探究臺灣稻熱病菌AvrPiz-t和AvrPib基因的動態變化

Abstract

由絲狀真菌Magnaporthe oryzae分生孢子侵染水稻而引起的稻熱病，在每年投入大量的科研及防治經費之餘，仍造成全球數以千萬噸計水稻生產上的損失。自從美國科學家Flor提出“基因對基因”的假說，引入抗性基因培育新的水稻抗性品種，被視為最經濟有效、且環境友善的對抗稻熱病的方法。然而新的水稻抗性品種在推廣商業化種植後，田間抗性往往在一兩年就大幅下降，過往研究認為這一問題的主要原因是稻熱病菌無毒基因的快速變異所致。本研究通過發展iiPCR快速檢測技術，應用於臺灣各地田間稻熱病菌AvrPiz-t基因狀況之篩檢，並藉由Pot2指紋圖譜的特徵分析，鑒別區分不同生理小種的族群。同時，藉由收集過往年份臺灣不同地區水稻品種種植分佈及抗性資訊，分析比對對應地區採集及分離稻熱病菌AvrPiz-t基因的突變狀態，探討稻熱病菌生理小種AvrPiz-t基因在臺灣地區的演替過程。此外，我們也初步分析臺灣稻熱病菌AvrPib基因之狀況，藉以瞭解其變異特徵。本研究藉由瞭解AVR基因的變異及動態變化，期望作為病害發生預測及新抗性水稻育種及品種推廣的資訊。

Rice blast disease is caused by the filamentous ascomycete Magnaporthe oryzae. This fungus produces asexual spores, which differentiate into appressoria enabling penetration rice cuticle for infection. Although tremendous amount of money has been used to study and manage this disease, tens of millions tons of rice loss still occur annually. Since the “gene-for-gene” theory proposed by Flor, resistance (R) gene mediated resistance has been considered to be one of the most economical, efficient and environment friendly strategies to prevent the disease. However, the resistance of newly introduced R gene is usually overcome within one or two years shortly after their release, which resulting from the high variability of avirulence (AVR) gene in blast population. In this study, we aim to first develop iiPCR method to quickly investigate the status of AvrPiz-t gene using diseased leaf samples from the fields. In combination of Pot2 fingerprinting analysis, we hope to differentiate physiological races among Taiwan blast population. To reveal the evolution of AvrPiz-t gene, we confirmed the Piz-t resistance gene among the commercial elite rice varieties and their distribution in Taiwan. In addition to AvrPiz-t gene, we also characterized the status and variability of AvrPib gene among blast population. We hope to provide useful information for disease forecasting and resistance breeding and deployment strategies.