Studies On Virulence Differentiation And Genetic Diversity Of Xanthomonas Oryzae Pv.oryzicola Strains

By the pin prick method of inoculation, the interaction of 20 rice varieties and 40 strains of Xanthomonas oryzae pv. oryzicola(Xoo) were studied. According to resistance susceptibility and period of growth of these rice cultivars, Jingang30 Zhaiyeqing XM5 XM6 M41 were selected as differential host from 20 rice varieties and 40 strains were classified into seven pathotypes 0, I , II, III, IV, V , VI . Compared with the differential host from Zhejiang,Hunan and Guangdong, the differentials screened by this test could differentiate the quantity variation from weak to strong and the quality variation of cross interaction of virulence of these strainsThe pathogenicity of 75 isolates of Xanthomonas oryzae pv. oryzicola(Xoo) from the provinces of Hubei, Hunan, Jiangxi, Fujian was tested on 5 differential varieties of Jingang 30, zheyeqing,Xm5, Xm6 and M41. It was classified into seven pathotypes of 0, I, IK III, IV. V, VI with reaction patterns of RRRRR, SRRRR, SSRRR, SSSRR, SSSSR, SSRSR, SRSRR. The virulence of 0, I , IK III, IV represented as quantity variation from weak to strong and there was quality variation with cross interaction between V and VI. The proportion of 0, I , IK HI, IV, V, VI was 5.3%, 9.3%, 20%, 44%, 10.7%, 6.7%, 4% respectively. The result indicated that the predominant pathotype was III and IVin Fujian and Jianxi, the proportion of which was 88%, 50% in turn; II and III in Hubei, the proportion was 70%; no predominant pathotype in Hunan but the sum of proportion of II, III, IV was 55.6% comparing the pathogenicity of Xoc from four provinces.It was comparied on 5 differential varieties of Jingang30, Zhaiyeqing, XM5, XM6, M41 that the virulence of strain RHL1-2 (pathotype 0), RJ3-2 (pathotype II) , RJX3-2 (pathotypeIII) , RH2-2 (pathotypeIV) and their 39 mono-cell clones(MCC ). The result showed that virulent pattern of RHL1-2 and its MCC was pathotype 0; RJ3-2 and its MCC fell into pathotype 0; RJX3-2 fell into pathotype II ,one of its MCC represented pathotype I , three did pathotype II, five did pathotypelll; RJX3-2 fell into II, four of its MCC represented 0, one did I, two did II, one did III and one did D. There was significant difference among the virulence of RJX3-2, RH2-2 and their MCC on Jingang30, Zhaiyeqing and XM5 tested By SSR (Duncan). The results suggested that the original strains isolated from leaf of rice should be made up of different virulent cells. The virulent variation of mother strains was owed to the changeover of composition of strains.As it was different that the survival rate of different virulent MCC in mother strains after a period of preservation in refrigerator.Rep-PCR was used to analyze the genetic diversity in a population of Xanthomonoas oryzae pv.oryzicola (Xoo) isolated from 4 provinces. Genomic DNA from 35 strains was amplified with two specific primers (BOX and ERIC). 14 bands and 10 patterns of DNA fringer-prints amplified by BOX-PCR. And 19 bands and 17 patterns were got by ERIC-PCR. The range of genetic diversity value was 0.63-1.00 with BOX-PCR and 0.86-1.00 with ERIC-PCR based on pathotypes , which indicated the primer ERIC was better than BOX in estimating the genetic diversity of Xoo. There was no correlation between the pathotypes , geographic source and clusters based on patterns of DNA fringer-prints.Genomic DNA from 4 mother strains and their 36 mono-cell clones(MCC ) was obtained by BOX-PCR and ERIC-PCR. The result showed that there was genetic difference in MCC from the same mother strain or the different strains, but the difference had no correlation with pathogenicity of MCC . The level of difference in MCC from RJX3-2 strain was 27.3% , which proved that the mother strain was composed of different MCC.