Isolation and Characterization of Ralstonia solanacearum Causing Bacterial Wilt of Tomato in Nigeria

Bacterial wilt of tomato, caused by Ralstonia solanacearum (Rs), is endemic in most tomato-growing areas of Nigeria, causing 60 to 100% loss in yield.Control measure requires definite information on race and biovar characteristics of the pathogen in those endemic areas.Soil samples were collected from seven states in Nigeria known for high incidence of tomato bacterial wilt.Isolations were performed on triphenyl tetrazolium chloride (TZC) and casamino peptone glucose (CPG) media.Morphological characterization of the pathogen was through simple staining, streaming and KOH solubility test.Molecular confirmation of pathogen's identity was through PCR amplification of genomic DNA using Rs-specific 759/760 primers (f:5'-GTCGCCGTCAACTCACTTTCC-3'; r:5'-GTCGCCGTAGCAATGCGGAATCG-3').Race was determined through hypersensitive reaction on tobacco leaves and biovar characterization was through carbohydrate utilization test.Thirty-four bacterial isolates showed the characteristic creamy white colour on TZC + CPG medium. .The isolates also amplified at 280 bp, confirming the pathogen as Rs.Thirty isolates belonged to Race 1 Biovar III while four belonged to Race 3 Biovar II.The findings are relevant while devising a more targeted management approach to bacterial wilt of tomato in Nigeria.