Rice blast disease, caused by Magnaporthe oryzae, is one of the most importance diseases of rice production worldwide. The key role of defense mechanism to combat this fungus in rice follows the gene-for-gene concept, which a plant resistant (R) gene product recognizes a fungal avirulent (AVR) effector and triggers the hypersensitive response. However, the AVR genes have been shown to be rapidly evolving resulting in high level of genetic diversity. The aims of this study were to examine the nucleotide sequence variation of AVR-Pita1 gene in Thai rice blast isolates and to identify the severity of blast disease using isogenic line of Pita gene. Seventy-six rice blast isolates collected from different parts of Thailand were used. Gene specific primers for AVR-Pita1 gene coding sequence were designed and used for identifying the genetic diversity of AVR-Pita1 gene by PCR amplification and sequencing. The obtained sequences were analysed for genetic variation and genetic relationship. Our results revealed the association between the sequence variations of AVR-Pita1 and selective forces from Pita gene. This phenomenon demonstrated the coevolution between rice blast resistant gene in rice and avirulent gene in blast fungus. The information about variation and evolutionary mechanisms of AVR gene obtained from this study can be used in rice blast resistant breeding programme.

中文翻译：

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泰国稻瘟病菌群体中无毒基因 AVR-Pita1 的高核苷酸序列变异

由稻瘟病菌引起的稻瘟病是全球水稻生产中最重要的病害之一。在水稻中对抗这种真菌的防御机制的关键作用遵循基因对基因的概念，即植物抗性 (R) 基因产物识别真菌无毒 (AVR) 效应子并触发过敏反应。然而，AVR 基因已被证明正在快速进化，从而导致高水平的遗传多样性。本研究的目的是检查泰国稻瘟病分离株中 AVR-Pita1 基因的核苷酸序列变异，并使用 Pita 基因的等基因系确定稻瘟病的严重程度。使用了从泰国不同地区收集的 76 株稻瘟病菌株。设计了AVR-Pita1基因编码序列的基因特异性引物，用于通过PCR扩增和测序鉴定AVR-Pita1基因的遗传多样性。分析获得的序列的遗传变异和遗传关系。我们的结果揭示了 AVR-Pita1 的序列变异与来自 Pita 基因的选择力之间的关联。这一现象证明了水稻抗稻瘟病基因与稻瘟病真菌无毒基因之间的共同进化。本研究获得的AVR基因变异和进化机制信息可用于稻瘟病抗性育种计划。我们的结果揭示了 AVR-Pita1 的序列变异与 Pita 基因的选择力之间的关联。这一现象证明了水稻抗稻瘟病基因与稻瘟病真菌无毒基因之间的共同进化。本研究获得的AVR基因变异和进化机制信息可用于稻瘟病抗性育种计划。我们的结果揭示了 AVR-Pita1 的序列变异与 Pita 基因的选择力之间的关联。这一现象证明了水稻抗稻瘟病基因与稻瘟病真菌无毒基因之间的共同进化。本研究获得的AVR基因变异和进化机制信息可用于稻瘟病抗性育种计划。