Identification Of Pathogenic Race And Genetic Diversity Of Xanthomonas Oryzae Pv. Oryzae In Hubei Province

Presently screening and planting resistant varieties is the most economic and effective approach to resist bacterial blight in rice production, whereas the prevalence of virulence differentiation and the continuous pathogenicity variation in the pathogen make great trouble for the breeding of resistant varieties. Therefore, in order to understand the bacterial virulence differentiation and population structure of of different regions, as well as perform rational distribution of resistant varieties, rotation and mutual exchanges,it makes great sense to undertake the studies of pathogenic bacteria races and genetic diversity, from which important forward-looking information derived would be necessary references for in-depth breeding strategy and continuous improvement of varietal resistance.In all,263 strains of Xoo used in this study were isolated from standard samples collected in 38 counties of Hubei Province. Identification of pathogenic races was performed on the 6 near-isogenic lines of rice, IRBB5 (Xa5), IRBB13 (Xa13), IRBB3 (Xa3), IRBB14 (Xa14), IRBB2 (Xa2) and IR24 (Xa18), each carrying a specific R gene. As is demonstrated in the results, the dominant pathogenic race in Hubei is R4, followed by the R5 & R3,R7 & R8 were not found, and the pathogen population constructure in one region differs from another. The dominant race is R4 in Wuhan, both in Xiaogan and Yichang the priority race is R4,R5,R9,Huanggang is dominated by R3 & R4.In Xianning the dominant race is R3 & R5,while R5,R2 & R4dominated Jingzhou and Xiangfan separately. Meanwhile, the race style also associates with rice property, the race type is the most abundant in medium rice, and Xoo on early rice is of lower toxicity, while the most severe toxic race R9 only exists in mid-season rice. In addition, we also compared the race composition of different infected plants in a single field and distinct leaf fragments of a single diseased plant, and found that the virulence differentiation commonly exists everywhere, which is of non-regularity and in a completely random state.On the basis of race identification, we also analysed the genetic diversity of 263 Xoo strains by means of Rep-PCR and IS-PCR.6 special primers ERIC,BOX,REP,J3,IS1112,IS1113 were selected for PCR amplification of 263 Xoo strains* genomic DNA.6 primers present 26,18,9,24,21,28 types of pattern separately. Fringed by bands similar rate of 70% between each other, using UPGMA 11 clusters (ERIC) were revealed among 263 strains, while 3 clusters (BOX),5 clusters (J3),7 clusters (IS1112) and 6 clusters (IS1113).It is thus clear that the optimum primer for genetic diversity analysis of bacterial leaf blight is ERIC in Hubei, followed by IS 1112 and IS 1113. Genetic clustering has certain relevence with geographic region, strains with close geographic origins are often close to each other in genetic distance. Obvious relevence was not found between race identification results and analysis of genetic diversity.In this study,we also mensurated the reproduction rate, lawn color and viscosity of 56 Xoo strains from Yichang. It is demonstrated that there is considerable variability in the growth rate of the 56 strains, even if among isolates from a single field and strains isolated from the same leaf. Most of the strains'growth rate reached peak value after 48h cultivation.YC1,YC31,YC35,YC38,YC45,YC51,YC56 these 7 strains grow faster than other strains and their OD600 peaked after 24h cultivation.However,6 other strains including YC5,YC14,YC19,YC36,YC40,YC49 shared obviously lower growth rates than other strains,and the OD600 could not peak even when they were cultivated for 72h. Growth rate of the strains did not associated remarkably with their pathotypes. Meanwhile, the lawn color and viscosity of the 56 strains could be classified in 6 forms, most of the strains fall into the form B, whereas form F occupies the least number of strains. Certain mutualities lies between the lawn color & viscosity of the strains and the virulence &the growth rate. Strains in A form often have stronger virulence, while strains in C form shared lower virulence and moderate growth rate. Those in D form are either more virulent or grow faster. Strains sharing appearence of E form usually less virulent, while those in F form often grow slowly. Strains of form B did not show evident relevence between the lawn color & viscosity of the strains and the virulence &the growth rate.