Characterization of Japanese Rhizoctonia solani AG-2-1 isolates using rDNA-ITS sequences, culture morphology, and growth temperature
Rhizoctonia solani AG-2-1 is classified into three subsets (Subsets 1–3) based on the rDNA-ITS sequence. Few Japanese isolates, however, have been phylogenetically analyzed. To understand the distribution and diversification of AG-2-1 isolates in Japan, we examined 23 Japanese AG-2-1 isolates (15 from Hokkaido, the northernmost island, and eight from NARO Genebank) in terms of rDNA-ITS sequences, culture morphology, and temperature-dependent growth characteristics. Of these, 15 isolates were found to belong to Subset 1. One isolate, which formed a light brown colony with concentric rings and grew slowly at 25 °C, was classified into Subset 2. Six isolates had varied culture morphology and relatively faster growth than Subset 1 isolates at 30 °C. They formed a clade on the phylogenetic tree, designated clade HK, with cauliflower isolates from Belgium and the Netherlands, with a bootstrap value of 47%, and were separate from the three known subsets. Sequence similarity in the rDNA-ITS region for this clade ranged from 98.2 to 100%, whereas clade HK isolates had 96.7–98.6% similarity with the isolates in each subset. This result suggests that clade HK is likely an independent intragroup within AG-2-1, although the rDNA-ITS sequences in this clade were variable. One isolate was not assignable to any clade because it was intermediate between isolates in clade HK and Subset 2. This is the first report describing variation among rDNA-ITS sequences of Japanese AG-2-1 isolates.
KeywordsAG-2-1 Clade HK Japan rDNA-ITS Rhizoctonia solani Sequence variation
This work was supported by the Cabinet Office, Government of Japan, Cross-ministerial Strategic Innovation Promotion Program (SIP), “Technologies for creating next-generation agriculture, forestry and fisheries” (funding agency: Bio-oriented Technology Research Advancement Institution, NARO). We thank Dr. M. Iketani and Mr. T. Kozawa (Hokkadio Research Organization) for providing isolates of R. solani and Dr. S. Kuninaga (Health Sciences University of Hokkaido) for providing valuable insights. We also thank Dr. N. Matsumoto for critically reading the manuscript and correcting the English. Special thanks are due to the Genetic Resources Center, NARO, for providing isolates.
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The authors declare that they have no conflict of interest.
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