Submerged fermentation of Colletotrichum truncatum for biological control of scentless chamomile

Abstract

An isolate of Colletotrichum truncatum (Schwein.) Andrus & W. D. Moore is a promising bioherbicide candidate against scentless chamomile (Matricaria perforata Mérat), a noxious weed in western Canada. A major constraint in the development of this bioherbicide is the inefficiency of inoculum production. The objective of this study was to explore submerged fermentation for mass production of C. truncatum.A defined basal salts medium (DBSM) was used for liquid culture with glucose and casamino acids selected as the optimal carbon (C) and nitrogen (N) sources, respectively. Spore yield and biomass production were significantly higher when the DBSM glucose concentration was 35-40 g/L compared to lower concentrations, while inoculum efficacy was significantly greater when produced at 5-10 g/L than at 40 g/L of glucose. Spore yield in baffled flasks at 200 RPM shaker speed was significantly higher than in regular flasks at lower shaker speeds. Under conditions of high aeration, glucose concentration had a significant effect on spore yield, biomass production, and efficacy, whereas the effect was not significant at low aeration. Specific spore and biomass yields also increased significantly with increasing glucose concentrations at high aeration. The scale of submerged fermentation was increased to 20-L fermentors, with dO levels of 10%, 30%, and 60% maintained by agitation and airflow controls. Further study will be required to optimize spore yields at the large scale. This study led to development of a protocol for production of C. truncatum spores using submerged fermentation. Inoculum produced with this method can be used for laboratory, greenhouse, and field trials in development of the bioherbicide.