Neem Leaf Powder Reduces Ralstonia solanacearum Population Density, Bacterial Wilt Severity and Enhances Tomato Fruit Yield

Abstract Bacterial wilt caused by Ralstonia solanacearum is a major threat to global tomato production. Two field trials were conducted in 2023 (wet season) and 2024 (dry season) at the Federal University of Kashere, Gombe State, to evaluate the use of neem leaf powder in the management of bacterial wilt of tomato. The experiment was conducted using a randomized complete block design with three replications. Neem leaf powder ( Azadirachta indica ) was applied to two tomato cultivars, ‘Tandino’ and ‘Dan Syria’, at 15, 30, and 45 g, while untreated (0 g) and streptomycin-treated plots served as negative and positive controls, respectively. Application of streptomycin and 45 g of neem leaf powder 9 weeks after transplanting showed population densities of 1.5 and 1.4 total cfu·g −1 soil (2023) and 1.4 and 1.0 cfu·g −1 soil (2024), which were significantly lower than the population densities of 8.6 (2023) and 8.0 (2024) cfu·g −1 soil recorded in untreated plots. After application of streptomycin and 45 g of neem leaf powder, wilt severity scores of 0.7 and 1.3 (wet season) and 0.7 and 1.0 (dry season) were observed, which was significantly lower than 5.0 in each season in untreated plots. Application of 45 g neem leaf powder resulted in a yield of 432.4 and 437.4 g of fruit per plant, which was significantly higher than the 2.8 and 2.4 g on untreated plots in 2023 and 2024, respectively. It was found that application of 45 g of neem leaf powder can reduce the severity of bacterial wilt in tomatoes and thus increase fruit yield.