Effects of Digestate from Swine Manure Digester on in Vitro Growth of Crop Fungal Pathogens: A Laboratory Study

Abstract

<abstract><title><italic>Abstract. </italic></title> Anaerobic digestion is one of the most popular methods for swine manure treatment in China, and the resultant digestates are mainly used as fertilizer on arable land. Residues from anaerobic fermentation may be used to mitigate the use of chemical fungicides, but relevant information is lacking. In this lab-scale study, original digestate (OD) from a swine manure-fed digester and centrifuged supernatant liquid (SL) with different storage times (0, 7, 14, or 28 d) were added to potato dextrose agar (PDA) media at a rate of 5% to investigate the effects on in vitro mycelial growth of seven phytopathogenic fungi: Fusarium oxysporum, Sclerotinia sclerotiorum, Rhizotonia cerealis, Bipolaris sorokinianum, Rhizoctonia solani, Exserohilum turcicum, and Bipolaris maydis. Diameters of the fungal colonies were measured at 1 d intervals for 7 consecutive days, and the absolute growth rate (AGR) and growth coefficient (k) were calculated. Results showed that the colony sizes of Fusarium oxysporum, Sclerotinia sclerotiorum, Rhizotonia cerealis, Bipolaris sorokinianum, and Rhizoctonia solani on the OD-treated media were significantly smaller (p < 0.01) than the corresponding controls regardless of the storage time. Similarly, independent of storage time, SL-treated media were shown to significantly (p < 0.01) suppress AGR compared to the controls for all seven fungi except for Exserohilum turcicum, where no significant difference was observed between the 14-day-old SL treatment and control. The average k values of the fungi on the OD-treated media ranged from 29% to 143% of the values on the SL-treated media. The results of this study suggest potential use of digestate for plant disease control, which would reduce the use of chemical fungicides. Further studies are needed to investigate the fungicidal mechanism and fungicidal efficacy of OD and SL under field conditions.