Role of organic amendment composition and soil texture in modulating volatile fatty acids, Fe/Mn reduction, and Fusarium oxysporum suppression during anaerobic soil disinfestation

Authors: LITTRELL, JAMES - University Of Tennessee; OWNLEY, BONNIE - University Of Tennessee; Hansen, Zachariah; GWINN, KIMBERLY - University Of Tennessee; BUTLER, DAVID - University Of Tennessee

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2025
Publication Date: 5/21/2025
Citation: Littrell, J., Ownley, B.H., Hansen, Z.R., Gwinn, K.D., Butler, D.M. 2025. Role of organic amendment composition and soil texture in modulating volatile fatty acids, Fe/Mn reduction, and Fusarium oxysporum suppression during anaerobic soil disinfestation. Phytopathology. https://doi.org/10.1094/PHYTO-12-24-0423-R.
DOI: https://doi.org/10.1094/PHYTO-12-24-0423-R

Interpretive Summary: Soil-dwelling plant pathogens pose a risk to many agricultural products. Chemical fumigation has been used for many years to suppress soilborne diseases, but such practices pose environmental and human health risks. A promising alternative to traditional fumigation is called anaerobic soil disinfestation (ASD), in which soil is amended with organic materials, irrigated, and tarped to induce anaerobic fermentation for a brief period before planting. ASD suppresses soilborne plant pathogens through the generation of antimicrobial molecules and compounds like reduced metal cations and volatile fatty acids. However, little is known about the interactions between organic amendment type, soil texture, and liming, and the resulting effectiveness of ASD. We investigated the effectiveness of ASD on the suppression of the important fungal plant pathogen Fusarium oxysporum (Fo), which causes strawberry black root rot, using a combination of several treatments. Three soil textures (sand, sandy loam, and silty clay) and two amendment types (soybean protein and dried molasses) were tested in all combinations with or without lime, and antimicrobial compound concentrations and pathogen survival were measured. Soybean protein resulted in higher antimicrobial compound concentrations, which resulted in greater pathogen suppression. Courser textured soil (sand and sandy loam) resulted in greater pathogen suppression compared to finer textured silty clay soil. Our results highlight the importance of soil texture, soil pH and amendment composition on ASD effectiveness.

Technical Abstract: Less hazardous alternatives to soil fumigants for suppressing soilborne pathogens such as the Fusarium oxysporum (Fo) species complex, one causative agent of the strawberry black root rot complex, are urgently needed. A promising alternative is anaerobic soil disinfestation (ASD), in which soil is amended with labile organic materials, irrigated to field capacity, and tarped to induce anaerobic fermentation for a brief period before planting. ASD suppresses soilborne plant pathogen inoculum via the generation of reduced metal cations (Fe2+, Mn2+) and volatile fatty acids (VFAs, e.g., acetic, n-butyric, and isovaleric). However, little is known about how the interaction between amendment composition, soil texture, and liming influences Fo suppression via soil biogeochemistry. Suppression of Fo by VFAs and reduced metal cations generated during soil fermentation was investigated in soil-based ASD incubation trials in which Fo inoculated sand, sandy loam, and silty clay soils with and without lime (0.1% CaCO3) were amended at 1% w/w basis with varying levels of soybean protein isolate (SPI) and dried molasses (DM), creating a range of protein: carbohydrate ratios from 0.2:1 to 32:1, to initiate ASD treatments. Total soil solution VFA and reduced metal concentrations were negatively correlated with Fo population in sandy and sandy loam soils, and amendment protein concentration was positively correlated with soil solution VFA concentrations in sandy and sandy loam soils. In general, finer soil textures and limed soils were associated with lower Fo suppression. Our results highlight the importance of soil texture, soil pH and amendment composition in influencing ASD effectiveness.