# Celery and Spinach Flavonoid-Rich Extracts Enhance Phytoalexin Production in Powdery Mildew-Infected Cucumber Leaves

## TL;DR

Celery and spinach flavonoid extracts boost phytoalexin production in cucumber leaves infected with powdery mildew, offering a natural alternative to chemical fungicides.

## Contribution

The study shows that flavonoid-rich extracts from celery and spinach can enhance plant resistance to powdery mildew through phytoalexin induction.

## Key findings

- Spraying with celery and spinach flavonoid extracts increased phytoalexin levels in infected cucumber leaves.
- Phenolic acids and rutin were significantly elevated in treated leaves compared to untreated controls.
- Fluorescence microscopy showed accumulation of phenolic compounds in chloroplasts and epidermal cell periphery.

## Abstract

Phytoalexins are antimicrobial compounds of diverse chemical classes whose production is triggered in plants in response to pathogen infection. This study demonstrated that spraying with a celery flavonoid-rich extract (CFRE) or a spinach flavonoid-rich extract (SFRE) enhanced the production of phytoalexins in cucumber leaves artificially infected with powdery mildew incited by Podosphaera fusca. High-performance liquid chromatographic (HPLC) analysis revealed a noticeable increase in the content of phenolic acids, including caffeic acid, ellagic acid, ferulic acid, gallic acid, p-coumaric acid, and syringic acid, as well as the flavonoid rutin in both non-inoculated and inoculated leaves of cucumber seedlings treated with CFRE and SFRE, compared to healthy untreated leaves used as a control. Fluorescence microscopy revealed the accumulation of phenolic acid compounds in chloroplasts and at the periphery of epidermal cells. Overall, results suggest the reduced severity of P. fusca infection following the application of CFRE and SFRE in cucumber leaves could be due, at least in part, to the production of phytoalexins of polyphenolic nature. These findings provide insights into the mechanisms of systemic resistance induced by CFRE and SFRE. Moreover, they confirm these two natural flavonoid-rich products could be promising alternatives to synthetic chemical fungicides for the safe and ecofriendly control of cucumber powdery mildew.