Pathogen Identificaiton Of Tobacco Bacterial Wilt In Shandong And Screening Of Effective Agrochemicals And Antagonistic Bacteria

The bacterial wilt caused by Ralstonia solanacearum is one of the most devastating tobacco diseases. It occurrs in all the tobacco-growing areas, especially in the tropical and subtropical regions. In China, this disease mainly occurred in the south before the1990s. Now the disease spreads rapidly from the south to the north and exists all over the northern tobacco-growing areas. Tobacco bacterial wilt has been an important factor restricting tobacco production because of serious epidemic situation. In this research, we isolated pathogenic bacteria and tested their capacities for utilizing disaccharide (maltose, lactose and cellobios) and hexyl alcohol (mannitol, dulcitol and sorbitol). We tested the resistance of different tobacco cultivars to R. solanacearum and screened effective agrochemicals and biocontrol bacterial strains that were able to suppress the growth of R. solanacearum through laboratory experiments. The main results of this study were as follows:We isolated2pathogenic bacteria from diseased plants collected from tobacco-growing areas of Linyi and Weifang. Shandong Province. The tobacco leaf showed typical characteristic of hypersensitive response by12hours post injection of pathogen suspension. The pathogenic bacteria were identified as R. solanacearum through analysis of16S rDNA sequence. The strains belonged to biovar III as they could utilize lactose, maltose, cellobiose, mannitol, sorbitol and dulcitol and produce acid. We found no tobacco cultivar highly resistant or immune to the pathogenic bacterium in laboratory and field experiments.Six agrochemicals (3%Tetramycin aqueous lolutions,72%Streptopcin soluble powder,80%Ethylicin emulsifiable concentrate,80%Thiram water dispersible granule,3%Zhongshengmycin wettable powders and75%Cholrothalonil-Myclobutanil wettable powders) showed antibacterial activities. The3%Tetramycin aqueous solutions and72%Streptomycin soluble powder produced inhibition zone of19.10mm and17.03mm, respectively. The effects of various combinations of these six agrochemicals were further investigated. The combinations of Tetramycin and Streptopcin, Tetramycin and Zhongshengmycin, and Tetramycin and Thiram showed best inhibitory effects. The relative control effects of Streptopcin and Thiram to tobacco bacterial wilt in the field amounted to78.63%and64.09%respectively.Biocontrol bacterial strains were isolated from different districts of Shandong Province. We isolated24strains from100soil samples and screened6strains which exhibit inhibitory activity to R. solanacearum. Three strains designated as Tsb, Cla and C2c with best performance were identified as Paenibacillus polymyxa through analysis of16S rDNA sequence. Moreover, the three biocontrol bacterium showed inhibitory activity to14pathogenic fungi including Botryosphaeria berengeriana, Trichothecium roseum, Fusarium oxysporum, Rrizoctonia solani, Curvularia lunata.