Greenhouse experiments were conducted to study the effect of plant growth promoting rhizobacteria (PGPR; Bacillus pumilus SE 34, Pseudomonas putida 89B61, BioYield, and Equity), acibenzolar-S-methyl (Actigard), and a soil amendment with S-H mixture (contains agricultural and industrial wastes such as bagasse, rice husk, oyster shell powder, urea, potassium nitrate, calcium super phosphate, and mineral ash) on bacterial wilt incidence caused by Ralstonia solanacearum (race 1, biovar 1) in susceptible tomato (Lycopersicon esculentum cv. Solar Set). In experiments with PGPR, Pseudomonas putida 89B61 significantly reduced bacterial wilt incidence when applied to the transplants at the time of seeding and 1 week prior to inoculation with Ralstonia solanacearum. BioYield, a formulated PGPR that contained two Bacillus strains, decreased disease significantly in three experiments. Equity, a formulation containing more than 40 different microbial strains, did not reduced wilt incidence compared with the untreated control. With inoculum at low pathogen densities of 1 × 10⁵ and 1 × 10⁶ CFU/ml, disease incidence of Actigard-treated plants was significantly less than with nontreated plants. This is the first report of Actigard-mediated reduction of bacterial wilt incidence in a susceptible tomato cultivar. When PGPR and Actigard applications were combined, Actigard plus P. putida 89B61 or BioYield reduced bacterial wilt incidence compared with the untreated control. Incorporation of S-H mixture into infested soil 2 weeks before transplanting reduced bacterial wilt incidence in one experiment. Combination of Actigard with the S-H mixture significantly reduced bacterial wilt incidence in tomato in two experiments.

Biological control of plant diseases with antagonistic bacteria is a promising alternative to conventional chemical control strategies. In vitro screening for inhibition of mycelial growth of phytopathogenic fungi by bacterial isolates is the first step in selecting putative bacterial biocontrol agents. Dual culture plate assay is the most common method involved in this first‐line selection process. However, it needs independent agar plates to test antagonism by a specific bacterial isolate against each of the fungal phytopathogen. Two modified in vitro antagonism tests are proposed here. Antagonistic activity of a putative biocontrol bacterial strain against four different fungal phytopathogens could be assessed in a single agar plate simultaneously. A comparison of the new methods with conventional dual culture plate assay was also done. The proposed methods are easy to perform and results of antagonism are obtained rapidly. Results of fungal inhibition were qualitatively comparable with that generated through dual culture plate assay. Quantity of resources such as agar medium and plates required for the modified antagonistic assays is several folds less than that required for dual culture plate assay.