Organic acids in condensed distiller's solubles: toxicity to soilborne plant pathogens and role in disease suppression.

摘要

Condensed distiller's solubles (CDS), a coproduct of ethanol production from corn (Zea mays), has shown disease suppressing effects when added to pathogen-infested soils and peat-based substrate prior to planting. In this study, CDS amendment (1 and 3 w/w) to a sandy-loam soil displayed a low level of toxicity to microsclerotia of Verticillium dahliae and reduced their germination by 46 to 63 in 1 week in the laboratory soil microcosm tests. The analyses of CDS for the presence of any toxic substances revealed that it contains moderate levels (~144 mmol/L) of volatile (acetic and formic) and nonvolatile (glycolic) organic acids, and some of these are known toxicants. Glycolic, acetic, and formic acids contents were 77.1, 17.7, and 3.9, respectively. Minor concentrations (0.2-0.7 mmol/L) of propionic, n-butyric, isobutyric, n-caproic, and n-valeric acids were also found in CDS. In solution assays, the viability of V. dahliae microsclerotia treated for 24 h in 1, 2, 5, and 10 (v/v) CDS (pH 3.6-4.5) or a mixture of organic acids (pH 3.2-5.0) with the same percent composition as the CDS was reduced by 2, 7, 22, and 48 or 6, 32, 53, and 69, respectively. A mixture of organic acids with the same volumetric ratios as 2 and 4 CDS completely inhibited the growth of Pythium ultimum after treatment of culture plugs for 24 h in solution assays. In growth room bioassays, addition of a mixture of organic as in 1 and 2 CDS (v/w) to a P. ultimum infested muck soil reduced damping-off severity by 45-52 and increased the percentage of healthy seedlings by 164-180 over the control. A pre-planting amendment of glycolic acid (0.075 and 0.15 w/w) to an infested muck soil significantly increased the percentage of healthy cucumber (Cucumis sativus) seedlings by 107 and 122, respectively, and decreased the damping-off severity by 33 and 40, respectively, over the control. This study suggests that organic acids from CDS have a role in disease suppression in sandy-loam and muck soils.