Mitigation of junglerice (Echinochloa colona) allelopathic stress in rice (Oryza sativa L.) by Bacillus subtilis

Abstract

Rice (Oryza sativa L.) is one of the world’s major staple crops due to its nutritional value and associated physiological and health benefits. However, rice production faces a serious threat from Echinochloa colona (junglerice), an aggressive and difficult-to-control weed. E. colona releases allelochemicals into the environment that suppress rice seed germination and seedling growth. In this study, we investigated the potential role of the beneficial bacterium Bacillus subtilis in alleviating allelopathic stress. As a plant growth-promoting rhizobacterium, B. subtilis enhances plant health by producing biologically active compounds and improving nutrient uptake. In vitro bioassays were conducted to evaluate the allelopathic effects of aqueous extracts prepared from different parts of E. colona (inflorescences, shoots, and roots) on rice. Extract concentrations ranging from 0.2% to 3.0% significantly inhibited seed germination, seedling biomass, and root and shoot lengths compared with the control. Application of B. subtilis significantly mitigated these adverse effects, improving seed germination by up to 73%, root length by 34.56%, shoot length by 20%, fresh biomass by 27.9%, and dry biomass by 6.8% relative to untreated stressed plants. Enhanced biomass production and seedling growth following B. subtilis application were further illustrated by heatmap analysis. A concentration range of 1.0% to 1.8% of B. subtilis was most effective in promoting overall seedling growth and reducing the negative effects of weed-induced allelopathic stress. These findings demonstrate that B. subtilis is a promising biocontrol agent for mitigating allelopathic interference from E. colona, thereby improving the growth and development of rice seedlings.