Studies On The Pathogenicity Of Magnaporthe Oryzae In Three Different Rice Growing Regions And Their Interactions To Rice Varieties

Rice blast, occurred in all rice growing regions (RGR) in China, is an important fungal disease ofrice and caused significant yield losses. The use of resistant rice varieties is one of the most economicaland effective method for controlling rice blast. While, the resistance of rice varieties decreases or losesafter large-scale planting for three to five years. Investigation of physiological races (PR) of rice blastfungus, Managrothe oryzae(M.oryzae), and rice varieties’ resistance to blast will provide withsignificance guidance for reasonable layout of the resistant varieties.In this study, the infected rice blast samples were collected from Heilongjiang, Zhejiang andGuangxi rice growing regions where great different in geographical environment and climate conditions,and144M. oryzae isolates were isolated. The PR of89isolates of them was identified. The resultsindicated that the89isolates could be divided into35PRs and distribute seven groups. The occurrencefrequency of group ZB, ZA, ZC and ZE was50.56%,22.47%,12.36%and7.86%, respectively, andoccurrence frequency of ZD, ZF and ZG group’s were the same of2.25%.24isolates what come fromHeilongjiang RGR were identified, the predominant races were ZB1and ZE1with the same occurrencefrequency of12.5%.47isolates of Zhejiang RGR were identified, the predominant races were ZB15andZB9with the frequency of19.15%and10.64%, respectively.18isolates of Guangxi RGR wereidentified, the races of ZA11、ZA7and ZA15were the dominant populations and their occurrencefrequency were16.67%，11.11%and11.11%, respectively. The genetic diversity of144isolates of M.oryzae which isolated from three RGR was analyzed. According to the UPGMAA (unweighted pairgroup method with arithmetic average), all isolates can be classified into seven genetic genealogies at0.83level of the genetic similarity. The genealogy I was the predominant with rates of74.31%. Isolatesof Heilongjiang and Zhejiang RGR can be divided into multiple genealogy and existed specific lineages,while all isolates from Guangxi RGR belong to genealogy I.In recent years, rice blast was occurred quite seriously to the varieties (combinations) of MR219(from Malaysia，represent for south rice regions), Zhongzheyou1(ZZY1, from Zhejiang) and Kongyu131(KY131, from Heilongjiang) in.their main growing regions. The resistance of the four rice varieties(combinations) of MR219, ZZY1, Zhongzheyou8(ZZY8, sib line of ZZY1which show resistance toblast and also from Zhejiang) and KY131to56isolates from the three RGR of blast fungi was tested inthis study. The results showed that the resistant rate of KY131to M. oryzae strains of Guangxi RGRreached69.57%, while the resistant rate to Heilongjiang strains was only10.53%. The resistant rate toHeilongjiang strains of ZZY1reached73.68%, while only42.86%and30.43%of resistance rate to M.oryzae strains of Zhejiang and Guangxi. The resistance rate of ZZY8to M. oryzae strains of the threeRGR is almost equal, between57%to61%, the resistance rate of ZZY8to Zhejiang and Guangxistrains was significantly higher than that of ZZY1. The resistance rate of MR219to M. oryzae strains ofHeilongjiang reached73.68%, while the resistance rate was only39.13%and21.43%to Guangxi andZhejiang strains, respectively.The rice varieties’(combinations’) resistance to local strains of rice blast pathogens islower than that of to other RGR, this could explain that why rice blast of these varieties (combinations)occurred so serious in local growing regions in recent years. On the other hand, the resistance of thesame rice variety (combination) to the isolates of different RGR existed obvious differences. Except forthe direct relationship with the pathogenicity of M. oryzae strains, the occurrence of abovephenomenons may also connect with long terms host-pathogen interaction and directional selection.Studied on reactions of the representative rice blast isolates from three RGRs to illuminationtreatment. Under different illumination treatment, illumination time made no obviously effect on riceblast fungus growing.