Genetic Diversity In Magnaporthe Grisea In Jiangsu Province

One thousand thirty-two monoconidial isolates were obtained from rice blast specimen collected from Jiangsu province during 1 980--- 1996 were classified into 8 groups and 22 races by assessed with 7 Chinese differential rice cultivars. The predominant race was ZG1 in the duration, except in 1990 and 1991 was replaced by group ZA and group ZD , ZE respectively. The appearance frequency of race ZG1 was as high as 66.20% , followed by race ZF1 with an incidence of 8.02%. The frequency of the both races were stable among the most years monitored. Lower appearence frequency (3. l0挆8.30%) was detected in group ZA, ZB, ZC, ZD and ZE and fluctuated annually. The race composition were also dissimilar in different rice areas in Jiangsu Province. The most complex race composision was presented in Taihu area and Along the coast and Yangtze river area, where the rice blast disease occured severly and widespreadly, 16 and 12 races were identified in the both areas respectively. Relatively simple composition of races was in Lixiahe rice area and Hills rice area, where the disease incidence was lower, and only 6 and 5 races were identified respectively. Most rice cultivars in Jiangsu province were compatible with race ZG1, but few with group ZA, ZB, ZC, ZD and ZE. It was a possible explanation why the ZG1 was the predominant race in Jiangsu province and the race composition on a same cultivar might be dissimilar in different rice area showed that the composition of race was complex in the field. The results of this paper suggested that the 101 constitute of rice cultivars was one of nuin determination factors for race composition in the field, and the climate and cmp~ing sywtem might also affect the race evolution. Three hundred twenty-four monoconidial isoltes w~n obtained from rice blast specimen collected from 5 typical areas梂ujiang, Garayu, Tongzhou, Gaoyou and Yixing in Jiangsu province during 1997?999. The isolates were assessed with 7 Chinese differential cultivars and 13 Japonese culitvars which resistance genes have been determined. By inoculating on 7 Chinese differential cultivars, 21 races were identified, and ZG1 race was predominant with 57.80O/a~~~67.89% frequency. Race composition and variation were dissimilar in different areas, and closely related with rice cultlvars. By inoculating on 13 Japonese culitvars, above isolates were divided into 90 pathotypes. Which indicate that there wer pathotype diversity in Magnaporthe grisea in Jiangsu province. The pathotypcs were dissimilar in different areas and in different year, and as time goes on, this dissimilar was increased. The as~ssed results were also compared between on 7 Chinese differential cultivars and on 13 Japonese cultivars which resistance genes have been determined, which suggested that differentiating ability of Chinese differential varieties was low and was not suitble for practice. The analysis of virulence frequency indicated that the resistance genes Pi~ks, Pi-ta, Pi-ta2 and Pi-sh had lost resistance to Magnaporthe grisea of Jiangsu province. But the resistance genes P1-i, Pi-z?and Pi-b still had high resistance to Magnaporthe grisea in Jiangsu province and bad high use value in rice breeding as resistance resources. The ~valualion of resistance of 80 major cultivars and newly-bred cultivars in Jiangsu provkice showed that there were high resistance in Indica cultivars and hybrid rice. And the resistance i...