Pathotypes of Pyricularia grisea in rice fields of central and southern China

Blast, caused by the fungal pathogen Pyricularia grisea, is the most devast ating disease of rice worldwide. Knowledge of the pathotype composition of the pathogen in rice fields is essential for rational deployment of resista nce genes in rice breeding programs. In this study, we assayed the pathotyp es of the pathogen populations using samples recently collected from 13 maj or rice-growing provinces of central and southern China. In all, 792 single spore isolates were tested for pathogenicity reactions using 13 host diffe rentials consisting of six indica and seven japonica near-isogenic lines (N ILs). The compositions of the pathogen populations were complex; 48 pathoty pes were identified with the indica NILs, 82 pathotypes were detected with the japonica NILs, and a total of 344 pathotypes were identified with both indica and japonica NILs. There were large differences in distribution of t he pathotypes among the different rice-growing areas. Even neighbor provinc es seemed to differ sharply in types and frequencies of the most prevalent pathotypes. There was also a large difference in the frequencies of the iso lates producing compatible reactions on the NILs, indicating the difference in frequencies of avirulence genes in the pathogen populations. The data p rovided very useful information for formulating strategies for improving bl ast resistance in rice breeding programs.