Evaluation of application regimes and rates of biological control agents for the management of root knot nematodes and bacterial wilt of tomato
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Trichoderma asperellum and Bacillus subtilis have been used as biological control agents (BCAs) for root knot nematodes (Meloidogyne spp.) and bacterial wilt (Ralstonia solanacearum), two of the most problematic soil borne pathogens in tomato production. Unfortunately, use of these BCAs is hindered by lack of protocols that farmers can adopt and adapt to their production spheres. The current study developed a working protocol for the appropriate use of T. asperellum strain TRC 900 (1 × 109 spores/ml) and B. subtilis strain BS-01 (1 × 1010 CFU/ml) in the management of root knot nematodes and tomato bacterial wilt disease. Specifically, the appropriate application interval and amount of T. asperellum and B. subtilis that individually or in combination can effectively control RKNs and bacterial wilt in tomatoes were developed. Experiments were established with three application rates of a T. asperellum and B. subtilis (1 ml/L, 2 ml/L and 4 ml/L) and three application interval (3 days, 7 days and 14 days); tested alongside a positive check of Velum Total® (AI: Imidacloprid and Fluopyram) and a negative check where water was used. Bacillus subtilis was tested in the field, screen house and in-vitro whereas T. asperellum and the combination of the two BCAs were tested only in the screen house. The in-vitro trial aimed at determining the potential of B. subtilis to inhibit growth of R. solanacearum included a positive control of an antibiotic Chlortetracycline hydrochloride and water as the negative control. Trichoderma asperellum used at 4 ml/L water every 7 days was the most appropriate for the control of RKNs. However, use of B. subtilis at all the rates and intervals tested had a very low biocontrol efficacy against R. solanacearum. The strain of B. subtilis used did not effectively control bacterial wilt and hence not feasible for use against this particular pathogen at any of these application rates and intervals. When the two biocontrol agents were used in combination, RKNs were effectively managed but bacterial wilt disease was not effectively controlled.