Trichoderma interferes with cold acclimation by lowering soluble sugars accumulation resulting in reduced pink snow mould (Microdochium nivale) resistance of winter rye

• Trichoderma stimulates photosynthesis but decreases the carbohydrate level.
• Applying Trichoderma before cold acclimation decreases M. nivale resistance.
• The sink activity of roots colonized with Trichoderma affects carbon partitioning.
• T. viridae applied with M. nivale after cold acclimation increases pathogen resistance.

We studied the effect of Trichoderma viridae and Trichoderma harcianum applied both before and after cold acclimation treatment on carbohydrate accumulation as well as on the course of pathogenesis caused by Microdochium nivale.Trichoderma applied prior to cold acclimation treatment decreased the resistance of winter rye to M. nivale. The process of cold acclimation was disrupted as levels of soluble carbohydrates in leaves and crowns decreased despite the stimulation of photosynthesis. In contrast to the shoots, the level of carbohydrates in the roots, especially sucrose and nystose, increased considerably. It can be assumed that the sink activity of roots colonized with Trichoderma affected photosynthesis and carbon partitioning. Sucrose, a substrate for the synthesis of fructans and a transport sugar, was probably consumed by Trichoderma fungi, contributing to decreased levels of soluble carbohydrates and, as a result, reduced resistance to snow mould. Comparing the effect of T.viridae applied before and after cold acclimation treatment, the survival rate was significantly higher in the latter. It suggests interactions between both the saprophytic T. viridae and the pathogenic fungus M. nivale when applied together. However, changes induced in fructan metabolism may also contribute to increased resistance to pink snow mould.