Biological Control of Tomato Bacterial Wilt Disease by Endophytic Pseudomonas fluorescens and Bacillus subtilis

BACTERIAL wilt disease caused by Ralstonia solanacearum is a serious threat for agricultural production of tomato. In this study, 80 endophy tic bacterial isolates were isolated from healthy tomato plants in R. solanacearum-infested fields. Two endophy tic antagonists designated HRA32 and HRA69 showing the highest antagonistic activity via in vitro screening were identified as Pseudomonas fluorescens and Bacillus subtilis using 16S rRNA analysis. The selected isolates were evaluated in vitro for their activities related to plant nutrition and plant growth regulation. Both of the assessed endophytes were found to exhibit capabilities in ammonia, indole acetic acid (IAA) and siderophore production as well as phosphate solubilization. Pot experiments were adopted to test the control efficiency against tomato bacterial wilt. Results revealed that HRA32 and HRA69 significantly reduced disease incidence when applied as separate treatments. The clear synergetic effect was observed in tomato plants treated with a mixture of the two antagonists reducing disease incidence significantly from 87.22% in the control to 16.66% with biological control efficacy of 80.23%. It is concluded that application of P. fluorescens HRA32 and B. subtilis HRA69 may be a promising approach for biological control of the tomato bacterial wilt and may play an important role in sustainable agriculture.