Biological soil disinfestation using bioethanol fermentation products: role of residual organic substances

Abstract

We evaluated the efficacy of biological soil disinfestation (BSD) using bioethanol fermentation products (ethanol fermentation solution and crude alcohol) from forage rice plants and sweet sorghum to control the soil-borne pathogen Fusarium oxysporum f. sp. lycopersici (Fol), which causes Fusarium wilt of tomato. In the pot tests, the survival of bud cells markedly declined after 14 days in the soil saturated with diluted bioethanol fermentation products, which contained more than 0.25 % (v/v) ethanol. In the Fol-suppressed soil, a sudden drop of soil oxidation–reduction potential (ORP) below −200 mV and accumulation of acetic acid and Fe2+ were observed during the disinfestation treatment. The bioethanol fermentation products included a certain amount of organic acids (e.g., acetic acid and l-lactic acid) and sugars (e.g., d-glucose, sucrose, and d-xylose), and the treatment with each of these organic substances, as well as ethanol, had a fungicidal effect against Fol in the soil. Thus, the residual organic substances in the bioethanol fermentation products seemed to enhance the fungicidal effect of the ethanol-based BSD treatment. BSD tests in field soil were repeated four times during the spring and autumn for 2 years. Fol was strongly suppressed in the soil that was irrigated with 0.5 or 1.0 % (v/v) bioethanol solution and subsequently covered with a plastic film for 21 days, while the treatment with wheat bran or 1.0 % (v/v) ethanol did not always suppress Fol.