Spatial and temporal genotypic changes in Japanese isolates of
Phytophthora infestans (1997-2007)
S. Akino1, M. Kato2, Y. Baba1, D. Hirotomi1, K. Mizunuma1, H. Hagiwara1 and
N. Kondo1
Until 1996, the Phytophthora infestans genotype JP-1 (mating type A2) was dominant in the
Japanese potato late blight pathogen population, while the genotype US-1 was driven away. After
1997, new A1 mating-type genotypes were recognized and named JP-2, JP-3, JP-4, and other
derived genotypes, based on information on isozymes, RG57 DNA fingerprints, and mitochondrial
DNA haplotypes. It was proposed that JP-2 migrated from a foreign country into Japan, while JP-3
and JP-4 arose inside Japan via sexual reproduction. From 1997 to 2003, most of the P. infestans
genotypes in Japan were JP-1, JP-2, JP-3, and JP-4. Subsequently, JP-1 and JP-3 diminished in
the northern part of Japan (Hokkaido Island) until 2007, while JP-1 persisted in the southern parts
(Kanto district and Kyushu Island) of Japan until 2007. The foliar aggressiveness of JP-1, JP-2,
JP-3, and JP-4 was estimated using a leaf-disk test with susceptible potato varieties (Irish
Cobbler and Toyoshiro). There were no remarkable differences in the latent period, infection
efficiency, or sporulation intensity in highly aggressive isolates of Japanese genotypes, or a
standard European isolate. To explain the cause of genotypic changes in Japan, it will be
necessary to investigate the viability and competitiveness of these isolates in the field.
1
Laboratory of Plant Pathology, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan; 2National
Agricultural Research Center, NARO, 3-1-1 Kannondai, Tsukuba 305-8666, Japan