Morphological and Biochemical Characterization of Strains of Ralstonia solanacearum, Causal Agent of Bacterial Wilt in Tomatoes in Cameroon and Screening of Virulent Strains

Ralstonia solanacearum is a major constraint in tomato production. The aim of this work was to identify the different biovars and races of R. solanacearum which infect tomato plants in Cameroon and determine the most virulent in a gnotobiotic environment. Thirty (30) samples were collected in the field of 03 different agro-ecological zones considered as major tomato production area in Cameroon. The bacteria were isolated on modified Kelman solid medium, and identified based on morphological and biochemical characterization. The pathogenicity test was performed in a gnotobiotic environment by root inoculation. Twenty-nine (29) isolates showed colonies characteristic of virulent strains. Water, motility, catalase, KOH, Kovac oxidase, glucose reduction, and sucrose tests were positive. However, gram staining, spore production, arginine test and sulfate reduction were negative. The biovar tests carried out revealed the presence16.66% biovar 2 (bv 2) and 76.66% biovar 3(bv 3). The tobacco hypersensitivity tests carried out revealed the presence of two (02) races: race 1 and race 3 (majority). A predominance of race3 biovar 3 was observed in Cameroon. Results from pathogenicity test revealed that two (02) strains, FM6 (race 3 bv2) and BFo (race 3 bv 3) were high virulent, causing up to 100% loss of seedlings on the sixth day post-inoculation.