Population Structure of the Rice Blast Fungus in Japan Examined by DNA Fingerprinting.

Abstract

DNA fingerprinting with multilocus probes, MAGGY and MGR586, was conductedto investigate the population structure of the rice blast fungusMagnaporthe grisea in Japan. Two-hundred seventy-eight field isolatescollected during 1993-1997 and 22 archival isolates collected in1976 from various cultivars and locations were examined. Two fingerprintgroups were identified at the 70% similarity level in each collection.A one-to-one correspondence was found between the groups in fieldisolates and the groups in archival isolates. These results suggestthat two discrete lineages exist in the rice blast population. Theywere temporarily designated as JL1 and JL2(Japanese Lineage). JL1was a predominant lineage representing 97% and 77% of the field andarchival isolates, respectively, and present throughout Japan. Inaddition, these two lineages corresponded to two of the five lineagespreviously detected in collections made before 1960, suggesting thatthe structure of the rice blast population in Japan had drasticallychanged during 1960-1976. The two lineages showed a very similarvirulence spectrum, and no relationship could be recognized betweenlineages and pathotypes. MAGGY revealed robust groups which weresimilar to those revealed by MGR586, although the two elements differin character and structure, suggesting that MAGGY could be used asan alternative probe for monitoring the population dynamics of therice blast pathogen.