INFESTANS POPULATIONS IN EAST-ASIAN COUNTRIES

Two clonal lineages of Phytophthora infestans were detected in a sample of 124 isolates collected in China, Japan, Korea, the Philippines, and Taiwan. All isolates were analyzed for mating type, genetic variation at two allozyme loci, glucose-6-phosphate isomerase (Gpi), and peptidase (Pep), nuclear DNA fingerprint as detected with probe RG57, and mitochondrial DNA haplotype. One clonal lineage (A1 mating type, 86/ 100 for Gpi, and 92/100 for Pep) was detected in all five countries and was identical to a genotype found throughout the world, previously designated as US-1. The other genotype, JP-1, was A2 mating type, 100/100 for Gpi and 96/96 for Pep. This genotype has been detected only in recent samples from Korea and Japan, where it is now the predominant genotype. Two variants of the US-1 genotype occurred in the Philippines. Both the US-1 and JP-1 clonal lineages were polymorphic for metalaxyl resistance, indicating that metalaxyl-resistant isolates are probably selected within each clonal lineage in situ. Isolates resistant to metalaxyl were common in the northern part of South Korea, but all isolates tested from the southern part were sensitive. Both A1 and A2 mating type isolates occurred in Korea and Japan, but the A2 genotype appears to be displacing the A1 genotype in both locations. There was no evidence of sexual reproduction in either location.