# In Vitro Assessment of Essential Oils as Sustainable Antifungal Agents Against Sclerotinia sclerotiorum Causing Lettuce Drop

## TL;DR

This study tests essential oils as natural antifungal agents against a fungus that harms lettuce crops, finding some oils effective but with varying plant toxicity.

## Contribution

The study introduces essential oils as sustainable alternatives for managing Sclerotinia sclerotiorum in lettuce production.

## Key findings

- Thymus vulgaris essential oil completely inhibited S. sclerotiorum mycelial growth at all tested concentrations.
- Rosmarinus officinalis showed minimal phytotoxicity on crops, making it a promising candidate for sustainable use.
- Field trials are needed to optimize essential oil application protocols to avoid phytotoxicity risks.

## Abstract

Sclerotinia sclerotiorum is a soilborne fungal pathogen, and it is a major threat to lettuce production, causing lettuce drop. This study evaluated the antifungal effectiveness of five essential oils (EOs) (Rosmarinus officinalis, R. officinalis var. verbenone, Lavandula hybrida, Origanum majorana, and Thymus vulgaris) at 0.1%, 1%, and 10%, along with their phytotoxic effect in the field on three different crops (lettuce, tomato, and chard) following foliar application. T. vulgaris EO completely inhibited S. sclerotiorum mycelial growth at all tested concentrations. R. officinalis, L. hybrida, and O. majorana also showed full inhibition at 1% and 10%, while R. officinalis var. verbenone achieved 80–100% inhibition. R. officinalis had the least phytotoxic effects, with only a minimal effect on chard at 1%. R. officinalis var. verbenone caused low/moderate phytotoxicity in lettuce and chard but had no toxic effect on tomato. L. hybrida and O. majorana had moderate to low effects, while T. vulgaris was the most phytotoxic, significantly affecting lettuce and tomato at 1%. Further field trials are needed to define EO application protocols toward sustainable lettuce drop management without risks of phytotoxicity.