Trichoderma species isolated from grapevine with tolerance towards common copper fungicides used in viticulture for plant protection.

Background: Copper-containing fungicides are applied broadly in organic viticulture against downy mildew caused by Plasmopara viticola. Although long-term application of copper-based fungicides is associated with ecotoxic effects on the environment, their use in viticulture is required until sustainable alternatives are available. Trichoderma spp. might be a promising approach to fungicide reduction while promoting plant growth and development and displaying biocontrol activity. This study aims to examine the tolerance and compatibility of Trichoderma spp. to copper fungicides. This work contributes to the development of a spray application consisting of a copper-tolerant Trichoderma sp. combined with a downscaled copper fungicide rate against P. viticola.

Results: Trichoderma spp. isolated from grapevine wood in vineyards were identified and used for tolerance screening in various concentrations of copper fungicides. Copper hydroxide was identified as being highly compatible with Trichoderma. Two Trichoderma candidates, T. koningiopsis and T. harzianum, showed high copper tolerance in mycelial growth and germination tests, and were adapted to 2.85 g Cu L of the selected fungicide. Microscopic investigations showed the attachment of copper compounds to fungal cell walls and copper uptake within the cytoplasm. In the case of high tolerance, large-scale copper uptake was prevented.

Conclusion: Our findings identified two highly copper-tolerant Trichoderma isolates with natural adaptation to the vineyard ecosystem, which could be further tested as biostimulants and biocontrol agents, combined with a reduced fungicide rate for sustainable plant protection. © 2022 Society of Chemical Industry.