Study On Physiological Specialization And Identification Of Pathotype Of Ralstonia Solanacearum From Tobacco In Chongqing

Tobacco bacterial wilt, which is a kind of bacteria disease caused by Ralstonia solanacearum .E.F Smith and greatly affect tobacco product quality, is one of the most destructive disease on the threatening tobacco crop worldwild and is hard to control. So far using disease-resistant varieties is the most effective way to control this disease. Biovar, the physiological race and pathotype of R. solanacearum from native tobacco should be studied for breeding of disease-resistant tobacco varieties. Identification of Biovar, physiological race and pathotype of R. solanacearum from native tobacco is the precondition and foundation in screening of resist source preparation, breeding and spreading of disease-resistant varieties. In the study several bacteria isolates were separated from typical disease samples in tobacco planting area in Chongqing, and then, these isolates were cultured on media, tested in flagellum pigmentation, morphologic observation and pathogenicity measurement and identified pathogenic strains of R. solanacearum. The capacity of strains detected in utilization of three kind of disaccharide (maltose, lactose and cellobios) and three sorts of hexyl alcohol (mannitol, dulcitol and sorbitol) and deoxidization of KNO₃ and the tests of host range, infiltration, melanin formation and dividing pathotype varieties reactions showed the dividing results of biovar, physiological race and pathotype of R. solanacearum from tobacco in chongqing. The detailed experimental results are as follows.1. Several bacteria isolates were separated from typical disease samples in tobacco planting area in Chongqing by selecting single bacterial colony on media. And then, these isolates were cultured on NA, PDA and TTC media. The flagellum pigmentation, morphologic observation and pathogenicity measurement were tested by inoculation to identify tobacco variety Yunyan 85, and 44 pathogenic strains of R. solanacearum were selected, which was come from Qianjiang district, Youyang county and Wulong county in Chongqing.2. At the same condition, time of tobacco showing symptom by injecting stalk and needle pricking axil was less than that by irrigating injured root with bacteria solution. Time of tobacco showing symptom by injecting stalk and needle pricking axil was 3 or 4 days when irrigating injured root with bacteria solution was about 10 days. Time of tobacco getting disease to death by injecting stalk and needle pricking axil was less than that by irrigating injured root with bacteria solution. Besides, some tobacco plants by irrigating injured root didn't die though got disease.3. All 44 strains of R. solanacearum could utilize maltose, lactose, cellobios, mannitol, dulcitol, and sorbitol and produce acid. All strains could deoxidiz KNO₃, produse N₂ and bring nitrite. According to standard of dividing biovars of R. solanacearum all strains belonged to Biovar III and no sub-biovar or other biovar was found.4. Based on the physiological race hosts reactions all 44 strains had pathogenicity which was different in different kind of host. All strains had strong pathogenicity overall. The most strong pathogenic strains were 5-2-4, 5-4-5, 5-3-4, 5-1-4, 5-11-1, 5-8-2, 5-4-4, 5-9-1, 5-23-1 and 5-21-1 from Shuitian town, Xinghua town in Qianjiang county and Huangying town, Xinnvshan town in Wulong county respectively. Tobacco, potato, tomato and eggplant were hypersensitive while capsicum and peanut were less hypersensitive. The tobacco leaves infiltrated by the strains could caused necrotic spots in 24-60 hours. The strains inoculated in the Ltyrosine medium could produce melanin. The results showed all the tested strains belonged to physiological race 1.5. According to tobacco dividing pathotype hosts reactions, all strains were classified into Pathotype I and Pathotype II. Pathotype I were the moderately virulence strains with average disease index was 75.01 (6.82% of all strains) . Pathotype II were the high virulence strains with average disease index was 89.48 (93.18% of all strains) . No low virulence strains. Pathotype I in strains tested were 6-2-1, 6-1-1 and 6-1-2 from Dashiba town in Qianjiang county and Huangying town in Wulong county respectively when other strains belonged to Pathotype II.