Potential inhibition of humic acid against soil-borne pathogenic fungi: A review

Green prevention and control management of soil-borne fungal diseases is a hot topic in agriculture, ecology, and the environment. It is an important way to effectively prevent and control soil-borne fungal diseases, solve soil degradation caused by continuous cropping obstacles, and fulfill the sustainable development of agriculture through revealing the mechanisms of functional substances to develop highly effective soil amendments. Humic acid shows an inhibitory effect on soil-borne pathogenic fungi, such as Fusarium oxysporum, Choanephora cucurbitarum, and Rhizoctonia solani, with the inhibition rate exceeding 80%. The molecular and elemental composition and contents of –COOH, phenolic C, methoxy group C, carboxyl C, aromatic C–O, anomeric C, and other functional groups of humic acid have been inferred to be responsible for its inhibitory effects on pathogenic fungi in previous research. The inhibitory mechanisms mainly include cell physiological morphology, biochemical process reactions, and molecular signal transduction. This review systematically summarizes the chemical structure, fungistatic effects, variable characteristics, and inhibitory mechanisms of humic acid, aiming to provide a theoretical basis for the development of green and efficient prevention and control technologies for soil-borne fungal diseases.