One of two major paralogs of AVR-Pita1 is functional in Japanese rice blast isolates.
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-Pita1(JA) and AVR-Pita1(JB). Analysis of virulent, independent mutants derived from G7a, a single avirulent progenitor strain, indicated that AVR-Pita1(JA) was functional but AVR-Pita1(JB) was nonfunctional. The most frequent mutation was loss of AVR-Pita1(JA). 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-Pita1(JA) or AVR-Pita1(JB). The relationship between these major paralogs in Japanese isolates and the virulence of the strains carrying them indicate that AVR-Pita1(JA) is functional but AVR-Pita1(JB) 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-Pita1(JA), 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-Pita1(JA) and AVR-Pita1(JB) separately and, specifically, to monitor functional AVR-Pita1 in Japan.
Takahashi
Mami
M
National Agriculture and Food Organization, Hokuriku Research Center, Joetsu, Niigata, Japan. mamitaka@affrc.go.jp
Ashizawa
Taketo
T
Hirayae
Kazuyuki
K
Moriwaki
Jouji
J
Sone
Teruo
T
Sonoda
Ryoichi
R
Noguchi
Masako Tsujimoto
MT
Nagashima
Susumu
S
Ishikawa
Kouji
K
Arai
Michiyoshi
M
D005798:Genes, Bacterial; D017343:Genes, Plant; D054884:Host-Pathogen Interactions; D007564:Japan; D020082:Magnaporthe / Q000235:genetics / Q000472:pathogenicity*; D009154:Mutation; D012275:Oryza / Q000235:genetics / Q000276:immunology / Q000382:microbiology*; D016133:Polymerase Chain Reaction; D014774:Virulence