| China is the biggest potato-growing country in the word. With the implementing of the potato staple food strategy, the requirement of the potato yield and quality will be higher and higher. However, due to global warming, potato brown rot breaks out more and more frequently worldwide, and the popular area is more and more widely. But the detection and inspection of potato brown rot is still relatively defective in our country, the systemic investigation and identification of Ralstonia solanacearum is necessary.This study systematically collected natural suspected potatoes from 54 sites of 21 provinces (municipalities) in four potato major agro-ecological zones. By dilution streak method and specific primers 759/760, we isolated 123 R. solanacearum isolates from 24 of 54 sites from 11 of 21 provinces, even from Yakeshi, Inner Mongolia. It is obvious that brown rot is more and more serious in our country, especially in Central Double-cropping and Southwest Mixed-cropping zones. What’s more, it has grim trend to move to the north.By Biovar and Phylotype classification schemes,91% of 123 isolates belonged to race 3 biovar 2 (R3Bv2), phylotype IIB sequevar 1 (IIB/1), which widely distributed in four potato major agro-ecological zones. R3Bv2 isolates were the major pathogenic bacteria endangering potatoes in our country. The other isolates belonged to biovar 3, phylotype I, sequevar 13,16, isolated from potato in China for the first time,17,18 or 14M, a new sequvar, which has the nearest genetic distance with sequevar 14 strains of Pss81 and Zo4.Phylogeographic analysis of R3Bv2 strains isolated from different place can roughly speculate the routes of pathogen dissemination. Phylogenetic tree, constructed using multilocus sequence analysis (Multilocus Sequence Analysis, MLSA) with 37 representative R3Bv2 isolates, was divided into two groups:one group included 34 isolates from four potato major agro-ecological zones, and the other included only 3 isolates isolated from the Central Double-cropping. And what can predicte is that R3Bv2 strains were introduced in our country along a major route, and the Central Double-cropping zone may have other importing routes.To evaluate the pathogenicity of R3Bv2 strains to potato, three potato materials C9, W5337.4X and CT7-6 were inoculated with 34 representative isolates at low temperature of 20 ℃. It was found that only R3Bv2 isolates had strong or moderate virulence, and the other isolates just without or with weekly virulence, which showed that the R3Bv2 strains have cool adaptation. Howerver, the pathogenicity of different R3Bv2 strains were significant difference. For further studying temperature’s influence to virulence, C9 were inoclutaed with 9 isolates, representing different virulence types, at 28 ℃ and 20 ℃. The results showed that pathegenisity was influenced significantly by temperature, and differernt strains were affected significantly different. The analysis of pathogenic process showed that the progress of plant and pathogen interaction was prolonged, which incicated that there might have some virulen factor, regulated by temperature. So the strains, whose virulence affected by temperature differently, could be used for further exploring the virulence factors, regulated by temperature.In summary, a systematic survey of potato brown rot, by isolated and identified its pathogens, was conducted, which predicted that the major R. solanacearum was R3Bv2 in our country. The pathogenicity and genetic diversity of R3Bv2 strains were studied and summarized, as well. These new findings may provide important clues for prevention and treatment of potato brown rot, and a certain reference value for bacterial wilt resistance breeding. |
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