| Rice blast (Magnaporthe oryzae) is one of the devasting diseases on rice crops all over the world, causing severe reduction in the output and poor quality of rice. Breeding and planting resistance varieties are the most efficient and safe methods to control the disease but the the resistance in the field was frequently broken down due to the changes in the population virulence of the pathogen. So the monitoring of the changes in virulence of rice blast fungus is essential to the success of the deployment of reisistance varieties as well as the prideiction of the disease epidemic. In this research,638 isolates of M. oryzae were isolated in 2002-2009 from different varieties in different regions of Sichuan Province and inoculated onto 7 rice varieties to differentiate the virulence types of the fungus and trace their changes. Tetep has been broadly used as resistance donor in the hybrid rice breeding project in Sichuan and other regins of the world. To determine the efficiency of one of the reisitance gene derived from Tetep in Sichuan,220 isolates were inoculated to IRBL13 which has been validated to carry resistance allele of Pi-ta after the base sequence of the gene. The obtained results were as listed below:1. One method for virulence typing and nomenclature weas determined:the virulence to the varieties "Lijiang Xintuan Heigu" (LJH), "IR24", "Minghui 63"(MH63), "Duohui No.1 (DH1), "Chenghui 448"(CH448), "Niehui 99-14"(99-14) and "RHR-1" was respectively scored at 1,2,4,8,16,32 and 64. The total virulence score of a M. grisea isolate which was the sum of scores infecting individual vareieties then could be as the name of the virulence type, due to its correlation to a special virulence pattern to these 7 differentiating varieties.2. The 638 tested isolates were differentiated into 56 different virulence types. There were 24 virulnce types with the frequencies higher than 0.5% in 2002-2009. " Type15" compatible to LJH, IR24 and MH63, and "Type 127" compatible to all 7 varieties were the most dominant virulence types. Their frequencies in 2002-2009 were respectively 15.99% and 15.83%. "Type 19" and other 7 virulence types were not monitored in the period.3. Among the virulence types with the frequencies higher than 2.0%, the majority of the isolates virulent to DH1 were also virulent to MH63 whereas all of the the isolateds virulent to CH448,99-14 and RHR-1 were also virulent to MH63. The majority of the isolates virulent to CH448,99-14 or RHR-1 could also infecting IR24 and DH1. These results indicated the aquisition of the virulence in M. oryza impacted by the sequential large scale plantation and withdraw of IR24, MH63 and DH1.4. The virulence frequencies of the 638 tested isolates to IR24, MH63, DH1, CH448, 99-14 and RHR-1 were respectively 74.6%,79.5%,73.8%,37.0%,39.0% and 40.4%。5. Type 15 was most dominant virulence type in 2002,2003,2004 and 2007 whereas Type 127 had been the most dominant virulence type since 2005 except for the year 2007. The virulence frequencies to CH448,99-14 and RHR-1 had been also increased since 2005 with exception for 2007.6. Among the 3 IRBL lines supposed to carrying blast resistance gene Pi-ta, only IRBL 13 was validated to carry the resistance allele of which, the amio acid residual at 918 was alanine, the same as to that in "Tetep". IRBL 12 was validated to carry the resistance allele of which, the amio acid residual at 918 was serine, the same as to that in IRBL29.7. The virulence frequency of M. grisea to IRBL 13 had been higher than 86.36%, indicating the inefficiency of Pi-ta in Sichuan Since 2002. |
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