Role of substrate decomposability and volatile fatty acids in anaerobic soil disinfestation activity against Sclerotinia sclerotiorum

U. Shrestha, R.L. Collins, K.J. Swilling, B.H. Ownley, D.M. Butler
Sclerotia of Sclerotinia sclerotiorum function as survival structures and disease inoculum and are particularly difficult to control by anaerobic soil disinfestation (ASD). The impact of ASD at moderate soil temperatures (15-25°C) on sclerotial germination, production, and colonization by potential antagonists was assessed in field (high tunnel), greenhouse, and lab studies. In the field, ASD amendments representing a range of hypothesized substrate decomposability to soil microbial communities were established with six replicates per treatment in each of two high tunnels. The greenhouse pot study included field treatments and additional substrate treatments. To assess the effects of volatile fatty acids (VFAs) during ASD, treatments exposed to acetic or n-butyric acid (16 mmol kg-1 soil at 4.5 soil pH) were included. Two mesh packets with ten sclerotia each were buried in each replicate, retrieved after three weeks, and assessed. In a lab study, sclerotial germination was assessed following a 3-day exposure to VFAs (acetic and n-butyric acid) at three concentrations (representative of 4, 8, or 16 mmol kg-1 soil) at pH 4.5 or 5.5 and compared to inorganic acid and water controls. In the field, sclerotial germination was similar across treatments, although colonization by antagonists was higher in sucrose and starch-amended treatments (41-45% of sclerotia colonized) compared to the control (24%). In the greenhouse, VFA addition reduced sclerotial germination compared to ASD amendments by >37% and reduced new sclerotia formation by >80% compared to the non-amended control. Sclerotial colonization by zygomycetes (42%) was predominant in n-butyric acid, Trichoderma spp. (71%) in acetic acid, and Fusarium spp. (26%) in sucrose-amended treatments. In the lab study, VFAs suppressed sclerotial germination (20-45% germination) at 16 mmol kg-1 soil and pH 4.5 compared to the HCl control 
(99% germination). VFAs are likely an important mechanism of ASD activity against sclerotia at moderate soil temperatures, and future work should focus on enhancing formation of VFAs in soil.
Shrestha, U., Collins, R.L., Swilling, K.J., Ownley, B.H. and Butler, D.M. (2020). Role of substrate decomposability and volatile fatty acids in anaerobic soil disinfestation activity against Sclerotinia sclerotiorum. Acta Hortic. 1270, 71-82
DOI: 10.17660/ActaHortic.2020.1270.8
anaerobic soil disinfestation, soil amendments, biological control, sclerotia, Sclerotinia sclerotiorum, organic acids

Acta Horticulturae