Celery flavonoid-rich extract significantly reduces cucumber powdery mildew severity and enhances plant defense responses

This study assesses the antifungal efficacy of celery flavonoid-rich extract (CFRE) against cucumber powdery mildew, caused by Podosphaera fusca, in a controlled greenhouse setting. The application of CFRE at a concentration of 4 mg mL^{- 1} resulted in a remarkable 97% reduction in disease severity. High-performance liquid chromatographic (HPLC) analysis identified apigenin as the predominant flavonoid in CFRE. Furthermore, CFRE treatment induced a robust defense response in cucumber leaves, marked by elevated levels of flavonoids, phenolics, chlorophyll, and defense enzymes such as β-1,3-glucanase, chitinase, peroxidase, phenylalanine ammonia-lyase, and polyphenol oxidase. The study also observed upregulation in the expression of three investigated genes associated with β-1,3-glucanase, chitinase, and phenylalanine ammonia-lyase. Notably, a positive correlation was established between the activity of defense enzymes and their gene expression, as well as between defense enzymes and antioxidant compounds. These findings underscore the potential of CFRE as an environmentally benign alternative to chemical fungicides for managing P. fusca infections.