Diversity and Distribution of Rice Blast ( Cavara) Races in Vietnam.

A total of 239 isolates of blast ( Cavara) collected from northern and central Vietnam showed a wide variation in pathogenicity based on the reaction patterns to 25 differential varieties (DVs) harboring 23 resistance genes and susceptible cultivar Lijiangxintuanheigu (LTH). The frequencies of isolates virulent toward DVs for , , , , , , (t), (t), , , and were low, but they were high for DVs for , , , , , (t), , , , (t), (t), and (t). Isolates were classified into three cluster groups Ia, Ib, and II based on reaction patterns to DVs and LTH.