Selection, Formulation, and Field Evaluation of Bacillus amyloliquefaciens PMB01 for Its Application to Manage Tomato Bacterial Wilt Disease

Bacterial wilt caused by the soil-borne pathogen Ralstonia solanacearum is one of the most devastating diseases in solanaceous plants. No agrochemicals are available to manage bacterial wilt effectively. A Bacillus amyloliquefaciens strain designated PMB01 was recovered from the cabbage rhizosphere and was found to be capable of inhibiting the growth of R. solanacearum. The PMB01 strain was highly resistant to extreme pH, heat, high salt salinity, and various fungicides. In contrast, PMB01 was sensitive to copper-based compounds, streptomycin, and tetracycline. The efficacy of the PMB01 strain in suppressing R. solanacearum and bacterial wilt in tomatoes was significantly improved when the culture medium was supplemented with 1% (w/v) soybean meal. PMB01 was in a 500-liter tank for the pilot production, and the resultant broth could effectively reduce the severity of tomato bacterial wilt in greenhouse trials. The PMB01 fermentation broth was mixed with 10% corn starch and 30% maltodextrin to make a wettable powder (WP). PMB01 could survive in the wettable powder for more than two years without losing its antagonistic activity. In ten field trials, tomato plants treated with 50, 100, or 200-fold dilutions of PMB01 WP reduced bacterial wilt severity by more than 67% compared to the mock (water control) treatment. This work revealed that the effectiveness of the rhizobacterium PMB01 to antagonize R. solanacearum was greatly improved when the culture medium was supplemented with 1% (w/v) soybean meal, indicating that PMB01 is an ideal bio-agent candidate. A durable format suitable for storage was also developed. Similar concepts may be applied to other bio-agent candidates to improve their effectiveness in disease management.