Eco-friendly Biocontrol of Ralstonia solanacearum and Plant Growth Promotion in Tobacco Using Garbage Enzyme and Bacillus velezensis A1.

Ralstonia solanacearum, the causative agent of bacterial wilt disease, poses a significant threat to agriculture. The demand for safe and high-quality food has increased interest in biological control agents (BCAs), despite challenges related to stability and cost. Garbage enzymes (GEs) are a promising alternative, rich in beneficial microbes and organic compounds. In this study, four types of GEs (onion, garlic, ginger, and mixed fruit) were individually tested against R. solanacearum in vitro, with only onion GE showing significant inhibition. Filtered onion GE, which lacked any microbes, also showed inhibition; however, its heat-treated form exhibited a reduced inhibitory effect, indicating the role of heat-sensitive compounds in inhibiting R. solanacearum. An antagonistic bacterial strain A1, isolated from onion GE, inhibited pathogen growth by up to 75% through volatile compounds. Cell-free culture filtrate of the strain A1 also inhibited R. solanacearum in vitro. Strain A1 exhibited nitrogen fixation, siderophore production, indole acetic acid (IAA) synthesis, and extracellular enzyme production, positioning it as a potent biocontrol agent. The genome analysis of the strain A1 revealed the presence of several plant growth-promoting genes. In vivo studies with GE, GE-filtered, and strain A1 demonstrated significant pathogen inhibition and promoted tobacco plant growth. Disease incidence was reduced to 26.6% with GE, 46.67% with microbe-free GE, and 40% with strain A1. Overall, these treatments positively impacted plant root and shoot lengths as well as both fresh and dry weights. Our findings highlight onion GE as a potential, environmentally friendly method for controlling bacterial wilt and enhancing plant development, offering an alternative approach to traditional chemical controls in agriculture.