Trichoderma strain-dependent direct and indirect biocontrol of Fusarium head blight caused by Fusarium graminearum in wheat

Fusarium head blight (FHB), caused by Fusarium graminearum (Fg), is a major disease of wheat not only due to crop yield losses but also because of food safety concerns, since Fg produces toxic trichotecenes, such as deoxynivalenol (DON). Different Trichoderma strains have shown biocontrol efficacy against various Fusarium spp. in a wide variety of pathosystems. In this work, the efficacy of T. asperellum T25, T. harzianum T136 and T. simmonsii T137, was assessed against Fg ITEM 124 in in vitro tests, which included dual cultures, as well as cellulose and cellophane membrane assays. The three Trichoderma strains inhibited Fg growth to varying degrees. However, only T25 and T136 demonstrated control of FHB in wheat when applied to spikes. By quantitative real-time PCR (qPCR) we analysed the expression of eight plant defence-related marker genes in wheat spikes inoculated with Trichoderma, or not, and subsequently infected with Fg. Only wheat spikes pre-treated with T25 or T136 look to activate the salicylic acid-dependent defence, in response to pathogen infection. Expression of tri genes, involved in DON biosynthesis, was analysed by qPCR in dual-culture Trichoderma-Fg confrontations in two different media, and in the plant spikes. Confrontation results indicated that tri gene expression depends on the Trichoderma strain and the culture medium, but the three Trichoderma strains reduced the expression of tri5 in the plant. Results show that T. asperellum T25 reduced FHB disease index by more than 60 %, and was the most effective biocontrol agent, employing direct mechanisms to limit Fg growth and indirect mechanisms by priming local plant defences.