| Rice blast caused by Magnaporthe oryzae is one of the three most destructive diseases in rice production in the world,which seriously damages the yield and quality of rice and has become the main obstacle to high and stable yield of rice.There is variety specialization and pathogen pathogenicity differentiation in this disease.It is the most economical and effective control method to breed resistant variety and utilize resistance variety.However,most resistant cultivars generally lose their resistance within 3 ～ 5 years of extension,and the variability of their pathogens is the fundamental reason for the loss of resistance.Therefore,insight into pathogenicity and dynamic change of pathogens is the basis of breeding resistant varieties and safe distribution of varieties.In order to systematically study the pathogenicity differentiation,genetic structure and resistance of rice blast fungus in Jiangxi Province.In this study,1161 strains of Magnaporthe oryzae isolated from different rice-planted areas in Jiangxi Province from 2006～2018 were tested.7 Chinese differential hosts were used to determine the physiology race of strains for test,30 monogenic lines of resistance to rice blast were used to determine the pathogenicity and avirulence genetypes of Magnaporthe oryzae.The genetic diversity of Magnaporthe oryzae population based on virulence-related gene sequences in five different ecotypes area in Jiangxi Province was analyzed.The mechanism of resistance loss was study by monitoring the resistace of ten super rice varieties planted in Jiangxi Province.And the transcriptome differences of Pi-zt was inoculated by different Magnaporthe oryzae.The main findings are as follows:1.The rice blast fungal strains from Jiangxi Provine were divided into 49 physiology races belonging to 7 groups,of which ZA,ZB and ZC groups were the dominant populations,ZB13 was the dominant race with the frequency of occurrence of 18.00 %.The strains of Jiangxi province were mainly strong virulence.In addition,they behaved a periodicity of 3 to 5 years in terms of dominance and virulence.Their pathogenic types were relatively abundant and exhibited year’s difference.The year’s percentage of rice blast strain’s pathogenic types was 82.79 % to 98.21 %,and the year’s percentage of dominant pathogenic type was 3.57 % to 5.77 %.The number of avirulent genes of Magnaporthe oryzae in Jiangxi Province was found to be 24 to 29 in 2006～2018,and the avirulent genes of Avr-Pizt,Avr-Piz5,Avr-Pik,and Avr-Pik(C)occurred more frequently in Jiangxi.2.189 strains of rice blast fungus isolated from rice-growing fields in five areas of Jiangxi Province,China,were amplified with 16 pairs of virulence gene-specific primers.Fifteen pairs were able to amplify their target bands.The percentage of polymorphic sites was as high as 93.75%,and the frequency of amplification varied greatly.Cluster analysis classified the 189 strains,represented by 108 different haplotypes,into 21 genetic lineages at a genetic similarity level of 0.80.JXH16 was the dominant haplotype.The 21 genetic lineages included 1 dominant,2 subdominant,12 secondary,and 6 minor lineages.At the population level,rich genetic diversity was observed among the 189 strains from different geographic regions(H = 0.2890;I = 0.4398).At a genetic distance of 0.02,the five populations were clustered into three groups that were unrelated to geographical distribution.A certain level of genetic differentiation was found to exist within each blast fungus population(HT = 0.2842).Within-population genetic diversity was higher than that among populations(Hs = 0.2210;Dst = 0.0632),with 77.75% of the total genetic variation originates within populations(Gst = 0.2225).Some within-population gene flow were detected(Nm = 1.7473).3.The disease index of 10 super rice varieties exhibited an increasing trend,and the resistance level decreased in four consecutive years.We focused on the analysis of Ganxin203 and Zhuliangyou 02,which were cultivated for 4 years,and the number of dominant race and the average virulence frequency of strains from the two varietes increased every year for four consecutive years.And we tested the avirulence gene in the strains from the two varieties,the result indicated that the frequency of the avirulent genes gradually decreased in the two varieties for four years.Compared with the results of the resistance gene test of the two varieties,the number of avirulencee genes that corresponded to resistance genes of Zhuliangyou 02 was higher than that of Ganxin 203,and these avirulence genes also had higher frequency.It was evident that the main cause of resistance loss of the super rice varieties was the selection of a dominant physiological species of the rice blast,while the occurrence frequency of the avirulence genes that induced the occurrence of resistance with the resistance genes of the rice variety was decreasing every year.4.The samples were sequenced using Illumina RNA-seq sequencing platform for high-throughput transcriptome sequencing.The clean reads were selected to map the reference sequences of rice genome(NCBI GCA＿001623365).The results showed that85.10% ～ 87.49% clean reads could be matched to unique genome locus.The gene expression level was calculated using RPKM method.The false discovery rate≤0.001 and the absolute value of | log2 Ratio |≥1 were used as the threshold to judge the significance of gene expression differences.Finally,the functions and pathways of differentially expressed genes(DEGs)were annotated by comparing them with the Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG).According to the top5 GO classification,the main functions included catalytic activity,metabolic processes,binding,cellular processes and stress response.Among them,50 DEGs could be classified into the KEGG pathway,including 46 up-regulated DEGs and 4 down-regulated DEG.These pathways were associated with amino acid biosynthesis,carbon metabolism,plant hormone signaling,RNA degradation,organic acid metabolism,glycosaminoglycan degradation,Olefin degradation,and Carotenoid biosynthesis.It was found that the resistance of rice variety Pi-zt to rice blast was a complex process,which is regulated by many cross pathways,including metabolic pathway,enzyme activity regulation,environmental information processing and plant hormone resistance signal pathway,etc.It is closely related to rice resistance to rie blast for DEG,MH11G0500600(transposable enzyme family protein gene)and MH04G0435600(pectin methyl esterase gene)). |
