To grow, or not to grow: mode of action of plant growth promotion by the fungus Clonostachys rosea

Sammanfattning

The use of plant-health-promoting microorganisms in agriculture is a sustainable way to achieve higher yields. Clonostachys rosea is a fungal biocontrol agent that can promote plant growth, but the nature of the interaction is unknown. This project investigated if this plant-fungal interaction is direct or indirect by inoculating wheat and Arabidopsis thaliana with six C. rosea strains – three with promoting effects and three with no effects – and observing plant growth parameters and root architecture. For wheat, inoculation with plant health promoting strains resulted in increased shoot and seedling fresh weight (p<0.05), however no differences in root length or lateral root number were recorded. In A. thaliana inoculation with a growth-promoting strain led to significantly shorter and less branched roots (p<0.05) Interestingly, inoculation with a non-promoting strain resulted in plants with roots significantly longer than promoting strains (p<0.01). In contrast to growth promotion, fluorescence microscopy using a YFP auxin reporter A. thaliana lines revealed that non-growth promoting strains had auxin fluorescence comparable to control while promoting strains had visibly higher fluorescence. To investigate indirect effects bioassays using metabolite fractions of three C. rosea strains were conducted. They revealed that the strains contain different antimicrobial compounds against Pseudomonas syringae, Escherichia coli, Botrytis cinerea and Saccharomyces cerevisiae. Our findings point to a species and strain specificity of plant growth promoting effects by C. rosea. In wheat the results indicate an indirect interaction, contrary to A. thaliana where a direct interaction is more likely.