Distribution of Magnaporthe grisea Population and Virulence of Predominant Race in Jiangsu Province,China

Three hundred and forty-two mono-conidial isolates were obtained from rice blast specimens collected from five typical areas in Jiangsu Province during 2000-2002. The isolates could be classified into seven groups, thirty races when assessed with seven Chinese differential rice cultivars. The race ZG1 was predominant one of Magnaporthe grisea with a frequency of 65.00% in 2000, 56.90% in 2001 and 60.38% in 2002; the races ZB and ZC groups were also important in Jiangsu Province. By inoculating 130 ZG1 race isolates on thirteen Japanese cultivars with known resistance genes, forty-two pathotypes were found. Among them, 30.77% of ZG1 race isolates had virulence to rice cultivars Shin 2(Pita-ks, Pi-sh), K1(Pi-ta), Pi 4(Pi-ta2, Pi-sh), being the predominant pathotype, indicating the resistances of cultivars Shin 2 (Pita-ks, Pi-sh), K1(Pi-ta), Pi 4(Pi-ta2, Pi-sh) had lost the resistance in Jiangsu Province. Rice cultivar K3(Pi-kh) was highly resistant to Magnaporthe grisea with 100% resistance frequency, and resistant to the two single isolates, 2003-184(ZC5) and 2003-14-1(ZG1), however, it was infected by a mixture of the two isolates. It was suggested that the change in virulence stemmed from the interaction of different pathotype isolates was one of the reasons that made variety lose its resistance.