Pathotype profiling, distribution and virulence analysis of Xanthomonas oryzae pv. oryzae causing bacterial blight disease of rice in Bangladesh

Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is a serious threat to rice production in the world. Identification of Xoo races pattern, distribution and deployment of race-specific resistant genes is a sustainable strategy to develop bacterial blight resistant varieties. In this study, a total of 118 isolates of Xoo were collected from 8 rice-growing regions of Bangladesh to identify the existing pathotypes of Xoo. All tested isolates were virulent on the susceptible rice varieties viz. IR24, Purbachi and BR11. The tested isolates were evaluated on 13 near-isogenic lines of rice and each line consisted of a single bacterial blight resistant gene viz Xa1, Xa2, Xa3, Xa4, xa5, Xa7, xa8, Xa10, Xa11, xa13, Xa14, Xa21 and Xa23. Based on reaction patterns of 118 isolates of Xoo on near-isogenic lines, 12 pathotypes/races were first time identified in Bangladesh. Race 1, Race 2 and Race 3 were predominantly distributed in the most of the areas of Bangladesh and considered as major races containing the maximum number of isolates (48%, 14% and 11% respectively). Among these, Race 1 was the most prevalent and widely distributed while Race 5 was the most virulent circumventing all of the resistance genes tested. Race 1 was recorded from six rice-growing regions of Bangladesh. Host plant R-genes xa5, xa8, xa13, Xa21 and Xa23 have been found as effective against bacterial blight based upon resistance frequencies and the reactions of near-isogenic lines and pyramid lines. The bacterial blight resistant gene Xa21 showed a resistant reaction against 11 of 12 races (i.e. 94.91% of the isolates tested). Effective genes and information of races generated from this study could be deployed for the development of race-specific bacterial blight resistant varieties in Bangladesh.