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

## TL;DR

This study shows that a fungus can cause copper formulations on grapevine leaves to dissolve, potentially improving plant protection against disease.

## Contribution

The novel finding is that fungal presence triggers copper (nano)formulation transformations and partial dissolution, which could enhance targeted plant protection.

## Key findings

- Fungal inoculation caused partial dissolution and complexation of Cu with carboxylate- and thiol-containing compounds.
- Copper did not significantly translocate beyond the exposed leaves, remaining localized.
- Fungal metabolites were identified as key drivers of Cu transformations.

## 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.

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.