Race diversity and virulence complexity of Phytophthora infestans in Nepal

A total of 251 Phytophthora infestans isolates collected during 1999-2000 potato growing seasons from nine potato growing areas of Nepal were tested for virulence using a set of eleven potato differentials. The virulence test revealed the presence of 30 races with the most frequent being 4.11, 4 and 11, Twenty-nine percent of isolates belonged to simple races having none to one virulence factor, whereas 71% had complex virulence factors governed by 2 to 7 genes. Gleason and Shannon indices of 5.24 and 2.59, respectively, showed a moderate level of diversity in Nepalese P. infestans populations. Shannon indices comparison among regional populations revealed significant differences (t-test, P<0.001) in the diversity. The population from hills were the most diverse followed by terai and the high hill populations. The virulence complexities were minimal in Nepalese populations. The implications of these findings in association with the potato cultivation system in Nepal are discussed.