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.