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Role of volatile fatty acids in suppression of Sclerotium rolfsii during anaerobic soil disinfestation

Keagan Swilling: University of Tennessee, Plant Sciences

<div>Anaerobic soil disinfestation (ASD) is a non-chemical control method used for soilborne plant pathogens in high value specialty crops. During ASD, volatile fatty acids (VFAs) are produced. Two trials were conducted in an anaerobic chamber to determine if two VFAs found in abundance during ASD (acetic and n-butyric acid) suppressed germination of <em>Sclerotium rolfsii</em>. In trial 1, sclerotia were exposed to VFAs at 4, 8 or 16 mmol/kg soil and soil pH 4.5, 5.5, or 6.5 in sandy soil for 4 days, after which germination was assessed and compared to controls exposed to HCl or water. In trial 2, sclerotia were exposed to VFAs at 4 or 16 mmol/kg soil and soil pH 4.5 or 5.5 in sandy or sandy clay loam soil to assess the impact of clay content on VFAs against <em>S. rolfsii</em>. Sclerotia germination was 60% less than controls in sandy soil with 4 mmol acetic acid/kg soil and 4.5 soil pH; there was no suppression at 5.5 or 6.5 soil pH. At 8 and 16 mmol acetic acid/kg soil, germination was almost 100% less than controls at 4.5 soil pH; 20% to 60% less at 5.5 soil pH; and not suppressed at pH 6.5. Increasing clay content significantly reduced activity of VFAs on sclerotia germination at 4, but not at 16 mmol acetic acid/kg soil. In general, acetic and n-butyric acid equally suppressed sclerotia germination. VFAs are likely an important mechanism of <em>S. rolfsii </em>suppression during ASD, and that activity is significantly affected by VFA concentration, soil pH, and soil type.</div>