| Totally 72 strains consisted of 17 representations of XOO and their mono-cell clones from China, Philippines and Japan, were inoculated on the flag leaf of 16 near-isogenic rice lines with IR24 as recurrent parent, at the flag leaf stage, to compare the difference of their virulence. The result indicated that the average percentage of the strains showed susceptibility (S) on 16 lines from China and Philippines was about 40-42%, while Japan was 31.2%, there was abate 10% higher of China and Philippines than Japan. IRBB5 (Xa5), Asominori (Xa17) and IRBB21 (Xa21) were all highly resistant to tested strains from the three countries, so did IRBB7 (Xa7) to China and Japan (the percentage of strains resisted >97%), but 30% strains from Philippines could overcome the resistance of IRBB7 (Xa7) . The percentage of strains resisted by IRBB13 (Xal3) , IRBB4 (Xa4) and XM6(Xa20) from China was over 90%, but 45% strains of Japan and 35% of Philippines could overcome their resistance. Most strains of Japan and Philippines were avirulent on IRBB3 (Xa3), except China. These results could be useful to the intercommunion of resistant resources among the three countries.It was determined by SAS software that the ratio of the length of lesion on diseased leaf (RLLDL) caused by 72 strains on 18 varieties (Jinggang30, Tetep and 16 near-isogenic lines). According the result , 18 varieties were plotted out 6 groups, which were high resistance(HR) , resistance(R) , medium resistance(MR) , medium susceptibility(MS) , susceptibility(S) and high susceptibility(HS). Based on the 6 groups, two groups of differentials were picked out.The first group consisted of 6 varieties of Fengjing (Xal8) , IRBB14 (Xal4) , IRBB3(Xa3) , IRBB4(Xa4) , Javal4(Xal,3,12) and IRBB5(Xa5) , was adapted to distinguishing the virulence of the nature group of XOO. Based on it, 72 strains were classified into 10 pathogen groups with 18 reaction types, such as 0,1, 2, 3, 4, 6, 7, 8, 9, 10, in which the virulence of group 0-6 changed from leak to strong in quantity diversification, while among and in the group 7-10 it changed as cross interaction in quality diversification. The ratio of these strains was accounted for 34.4% in tested strains.The another group consisted of 10 varieties of Fengjing (Xal8) , XM5 (Xal9) , IRBB14(Xal4) , IRBB3(Xa3),XM6(Xa20),IRBB4(Xa4),M41(Xa15),Javal4(Xa1,3,12),IRBB5(Xa5)andAsominori(Xal 7), was adapted to identifying and monitoring difference races of the virulence of strains. Based on it 72 strains were fallen into 16 groups with 29 reaction types, such as 0, 1 ,2, 3, 4, 5, 6, 7, 10, 12, 13, 14, 15, 16, 17and 18, in which the virulence of group 0-10 changed from leak to strong in quantity diversification, while among and in the group 11-18 it changed as cross interaction in quality diversification. The ratio of these strains was accounted for 45.9% in tested strains. The pathogenicity of 64 strains of XOO was tested on 16 iso-genitic rice lines which isolated from Hunan, Guangdong, Yunnan and Hubei provinces. According to the percentage of strains resisted by iso- genetic rice lines(PSRBIG) , 16 of iso- genetic rice lines were plotted out 6 groups which were HR, R, MR, MS, S and HS. IRBB7(Xa7) and M41(Xal5) were belong to HR group, their percentage of resisted strains was over of 85% and lesion on leaf was less of 16 %; IRBB5(Xa5) >. Asominori (Xal7) and IRBB21(Xa21)were belong to R group, their percentage of resisted strains was 65-85% and lesion on leaf was 16-25%;IRBB2(Xa2), IRBB4(Xa4) and IRBB13(Xal3) were belong to MR group, their percentage of resisted strains was 45-65% and lesion on leaf was 25-35%; XM5(Xal9), IRBBl(Xal), IRBB14(Xal4), XM6(Xa20) were belong to MS group, their percentage of resisted strains was 40-45 % and lesion on leaf was 25-35%, Fenggjin(Xal8) was belong to HS group, their percentage of resisted strains was less than 20% and lesion on leaf was over than 65 %.In order to understand the pathogenicity of XOO strains from central-south rice growing region on pile- genetic lines, it was studied that the interaction with 64 strains of XOO on 6 pile- genetic lines introduced into from IRRI (International Rice Research institute).The results showed that : the percentage of resisted strains of varieties with Xa4 combined with Xal3(43.8%) was similar to that with single Xa4(45.3%) and single Xal3(46.9%) ,while It was notably declined compared with that of single Xal5(85.9%) and single Xa21(65.6%) when gene Xal5 combined with Xa21(59.4%) ,but it was enhanced remarkably compared with that of single Xal(42.2%) and single Xa2(45.3%) when gene piled with Xal,2,12(75%) .The