| Rice blast, caused by the fungal pathogen Magnaporthe oryzae, is the most economically important disease of rice in Hubei Province, where there are3×105hm2rice-growing fields. Although cultivars with resistance to rice blast have been released in Hubei, they had not been efficiently explored in the Hubei rice breeding programs. The major reason for the low efficiency is that the resistance is easily overcomed by the arisen pathogen lately. In order to provide scientific information to allow the formulation of viable strategies for blast resistance breeding programs in Hubei Province and to efficiently and durably control the disease, the study on current information on the pathotype spectrum of Magnaporhthe grisea population in the rice fields of Hubei Province, on evaluating performance of rice blast resistance genes, and identifing new gene by using various rice varieties, would be made in the dissertation.500single spore isolates in the rice-growing fields of Yuan'an in Hubei Province where rice blast seriously occurs in some years.500isolates were pathotyped against two sets of host differentials:Chinese host differentials and monogenic lines (MLs).72pathotypes with the nine host differentials which carried known resistance genes for blast resistance of the rice blast fungus Magnaporthe oryzae were observed, while7race groups53pathotypes were observed out of the same single spore isolates with Chinese host differentials which consists of three indica cultivars and four japonica cultivars. The spatial and temporal subpopulation pathotype structures of the fungus were also analyzed and the result revealed that there was no obvious change of the population among different years, and the prevalent pathotype hold the line. At the same time, DNA fingerprints hapotypes were determined. DNA fingerprints were separated into14lineages at73%genetic similarity level. And among the lineage, none of the most prevalent linelage was found. The population genetic structures of Magnaporthe oryzae were not distinctly different in different years. The assay also showed that there weren't obvious and simple relationships between pathotypes and fingerprint groups. The gene Pi-kh had low susceptible frequency while resisting the rice blast fungus. The blast resistant gene Pi-kh can be well explored in blast resistance breeding programs in Hubei province.In order to evaluate performance of rice blast resistance genes in Hubei province,20monogenetic lines (MLs) derived from LTH were inoculated by nature in Jinziba and Lianghekou in Enshi district, Yuan'an in Yichang district and Chongyang district in Hubei Province, where blast occurs frequently and seriously in several years. The result revealed that genes Pi-kh, Pi-9, Pi-20and Pi-z5were incompatible to leaf blast while Pi-a, Pi-t, Pi-ta, Pi-z1,Pi-12(t) were compatible. Genes Pi-kp, Pi-kh,Pi-5(t), Pi-9and Pi were highly resistant to panicle blast while Pi-t, Pi-ta, Pi-zt, Pi-12(t, Pi-z were not resistant. Overall, there were genes Pi-kh, Pi-9and Pi-z5which had good resistance to rice blast including leaf blast and panicle blast can be used as rice blast resistance genes in Hubei rice breeding program, while it should be careful when the genes Pi-t, Pi-ta, Pi-z', Pi-12(t were used as resistance genes in Hubei.Assay for resistance of600rice varieties(lines) to rice blast disease was accomplished using22differential isolates of Magnaporthe oryzae. Based on the result, clustering analysis and genotype postulation were completed by unweighted pair group method with arithmetic mean (UPGMA). Resistance test data showed that significant diversity of resistance spectrum to differential isolates was found among the total of252rice varieties(lines).These varieties(lines) were classified into15groups according to the reaction patterns of resistance or susceptibility to differential isolates. Tested varieties(lines) belonging to different groups displayed distinct variation for reaction patterns and resistance frequncy. Genotype postulation indicated that14Pi-genes were involved in70of252varieties(lines). Another181varieties harbored none of the tested Pi-genes, however, they all carried other Pi-genes. The result from clustering analysis was not corresponding to those from genotype postulation simply. Ten varieties(lines), such as Zhenke and Mowanggu, were able to be candidate materials for field resistance evalution.A doubled haploid (DH) segregation population, which was composed of96different varieties, derived from cross between Mowanggu, an famous resistance parent to rice blast from Yun'nan Province, and E'wan8, a susceptible parent from Hubei Province, was used to analyse quantitative trait locus (QTL) for resistance to rice blast fungal pathogen Magnaporthe oryzae. The graphical genotypes was investigated using120simple sequence repeat (SSR) markers distributed on the whole rice genome chromosomes.5isolates were screened among22isolates of Magnaporthe oryzae, which could create insusceptible/susceptible reaction on Muwanggu/E'wan8, respectively. Resistance to rice blast of the DH was monitored using the5isolates by injecting the conidial suspension into the DH lines. QTLs analysis using phenotype and molecular markers was performed in the DH segregation population through composite interval mapping with MAPMAKER/Exp3.0.3QTLs were found to have linkgage with SSR marker RM541on chromosome6with variance explained between7.7%-15.2%. The3resistance QTLs were all donated by Mowanggu.
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