Trichoderma species show biocontrol potential in dual culture and greenhouse bioassays against Fusarium basal rot of onion

Fusarium basal rot (FBR) caused by Fusarium oxysporum f. sp. cepae (FOC) affects onion production worldwide. Despite current control measures, (e.g. 4+ year crop rotations and fungicide application) disease incidence is increasing in Nova Scotia (NS). This increase causes yearly economic losses of up to 20% onion production value in the Annapolis Valley, NS. While Trichoderma species are successfully used as biocontrol agents of many crop pathogens including Fusarium spp., none have previously been tested against FBR of onion in Nova Scotia. Seven Trichoderma species were isolated from agricultural soil of the Annapolis Valley, NS, and identified using ITS rDNA barcoding. Strains were evaluated for biocontrol potential of FOC using dual culture bioassays and greenhouse bioassays on onion. All Trichoderma species tested showed signs of antagonism against FOC in dual culture. Trichoderma hamatum and T. harzianum most frequently elicited multiple signs of antagonism (e.g. creation of a hyphal barrier and overgrowth of FOC), while T. gamsii most inhibited FOC growth. Soil inoculated with 1000 spores per gram FOC produced approximately 65% toxicity in onion seedlings; application of T. atroviride and T. harzianum significantly reduced FBR symptoms in greenhouse grown onions inoculated with FOC. Trichoderma strains antagonistic to FOC have potential for development as biocontrol products for use in Nova Scotia and other onion growing regions.