Priyadarisini V Brindha, Gnanamanickam S S
Center for Advanced Studies in Botany, University of Madras, Chennai, India 600 025.
Plant Dis. 1999 Aug;83(8):781. doi: 10.1094/PDIS.1999.83.8.781B.
About 200 isolates of the bacterial blight pathogen Xanthomonas oryzae pv. oryzae were obtained from infected rice (Oryza sativa L.) leaf samples from the Palghat District of Kerala State in southern India during January and February, 1998, when there was a severe epidemic of bacterial blight in the farmers' fields. One hundred and forty of these isolates were assayed for pathogenicity on rice cv. IR24 (no R gene), IRBB21 (Xa21), and NH56 (Xa4+xa5+xa13+Xa21) at their maximum tillering stage by the standard clip-inoculation technique (1) at the Regional Agricultural Research Station (Kerala Agricultural University), Pattambi. In two separate experiments, all the isolates were found to be pathogenic to IR24, producing lesions greater than 10 cm in length. None of the isolates induced susceptible symptoms on cv. NH56 and the average lesion length was less than 2 cm. Twenty of the 140 isolates, however, showed virulence to IRBB21 (seeds supplied by S. R. McCouch, Cornell University, and by P. Ronald, University of California-Davis) and induced lesions of 10.0 to 18.0 cm. We report here the presence of Indian races of X. oryzae pv. oryzae that are virulent to IRBB21 (Xa21), contradicting an earlier report of avirulence (2). These results suggest that the deployment of Xa21 alone will not be a sound strategy for the management of bacterial blight in southern India. References: (1) S. S. Gnanamanickam et al. Plant Dis. 78:173, 1994. (2) G.-L.Wang et al. Mol. Plant-Microbe Interact. 9:850, 1996.
1998年1月和2月期间，印度南部喀拉拉邦帕尔加特地区的稻田里爆发了严重的白叶枯病疫情，从感染白叶枯病的水稻（Oryza sativa L.）叶片样本中分离出了约200株白叶枯病菌（Xanthomonas oryzae pv. oryzae）。在位于帕坦比的区域农业研究站（喀拉拉邦农业大学），采用标准夹接法（1），在水稻品种IR24（无抗病基因）、IRBB21（Xa21）和NH56（Xa4+xa5+xa13+Xa21）的最大分蘖期对其中140株分离菌进行了致病性测定。在两个独立实验中，发现所有分离菌对IR24均有致病性，产生的病斑长度超过10厘米。没有分离菌在品种NH56上诱发感病症状，平均病斑长度小于2厘米。然而，在这140株分离菌中，有20株对IRBB21（种子由康奈尔大学的S. R. McCouch和加利福尼亚大学戴维斯分校的P. Ronald提供）表现出毒力，诱发的病斑长度为10.0至18.0厘米。我们在此报告，存在对IRBB21（Xa21）具有毒力的印度白叶枯病菌小种，这与之前关于无毒力的报道（2）相矛盾。这些结果表明，仅部署Xa21并非印度南部白叶枯病防治的可靠策略。参考文献：（1）S. S. Gnanamanickam等人，《植物病害》78:173，1994年。（2）G.-L. Wang等人，《分子植物-微生物互作》9:850，1996年。
