Volatile fatty acid concentration, soil pH and soil texture during anaerobic soil conditions affect viability of Athelia (Sclerotium) rolfsii sclerotia

Volatile fatty acids (VFAs) play a role in suppression of plant pathogens during anaerobic soil disinfestation (ASD), but it is unclear how VFAs in anaerobic soil affect Athelia rolfsii (formerly Sclerotium rolfsii ). Anaerobic growth chamber trials were conducted to evaluate effects of VFA and VFA concentration, and interactions with soil pH and soil texture, on A. rolfsii sclerotia viability (as indicated by sclerotia germination) and colonization by potential mycoparasites. In the first objective, sclerotia were exposed to acetic or n -butyric acids at 4, 8, or 16 mmol/kg soil in sandy soil; soil pH was buffered to 5, 6, or 7. Sclerotial germination was generally reduced by both VFAs, notably at pH 5 (29% germination at 4 mmol/kg soil, 1% at 8 mmol/kg soil, and 0% at 16 mmol/kg soil). The highest colonization rates were observed in acetic acid at 16 mmol/kg soil and soil pH of 5 and 6 (65 and 55% colonization). Sclerotial germination in water or HCl controls was consistently above 90%, with minimal colonization. In the second objective, sclerotia in sandy or sandy loam soil were exposed to 4 or 16 mmol VFA/kg soil at soil pH 5 or 6. Sclerotial germination was generally less in sandy soil compared to sandy loam soil (e.g., 4 mmol VFA/kg soil at pH 5, 62% germination in sandy loam versus 0% in sandy soil), but not at pH 5 and 16 mmol/kg soil (< 1% germination in both soil textures). Soil colloid (clay and organic matter) concentration likely plays a role in reduction of VFA activity. VFAs are probable important factors in A. rolfsii suppression due to ASD treatment in many soil environments, and activity is dependent on VFA concentration, soil solution pH, and soil texture.