A foliar spray made from two Streptomyces spp suppresses Sclerotinia stem rot on canola and inhibits other fungal pathogens

An Actinobacteria collection isolated from wheat roots for Fusarium crown rot disease control was screened in vitro and on planta for suppression of fungal pathogens of canola and identified two potent broad-spectrum Streptomyces species strains. Antifungal activity from these strains completely inhibited in vitro growth of Sclerotinia sclerotiorum, both when tested using agar plate competition assays or using culture filtrates derived from liquid cultures. Both strains also inhibited growth of the canola pathogens Leptosphaeria maculans and Rhizoctonia solani in plate assays. Microscopy studies found the Streptomyces sp. strains colonised root and leaf tissues of canola seedlings. In seedling-based studies when applied as a foliar spray, cultures or culture filtrates from both strains prevented development of Sclerotinia leaf lesions. In a mature plant glasshouse pot study, foliar spraying of the cultures or culture filtrates significantly decreased Sclerotinia stem lesion and sclerotia development, with culture filtrates providing a higher level of disease control. In dual sprays applied at two flowering stages, an 87–99 % and 100 % reduction of stem lesions or sclerotia development respectively were recorded on plants sprayed with culture filtrate compared to untreated controls; this was equivalent to disease protection provided by a commercial chemical fungicide control. Grain yields in those treatments increased by 30–49 % relative to controls infected with Sclerotinia without protection. The two Streptomyces sp. strains and their culture filtrates identified in this study have potential for biocontrol applications that maintain or improve crop productivity, reducing the need for chemical disease control in agricultural systems.