Study On Etiology Of Tobacco Bacterial Wilt In Hubei Province

Tobacco bacterial wilt, caused by Ralstonia solanacearum is a typical soil-borne diseases which is widespread in China’s flue-cured tobacco cultivation areas and the disease caused great economic losses in Fujian, Guangxi, Guizhou, Yunnan, Sichuan and Hunan provinces. In recent years, the yield and quality of tobacco in Hubei province were affected seriously by tobacco bacterial wilt as the development of tobacco industry. In this paper, the causal agent of tobacco bacterial wilt from Enshi city in Hubei province was identified and then biovar, race, pathotype, phylotype and sequevar of the pathogen were determined. Subsequently, occurrences of tobacco bacterial wilt in the fields of Enshi were investigated. This study provided useful information for control of tobacco bacterial wilt and resistant cultivar breeding. The results were shown as follows:Diseased samples of tobacco bacterial wilt were collected from Enshi and Shiyan of Hubei in 2013 and 2014, and then 54 bacterial isolates were obtained by using the dilution plate isolation method on selective media TTC. Based on the 16 S r RNA gene sequence analysis and specific PCR detection, the pathogen of tobacco bacterial wilt was identified as R.solanacearum.After testing ability of oxidise carbohydrate(lactose, maltose, cellobiose, mannitol, sorbitol and dulcitol), the 54 strains of R.solanacearum belonged to biovar Ⅲ. According to the susceptibility reaction on six differential hosts(tobacco, potato, tomato, eggplant, pepper and peanut), the 54 strains were pathogenic and determined to be race 1. Pathogenicity of 23 selected strains tested on three tobacco cultivars of different susceptibility was clustered and the results indicated that the 23 strains were divided into three pathogenic types. PathotypeⅠinculding 21.74% of all strains was low virulence and average disease index was 34.59. PathotypeⅡ inculding 39.13% of all strains was moderate virulence with 59.02 of average disease index. The 39.13% of all strains of Pathotype Ⅲ were high virulence with 81.33 of average disease index.Phylotype of the 54 isolates were identified as phylotypeⅠ(Asia branch) by multiplex PCR, and the results showed that specific bands of fragment sizes of 280 bp and 144 bp were amplified on all isolates. Based on analysis of partial sequence of egl gene and mut S gene of R.solanacearum, the 54 isolates were divided into three different sequence variants from phylotypeⅠ(15,17 and 44). Sequence variants 17 and 44 were dominant in Enshi tobacco-growing areas while sequence variant 15 was frequently found in Shiyan.Occurrences of tobacco bacterial wilt in Enshi were investigated in 2013 and 2014 growing seasons. Disease sympoms were first observed in early June with light severity, and the disease developed slowly. As the rising of temperatures and increasing of rainfall, the disease increased quickly from mid-July, and reached to the peaks in mid-August until harvest with 90.3-96.1% of disease incidence and 37.3-47.1 of disease index.