Evidence of copper (nano)formulation biotransformations triggered by Botrytis cinerea on grapevine leaves for targeted plant protection

Abstract

The present work aimed at unravelling if fungal inoculation on grapevine leaves could trigger the dissolution of foliarly deposited Cu (nano)formulations, and how this would impact Cu translocation in planta. Leaves of grapevine seedlings were exposed to 3.3 μg of Cu (5 μg cm⁻²). Formulations of contrasting solubilities (micro-sized conventional Bordeaux mixture, CuO-nanoparticles (CuO-NPs), and CuSO₄) were applied to grapevine leaves, followed by the inoculation of Botrytis cinerea spores on top of the deposited Cu formulations. Nine days after Cu deposition, and six days post inoculation, Cu distribution and transformations were assessed at the leaf surface using micro-X-ray fluorescence and X-ray absorption near-edge structure spectroscopy. Cu was also quantified in non-exposed tissues to evaluate the role of fungal-triggered transformations on Cu translocation. For all non-inoculated formulations, Cu remained largely untransformed at the leaf surface. After inoculation of B. cinerea, Cu was partly found complexed with carboxylate- and thiol-containing compounds, associated with partial Cu reduction, with similar patterns across all (nano)formulations. This was mainly attributed to the presence of fungal metabolites. Despite these transformations, Cu did not significantly translocate in planta, with all the taken-up Cu found on and/or within exposed leaves. This work suggests that these approaches could lead to more efficient plant protection strategies by (i) increasing leaf affinity of Cu-based compounds, while (ii) triggering ionic Cu release thanks to a pathogen-triggered dissolution.