2.2.21
DISTRIBUTIONS OF PHYTOPHTHORA INFESTANS POPULATIONS IN SOME ASIAN COUNTRIES

R NISHIMURA1, K SATO1, WH LEE2, UP SINGH3, T CHANG4, E SURYANINGSIH5, P LUMYONG6, WH TANG7, K SHRESTA8, M KATO9, N FUJII1, S AKINO1, N KONDO1, K KOBAYASHI1 and A OGOSHI1

1HU, Japan; 2CBU, Korea; 3BHU, India; 4TFRI, Taiwan; 5LEHRI, Indonesia; 6CMU, Thailand; 7CAU, China; 8NARC, Nepal; 9HNAES, Japan

Background and objectives
Populations of Phytophthora infestans are characterized by markers, some of which are mating type, allozymes, metalaxyl sensitivity, virulence, nuclear DNA content, nuclear DNA fingerprinting and mitochondrial DNA RFLPs. There are many reports on the distribution, diversity and relationship of P. infestans populations in Europe, the USA and Central and South America but few reports on these in Asia. We had three objectives in this study: the first was to clarify the distribution of P. infestans populations in Asian countries (Korea, India, Taiwan, Indonesia, Thailand, China and Nepal); the second was to compare characteristics of Asian and worldwide populations, and to investigate the relationships among them; and the third was to propose possible migrations and the pathways.

Materials and methods
The 336 isolates used in this study were collected in seven Asian countries from 1992 to 1997. We also used some Japanese, UK and Mexican isolates. These isolates were analysed for mating type, allozyme genotype of malic enzyme, glucose-6-phosphate isomerase and peptidase loci and metalaxyl sensitivity.

Results and conclusions
Only A1 mating type isolates were found in the samples from India and Taiwan and only A2 mating type isolates were found in the samples from Korea and Indonesia. Both mating type isolates were found in the samples from Thailand, China and Nepal. All isolates from tomato were A1 mating type. It was found that all the Taiwanese, 23 of the Thai, one of the Chinese and 46 of the Nepali isolates had the same allozyme genotype that has been detected all over the world and that has dominated most populations until recently. This population of these isolates is named the old population. All the Indian and 18 of the Nepali isolates had the same allozyme genotype that has been detected and spread globally since the 1980s. Thirty-two of the Thai and 34 of the Nepali isolates had the same allozyme genotype that has been detected in central Mexico and Europe and spread since the 1980s. It is postulated that the populations of both the former and latter isolates are the new populations.

All of the Korean and Indonesian isolates had a specific allozyme genotype and the same result was reported elsewhere [1,2]. Because this population has not been detected in most of the world, it is possible that the migration path of this one is different from the others. Most of the Chinese isolates had a specific allozyme genotype; this genotype has previously only been detected in central Mexico and it is possible that the populations have a unique migration or a mutation that occurs post migration.

There was diversity in metalaxyl sensitivity in the isolates used in this study. Most of were metalaxyl-sensitive isolates and all isolates from tomato were sensitive. Metalaxyl-resistant isolates were obtained from Korea, Indonesia and China.

There is no great diversity of P. infestans populations in Asian countries and it is proposed that the populations in Korea, India, Taiwan and Indonesia are single clonal lineages, but those in Thailand, China and Nepal have several clonal lineages. Moreover, it is possible that sexual reproduction occurs in Thailand and China because both mating types were detected in one field.

References
1. Mosa AA, Kobayashi K, Ogoshi A, Kato M, Sato N, 1993. Plant Pathology 42, 26-34.
2. Koh YJ, Goodwin SB, Dyer AT, Cohen BA, Ogoshi A, Sato N, Fry WE, 1994. Phytopathology 84, 922-927.