To understand the molecular basis of broadspectrum resistance to rice blast, fine-scale mapping of the two blast resistance (R) genes, Pi9(t) and Pi2(t), was conducted. These two genes were introgressed from different resistance donors, previously reported to confer resistance to many blast isolates in the Philippines, and were mapped to an approximately 10-cM interval on chromosome 6. To further test their resistance spectrum, 43 blast isolates collected from 13 countries were used to inoculate the Pi2(t) and Pi9(t) plants. Pi9(t)-bearing lines were highly resistant to all isolates tested, and lines carrying Pi2(t) were resistant to 36 isolates, confirming the broad-spectrum resistance of these two genes to diverse blast isolates. Three RAPD markers tightly linked to Pi9(t) were identified using the bulk segregant analysis technique. Twelve positive bacterial artificial chromosome (BAC) clones were identified and a BAC contig covering about 100 kb was constructed when the Pi9(t) BAC library was screened withone of the markers. A high-resolution map of Pi9(t) was constructed using BAC ends. The Pi2(t) gene was tightly linked to all of the Pi9(t) markers in 450 F2 plants. These data suggest that Pi9(t) and Pi2(t) are either allelic or tightly linked in an approximately 100-kb region. The mapping results for Pi9(t) and Pi2(t) provide essential information for the positional cloning of these two important blast resistance genes in rice.
為了了解稻瘟病廣譜抗性的分子機(jī)制，本研究對兩個稻瘟病抗性基因Pi9(t)和Pi2(t)進(jìn)行精細(xì)定位。這兩個基因分別來自不同的抗源，之前有報道對許多菲律賓的稻瘟病菌株具有抗性，并定位到第6染色體上約10-cM的區(qū)間。為了進(jìn)一步檢測Pi9(t)和Pi2(t)的抗譜，用自13個國家收集的43株稻瘟病菌株進(jìn)行接種鑒定。帶有Pi9(t)的株系對所有菌株具有抗性，帶有Pi2(t)的株系對其中36個菌株具有抗性，證明這兩個基因?qū)Φ疚敛【哂袕V譜抗性。通過批量分離分析技術(shù)找到3個與Pi9(t)緊密連鎖的RAPD標(biāo)記。通過其中一個標(biāo)記篩選Pi9(t) BAC庫并鑒定出12個陽性克隆，其中一個BAC重疊群覆蓋了約100kb長度。利用BAC克隆末端構(gòu)建了Pi9(t)的高分辨率圖譜。Pi2(t)在所有450個F2植株上與Pi9(t)的標(biāo)記連鎖，這表明Pi9(t)和Pi2(t)為等位基因或者在約100-kb區(qū)段內(nèi)緊密連鎖。Pi9(t)和Pi2(t)的定位結(jié)果為進(jìn)一步克隆這兩個重要的水稻抗稻瘟病基因提供了必要的信息。