Pathotypic diversity of Xanthomonas oryzae pv. oryzae, and stringent evaluation of resistance lines of Rice in Bangladesh

Xanthomonas oryzae pv. oryzae ( Xoo ) poses a major risk to worldwide rice cultivation due to its ability to cause bacterial blight (BB). Identifying the Xoo race patterns, and using resistant genes specific to a particular race is a promising strategy to develop varieties with durable resistance. In the present research, 300 Xoo isolates were confirmed and purified from 40 rice-producing areas of Bangladesh to determine the existing races/pathotypes of Xoo . The sensitive rice varieties IR24, BRRI dhan49, and Purbachi showed susceptible reactions against the tested isolates. Fourteen monogenic differentials and 18 pyramid lines were challenged against 300 isolates of Xoo . Bacterial blight resistance genes Xa1 , Xa2 , Xa3 , Xa4 , xa5 , Xa7 , xa8 , Xa10 , Xa11 , xa13 , Xa14 , Xa21 , Xa23 , and Xa27 were found in each monogenic differential. By analyzing patterns of the reaction of 300 Xoo isolates on monogenic differentials, 13 pathotypes/races were determined. The effectiveness of the host plant R genes Xa4 , xa5 , Xa7 , xa8 , Xa10 , xa13 , Xa14 , Xa21 , and Xa27 against bacterial blight has been determined by analyzing frequency resistances and the responses of near isogenic and pyramid lines. Races 1, 3, and 6 were dominantly widespread across the country and were regarded as important races since they had the greatest number of isolates (25%, 23.33%, and 9.67% respectively). Race 2 was the most ubiquitous among the pathotypes, whereas Race 3 was the most virulent, having circumvented every evaluated resistance gene. The bacterial-blight resistant R genes Xa21 and Xa27 have shown resistance against eight and ten races out of thirteen different races, respectively (i.e., 54.7 and 44.3% of the isolates tested). In the evaluation of 50 pyramid lines against the 5 most virulent races, the combinations of Xa4, Xa7, xa13, and Xa21 or the combinations of Xa4, xa5, Xa7, xa13, and Xa21 genes were effective. At present, the suitable and effective R genes i.e., xa5 , Xa7 , xa8 , xa13 , Xa21 , Xa23, and Xa27 could be utilized for the development of a durable BB-resistant variety in Bangladesh.