Heterogeneity of pathogenicity of Ralstonia solanacearum strains isolated from potato fields in Hamadan province

Abstract
One of the most devastating potato diseases in Hamadan province is bacterial wilt caused by Ralstonia solanacearum. The production of extracellular polysaccharide is the most important pathogenic factor of this bacterium. To investigate the heterogeneity of pathogenicity among pathogenic strains of bacteria, plant samples suspected of contamination were collected from the potato growing areas of the province. In the laboratory, bacterial strains of R. solanacearum were isolated from infected potato samples on Nutrient Agar (NA) containing tri–phenyl tetrazolium chloride (TTC). Screening of isolated bacteria was done based on colony appearance on TTC culture medium, hypersensitivity reaction on tobacco & tyrosinase activity. A total of 63 bacterial strains were selected & their critical phenotype were characterized. To select representatives of bacterial strains for greenhouse experiment, hypersensitivity reaction on tobacco and pathogenicity on potato and geranium were investigated for all strains. The pattern of bacterial cell soluble proteins electrophoresed in polyacrylamide gel was investigated. Results showed that most of the strains showed hypersensitive reaction on tobacco & they were pathogenic on potato & geranium. In a separate experiment, bacterial strains were grouped based on the severity of pathogenicity on geranium leaves & the obtained data were analyzed with SAS software. Finally, based on the appearance & phenotypic characteristics of bacterial strains, the pattern of electrophoresed cell soluble proteins, pathogenicity in geranium & hypersensitivity reaction on tobacco, 10 representative strains were selected to investigate the heterogeneity of pathogenicity on potato and tomato in greenhouse. In greenhouse conditions, the variation of pathogenicity among the selected strains on potato & tomato was investigated in a randomized complete block design with three replicates. Results showed that the tested strains were heterogeneous in terms of pathogenicity in both potato & tomato plants and showed significant differences. In some cases, tested strains were up to five statistical groups based on the effect on plant growth factors such as epinasty, plant total weight, wet and dry weight of upper parts & roots. This important finding can clarify our point of view on the control of bacterial wilt disease of these two very important products based on the use of resistant or tolerant cultivars & integrated control and open a new window for us to efficient control of the disease.
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