resistant ability of varieties combined with genes of Xa4, 7, ofXa4> 5> 21, ofXa4% 5, 19> 21andofXa5, 13> 21. was highly reinforced , their percentage of resisted strains reached 100% to 64 strains.Thus it can be seen that cumulated genes may or may not increase resistance of the variety. Our result showed that the varieties of H-36, H-38, H-39 and H-41 piled with genes of Xa4> 5> 7> 21 had wonderful resistance to strains of central-south rice growing area, which can be used as resistant parents.The pathogenicity of 64 strains of Xoo was tested on 6 differential varieties of Fengjin(Xal8) , IRBB14(Xal4) , IRBB3(Xa3), IRBB4(Xa4) , Javal4 (Xal, 3, 12) , IRBB5(Xa5) which was classified into 10 groups and 14 reaction types. The virulence of group Ck K 2^ 3^ 4^ 5> 6 changed from weak to strong in a quantity diversification , which was 50.1% of tested strains ; The virulence of group 7 ^ 8^ 9> 10 changed as cross interaction in quality diversification, which was 49.9%.Whereas the proportion of group 0 , 4> 7, 5 was 18.8%, 17.2%, 15.6% and 12.6% in file and the rest was under 8%, the group 4 and 7 were the major populate groups in central-south rice growing region . So it was suggested to be used as tested strains that selected from groups of 4 and 7 when identifying disease resistance.of varieties.In our test that the percentage of strains overcame the resistance of IRBB4(Xa4) was 54.7%, which was very different from beforetime. While the percentage of strains can overcome piled genetic of Xa4, 5 s 15 s 7, 21 was under 25% , it was advised to increase the force of using these genes andpiled- genetic in future.It was Compared that the virulence of the model strains that 5 of strains from China, 9 from Philippine and 3 from Japan and their mono-cell-clones of Xanthomonas oryzae pv. Oryza tested on the Near Iso-genetic Lines consisting of 10 varieties of fengjin(Xal8) , XM5(Xal9) > IRBB14(Xal4) , IRBB3(Xa3) , XM6(Xa20) > IRBB4(Xa4) , M41(Xal5) , Javal4(Xal4) > IRBB5(Xa5) , Asominori(Xal7).The result showed that there was only 11.8% of tested strains which the virulence of model strains was equal to their mono-cell-clones and 88.2% of them their virulence was different from their mono-cell-clones in 17 of tested groups. This sufficiently indicated that the strains isolated by the common method must be a compound with different virulent cells. The virulence of 7 groups of mono-cell-clones was compared with their "re-isolated mono-cell-clones". 42.9% of tested groups which the virulence of parent mono-cell-clones was equal to their "re-isolated mono-cell-clones" and 57.1% of them was different. Although It suggested that the method by mono-cell-clones isolation could discriminate the different virulent cells effectively, only once re-mono-cell-clones isolated couldn't dissociate the different mono-cell-clones sufficiently, which should be carried through more times in order to maintain the virulent stability of the strains.Because of the strains isolated by common method were made up of different virulent cells, the molecular enlarged segment would be tangled and couldn't be repeated when the those kinds of strains were tested by molecular biology technology. Therefore it was very necessarily to using the high simplex mono-cell-clones as tested material when pursuing molecular marker technology to distinguish different virulent races.IS-PCR, Rep-PCR and 6 primers were used to analyze genetic diversity in a population of 114 strains of Xanthomonas oryzae pv. oryzae. The result indicated the distinguishing ability of IS-PCR was higher than Rep-PCR. The distinguishing ability of J3 was first, IS1112 the second and IS113 third among the 6 primers.According to the band number of amplified fragments with IS-PCR and Rep-PCR, the first was Philippine's strains, the second was Chinese's and the third was Japan's.The strains with different virulence could be classified into a same cluster and the strains with same virulence could be classified into different clusters according to the UPGMA cluster analysis on bands , which indicated that there was no distinct relationship between the clusters with virulence of strains by IS-PCR and Rep-PCR with 6 tested primers.Whereas various mono-cell-clones from the same mother strains could be distinguished to different clusters, which further proved there must be some genetic diversity among them. Therefore it was very necessarily to using the high simplex mono-cell-clones as tested material when pursuing molecular marker technology to distinguish different virulent races.
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