SELECTION OF ANTAGONISTIC BACTERIA FOR THE BIOCONTROL OF Ralstonia solanacearum CAUSING BACTERIAL WILT IN TOMATO

Abstract

Bacillus and Pseudomonas are potential bacteria for application in the management of plant diseases in general and bacterial wilt in particular. In this study, Bacillus spp. and Pseudomonas spp. were isolated from tomato-cultivated soils in Lam Dong province and assessed for their antagonistic activity against Ralstonia solanacearum strain CXT3 using the agar well diffusion method. The potential strains were subsequently evaluated for their efficacy in controlling bacterial wilt in vitro, greenhouse and field conditions. All tested bacterial strains demonstrated antagonistic activity against R. solanacearum CXT3. Among them, Pseudomonas spp. ĐHT1, ĐXT1 and Bacillus spp. ĐXT6, CC-LĐ2.2 exhibited strong antagonistic effects, with inhibition zones of 16.7, 16.6, 14.7, and 13.6 mm, respectively. The in vitro preventive efficacy of the four bacterial strains (Pseudomonas spp. ĐHT1, ĐXT1; Bacillus spp. ĐXT6, CC-LĐ2.2) ranged from 69.2% to 95.7% and control efficacy from 61.6% to 92.4%. Based on 16S-rRNA gene sequencing, ĐXT1 was identified as Pseudomonas fluorescens and ĐXT6 as Bacillus amyloliquefaciens. B. amyloliquefaciens ĐXT6 and P. fluorescens ĐXT1 significantly reduced disease incidence and disease index, showing control efficiencies of 76.7% and 65.3%, respectively, at 28 days after planting under greenhouse conditions. They also promoted plant height, root length, fresh weight and dry weight. In field trials, the biological product NLHX at a rate of 3 kg/ha achieved a control efficacy of 70.9%, demonstrating the potential for developing biological products from B. amyloliquefaciens ĐXT6 and P. fluorescens ĐXT1 to manage bacterial wilt in tomatoes.