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One of Two Major Paralogs of AVR-Pita1 Is Functional in Japanese Rice Blast Isolates

June 2010 , Volume 100 , Number  6
Pages  612 - 618

Mami Takahashi, Taketo Ashizawa, Kazuyuki Hirayae, Jouji Moriwaki, Teruo Sone, Ryoichi Sonoda, Masako Tsujimoto Noguchi, Susumu Nagashima, Kouji Ishikawa, and Michiyoshi Arai

First, second, third, and fourth authors: National Agriculture and Food Organization, National Agricultural Research Center, Hokuriku Research Center, 1-2-1 Inada, Joetsu, Niigata, 943-0193, Japan; fifth author: Research Faculty of Agriculture, Hokkaido University, Sapporo, Hokkaido, 060-8589, Japan; sixth author: National Agriculture and Food Organization, National Institute of Vegetable and Tea Science, Shimada, Shizuoka, 428-8501, Japan; seventh author: National Institute for Agro-Environmental Sciences, Kannondai, Tsukuba, Ibaraki, 305-8604, Japan; eighth author: Shimane Agricultural Technology Center, Ashiwata 2440, Izumo, Shimane, 693-0035, Japan; ninth author: Niigata Agricultural Research Institute, 857 Nagakura, Nagaoka, Niigata, 940-0826, Japan; and tenth author: National Agriculture and Food Organization, National Agricultural Research Center for Kyushu Okinawa Region, 2421 Suya, Koshi, Kumamoto 861-1192, Japan.

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Accepted for publication 26 February 2010.

We analyzed the avirulence gene AVR-Pita1 in Japanese rice blast isolates to determine how they gain virulence toward rice cultivars containing the Pita resistance gene. An avirulent isolate, OS99-G-7a (G7a), from a Japanese commercial field contained two paralogs of AVR-Pita1, designated as AVR-Pita1JA and AVR-Pita1JB. Analysis of virulent, independent mutants derived from G7a, a single avirulent progenitor strain, indicated that AVR-Pita1JA was functional but AVR-Pita1JB was nonfunctional. The most frequent mutation was loss of AVR-Pita1JA. Analyses of field isolates collected from diverse areas in Japan revealed that most of the AVR-Pita1 genes carried by Japanese isolates were identical to AVR-Pita1JA or AVR-Pita1JB. The relationship between these major paralogs in Japanese isolates and the virulence of the strains carrying them indicate that AVR-Pita1JA is functional but AVR-Pita1JB is not, as is the case in G7a. Isolates that show virulence toward rice cultivars containing the Pita gene are presumed to have evolved virulence from avirulent origins via loss of AVR-Pita1JA, except for one case in which virulence resulted from a base substitution. In this study, we discuss the properties and specificities of Japanese rice blasts that relate to virulence against Pita-containing rice. Furthermore, we present a method to amplify AVR-Pita1JA and AVR-Pita1JB separately and, specifically, to monitor functional AVR-Pita1 in Japan.

Additional keywords:Magnaporthe oryzae, Pyricularia oryzae.

© 2010 The American Phytopathological Society