Identification and application of Streptomyces microflavus G33 in compost to suppress tomato bacterial wilt disease

Abstract

Tomato bacterial wilt caused by Ralstonia solanacearum is the most destructive disease impacting production. Application of bioorganic fertilizer (BOF) containing antagonistic microorganism to suppress tomato bacterial wilt disease may be a promising disease control strategy. Here, we used organic waste materials, specifically biogas residues, cattle manure and rice straw, in composting with antagonistic strain G33 isolated from the rhizosphere soil of a healthy tomato plant to produce BOF. Strain G33 was identified as Streptomyces microflavus by morphological and culturing traits and by 16S rRNA gene sequence analysis. We conducted a field experiment with control treatment, organic fertilizer and BOF-G33 to characterize suppression of tomato bacterial wilt disease. Our results indicate that the optimal combination containing (w/w) 40% biogas residues, 40% cattle manure and 20% rice straw can increase the nutrient contents of the compost product, prolong the thermophilic period and increase the decomposition rate of organic matter and the humification degree. A combination of strain G33 and mature compost produced under optimal conditions resulted in the spore number of 5.75 × 109 CFU/g on the sixth day of fermentation. Field experiments showed that BOF-G33 significantly decreased the incidence of tomato wilt; the disease biocontrol efficiency was 64.4%. In addition, application of the BOF-G33 significantly reduced the pathogenic R. solanacearum populations and increased the abundance of beneficial indigenous flora in the rhizosphere soil, which might have been the key factors in constraining the disease. In conclusion, this study showed that bioorganic fertilizer with Streptomyces microflavus G33 is a potential biocontrol agent for controlling tomato bacterial disease.