Co-inoculation of Trichoderma gamsii A5MH and Trichoderma harzianum Tr906 in wheat suppresses in planta abundance of the crown rot pathogen Fusarium pseudograminearum and impacts the rhizosphere soil fungal microbiome

Wheat root endophytic strains Trichoderma gamsii A5MH and T. harzianum Tr906 were assessed for their abilities to suppress in planta abundance of the crown rot pathogen Fusarium pseudograminearum and increase growth of durum wheat. Fusarium crown rot suppressive assays were conducted in natural Kandosol and Chromosol wheat cropping soils with greater disease expression observed in the Chromosol. Rhizosphere abundance of T. gamsii A5MH, T. harzianum Tr906 and F. pseudograminearum were quantified by species-specific qPCR at plant maturity. Strains A5MH and Tr906 actively colonized the wheat rhizosphere and suppressed in planta pathogen abundance in both soil types, with both inoculants persisting in roots and soil to 84 days postemergence. Strain A5MH increased wheat biomass in both soils, whereas strain Tr906 only increased biomass of Chromosol-grown wheat. Metabolites of strains A5MH and Tr906 decreased in vitro growth of wheat pathogenic F. pseudograminearum, Rhizoctonia solani and Pythium irregulare, but did not inhibit either inoculant. Compared with individually inoculated strains, co-inoculation of A5MH and Tr906 did not affect rhizosphere niche abundance, in planta pathogen suppressive efficacies or wheat growth-benefits of either inoculant in Chromosol-grown wheat. Fusarium crown rot symptoms however, only decreased in the A5MH and co-inoculated treatments. Each Trichoderma treatment had distinct impacts on the structure (beta diversity) of the indigenous rhizosphere soil fungal community of Chromosol-grown wheat. Strain A5MH and co-inoculated treatments had the greatest overall effects on soil fungal community (alpha) diversity and structure. Community differentiation was primarily attributed to increased abundance of Trichoderma spp. in the inoculated treatments and associated decreases in plant pathogenic and predominantly saprophytic fungal genera.