Strategies to effectively manage wheat crown rot, primarily caused by Fusarium pseudograminearum, are limited. Inoculation with Trichoderma strains, shown to suppress soil-borne fungal and oomycete diseases of cereals, offer potential to enhance disease management. Wheat crown rot suppressive assays were conducted in cereal cropping soils to assess rhizosphere competence and efficacies of Trichoderma inoculants in the presence of natural soil-borne microbial communities. F. pseudograminearum and Trichoderma colonisation were assessed in rhizosphere soil (RS), crown shoots (CS), crown roots (CR), primary roots (PR) by species-specific qPCR at 84 days post-emergence (grain fill).
F. pseudograminearum actively colonised all tissues, presence in RS being below the qPCR minimum detection threshold. T. gamsii strains A5MH and Tr905 and T. harzianum strain Tr906 significantly (P<0.001) reduced (33 % – 83 %) in planta pathogen biomass and increased (P<0.05) tiller and head numbers by up to 56% and 47%, respectively. Endophytic colonisation of CS, CR and PR by Trichoderma inoculants and the target pathogen was confirmed by recovery from surface sterilised tissues, qPCR and AFLP genotyping.
Assays in soil with natural crown rot inoculum resulted in significantly (P<0.001) greater in planta pathogen biomass compared to introduced inoculum. A5MH, Tr906 and combined (A5MH+Tr906) treatments significantly reduced pathogen biomass (P<0.001) and stem browning (P<0.01) by up to 70 % and 86 %, respectively. Trichoderma colonisation of CS was significantly (P < 0.001) greater in the combined treatment. There was a significant (P<0.001) correlation (r = 0.71) between pathogen biomass (qPCR) and stem browning, indicating that the qPCR assay can be used as an objective measure of crown rot suppression. Strain A5MH resulted in the greatest disease suppression, despite Tr906 having significantly (P<0.001) greater tissue colonisation (48 %). This implies that A5MH may exhibit disease suppressive mechanisms other than pathogen competition.