Analysis Of Genetic Diversity Of Magnaporthe Oryzae Isolates From Zhejiang Province,Over The Past Thirty Years Based On Avirulence Gene

Rice blast, which is caused by Magnaporthe oryzae, is one of the major diseases of rice. The occurrence and prevalence of rice blast may significantly reduce the yield and quality of rice. Large-scale spread of rice blast has been reported in recent years, causing considerable economic loss. The screening and selection of resistant varieties is regarded as the most effective solution to rice blast. Genetic variation in M. oryzae isolates and continuous planting of rice varieties with the same or similar resistance genes may result in the enrichment of virulent strains and hence population succession. Enriched pathogenic strains enhance the susceptibility of rice varieties to disease, accelerating the loss of rice blast resistance. By detecting genetic variations in M. oryzae isolates, we can not only elucidate the complexity of genetic diversity but also predict the succession of field populations, which is closely related to the loss of rice blast resistance.So far, the commonly used methods on research of the genetic diversity are molecular marker techniques, such as Restriction Fragment Length Polymorphism (RFLP), Random Amplified Polymorphic DNA (RAPD), Sequenced Characterized Amplified Region (SCAR), Simple Sequence Repeat (SSR), repetitive element-based Polymerase Chain Reaction (rep-PCR), Amplified Fragment Length Polymorphism (AFLP), Retrotransposon-Microsatellite Amplified Polymorphism (REMAP). Until now, no apparent correlation was found between the clustering results deduced by the polymorphism of molecular markers and the pathotypes of M. grisea. The specific interaction between rice and M. grisea follows the gene-for-gene hypothesis, and the cognate genes in M. grisea were called AVR genes. During the interaction between M. grisea and its host, AVR genes always exhibit the characterization of instability. The mutation of the region of AVR genes usually result in the loss of the resistant of rice. Understanding of the mutation mechanism of AVR gene is important for breeding resistant varieties to control rice blast, at the same time, the variation of AVR gene is appropriate for the study of genetic diversity of M. grisea.In this paper, ITS (Internal Transcribed Spacer), SSR (Simple Sequence Repeat) A VR gene were applied to detect the genetic diversity of M. oryzae strains isolated from11different areas in Zhejiang Province, from1978to2011. The following is a brief introduction of the relevant research, the progress and the significance of these studies:1. The results of ITS research show that ITS-5.8S rDNA region had207mutant sites and8independent haplotypes. The phylogenetic tree of the8haplotypes can be divided into two major branches. The average haplotypic diversity (Hd) was0.346and average nucleotide diversity (Pi) was1.945%. Among the populations studied, the Li Shui population had the highest genetic diversity, the Jin Hua and Zhou Shan population had the lowest genetic diversity. Analysis of molecular variance revealed genetic variations were mostly confined within the populations. Among the populations had a high degree of gene flow, and genetic differentiation in the M. oryzae population was not consistent with a simple model of isolation based on distance.2. SSR results show that28pairs of SSR primers can amplified171allele in total, the allele number of each pair of primers amplified were2to24, the average diversity index was0.534and the average polymorphism information content was0.494. The Li Shui, Hang Zhou and1990populations had the highest genetic diversity, the Zhou Shan and1978populations had the lowest genetic diversity. The strains isolate from indica rice had the higher genetic diversity than strains isolate fromjaponica rice.3. The major types of mutation of AVR gene in M. oryzae isolate from Zhejiang Province was deletion and insertion, most of strains contain the ACE1and AvrPiz-t, only a small number of strains containing the AVR-Pia, AVR-Pii, and PWL4, the AVR1-CO39and PWL1loci of all strains were missing. The utilization of AVR gene to study the genetic diversity of M. oryzae was feasible, and it had a higher polymorphism results. The Li Shui population had the highest genetic diversity and the Zhou Shan population had the lowest genetic diversity. Gene expansion out rate of Tai Zhou population was the highest and the Wen Zhou population was the lowest. The strains isolated in20th century had the highest genetic diversity and strains isolated in1980s had the lowest genetic diversity. The2001and1994populations had the highest genetic diversity and the2003and2008populations had the lowest genetic diversity. The strains isolate from indica rice had the higher genetic diversity than strains isolate from japonica rice. 4. The A VR gene, ITS and SSR technology all resulting in the consistent results of genetic structure diversity of M. oryzae isolated from Zhejiang Province. Such as the genetic structure of M. oryzae isolated from different areas was quite different, of which the Li Shui population had the highest genetic diversity and the Zhou Shan population had the lowest genetic diversity. Higher genetic diversity of M. oryzae isolated in different years, the genetic structure of2002,2003,2008and2011were similar. The genetic structure of M. oryzae isolated from different rice types was quite different, a part of strains isolated from indica and japonica had the similarity genetic structure.