Wheat rhizosphere dynamics of Trichoderma gamsii A5MH and suppression of a Pythium root rot-Fusarium crown rot disease complex over two consecutive cropping seasons.

AIMS: Determine the wheat rhizosphere competence of Trichoderma gamsii strain A5MH and in planta suppression of the Pythium root and Fusarium crown rot pathogens Globisporangium irregulare and Fusarium pseudograminearum.

METHODS AND RESULTS: Wheat was continuously cropped (eight years) at a minimum tillage, low growing season rainfall (GSR ≤ 170 mm) site shown as highly conducive to Pythium root and Fusarium crown rots. Root isolation frequency (RIF) and qPCR was used to determine the rhizosphere dynamics of strain A5MH and the target pathogens at tillering, grain harvest and in postharvest stubble over the final two years. Strain A5MH actively colonized the wheat rhizosphere throughout both growing seasons, had high root abundance at harvest [log 4.5 genome copies (GC) g-1] and persisted in standing stubble for at least 293 days postinoculation. G. irregulare was most abundant in roots at tillering, whereas F. pseudograminearum was only abundant at harvest and up to 9-fold greater in the drier, second year (GSR 105 mm). Strain A5MH decreased RIF of both pathogens by up to 40%, root abundance of G. irregulare by 100- fold and F. pseudogaminearum by 700- fold, but was ineffective against crown rot in the second year when pathogen abundance was > log 6.0 GC g-1 root. Strain A5MH increased crop emergence and tillering biomass by up to 40%.

CONCLUSIONS: Further trials are required to determine if the A5MH-induced pathogen suppression translates to yield improvements in higher rainfall regions where non-cereal rotations reduce crown rot inoculum.