Xanthomonas oryzae pv oryzae, the causative pathogen of bacterial leaf blight (BB) disease is one of the most prevalent rice diseases in Malaysia. Breeding for resistance requires information on the pathogenic variability of X. oryzae for decision-making on the deployment of appropriate resistance genes. In this study, nine Near Isogenic rice Lines (NILs) carrying single BB resistance genes (Xa) used to characterize the virulence of 40 X. oryzae isolates collected from Malaysian rice granaries. The results revealed a highly diverse pathogenic profile, consisting of 21 distinct X. oryzae races named R1 to R21. Race R20, followed by R16 were identified as dominant, showing the highest frequency. Although no Xa genes have been used in Malaysian rice granaries up to now, unexpectedly race R20 was found virulent to most of the NILs carrying the Xa genes. However, the wide distribution of avirulence gene avrxa5 and avrXa7 among the isolates indicated that the population was most effective to NILs carrying the xa5 and Xa7 genes. The information obtained helps to understand the virulence of X. oryzae population and facilitates an adequate gene deployment to increase BB disease resistance in Malaysia.

米糠黄单胞菌（Xanthomonas oryzae pv oryzae）是细菌性叶枯病（BB）病的致病性病原体，是马来西亚最流行的水稻病之一。抗性育种需要有关米曲霉病原性变异性的信息，以决定适当抗性基因的部署。在这项研究中，九个携带单个BB抗性基因（Xa）的近等基因水稻品系（NIL）用于表征从马来西亚水稻粮仓中收集的40个米曲霉菌株的毒力。结果显示，病原体高度多样，由21种不同的米曲霉组成。比赛名为R1至R21。种族R20，其次是R16被确定为主导，显示出最高的频率。尽管到目前为止，马来西亚大米粮仓中都没有使用过Xa基因，但出乎意料的是，发现R20种族对大多数携带Xa基因的NIL都具有毒性。但是，无毒力基因avrxa5和avrXa7在分离物中的广泛分布表明，该种群对携带xa5和Xa7基因的NIL最有效。获得的信息有助于了解米曲霉种群的毒力，并促进适当的基因部署以增加马来西亚的BB病抗性。