Distribution of Phytophthora infestans Populationsin Seven Asian Countries.

Abstract

The mating type, allozyme genotypes of malic enzyme, glucose-6-phosphate isomerase and peptidase loci, and metalaxyl sensitivity of 336 Phytophthora infestans isolates collected in Korea, India, Taiwan, Indonesia, Thailand, Nepal, and China between 1992 and 1997 were determined. Only A1 mating type isolates were detected in India and Taiwan, and only A2 isolates in Korea and Indonesia, while both mating type isolates were detected in Thailand, Nepal, and China. The isolates from Korea, India, Taiwan, and Indonesia had a single allozyme genotype respectively, while the isolates from Thailand, Nepal, and China had two or three allozyme genotypes. Isolates that were highly resistant to metalaxyl were found in Korea, Indonesia, and China. All of the isolates from Taiwan and India, and some of the isolates from Thailand, Nepal, and northern and southern areas of China, belonged to the old population of P. infestans, which was predominant worldwide until the appearance of A2 isolates outside central Mexico. Some of the isolates from Thailand and Nepal were from new populations that have been discovered since the appearance of A2 isolates outside central Mexico. All of the isolates from Korea and Indonesia and most of the isolates from China belonged to two specific populations, which have been rarely detected elsewhere. The occurrence of these separate populations in Asia suggests that they followed a different migration pathway, or that they are better adapted to Asian conditions than to those elsewhere in the world.