Agro-physiological responses and molecular docking evaluation of some essential oils and ascorbic acid as eco-friendly inhibitors of powdery mildew in cucumber plants

Introduction – Powdery mildew is a major fungal disease affecting cucumber production, often managed using synthetic fungicides with environmental and health concerns. This study investigates plant-derived essential oils and ascorbic acid as eco-friendly alternatives, focusing on their effects on disease control, plant physiology, biochemical defenses, and molecular resistance mechanisms. Methods – Two greenhouse experiments were conducted using garlic oil, cumin oil, ascorbic acid, a commercial fungicide (Topas), and an untreated control. Antifungal activity was evaluated alongside plant growth, physiological traits, and yield parameters. Oxidative stress markers (H₂O₂ and MDA), antioxidant enzyme activities (PPO and POD), and biochemical compounds (TPC, TFC, TFAA, and proline) were measured. Gene expression of defense-related markers (PR-1 and LOX-1) was analyzed using qRT-PCR. Gas chromatography–mass spectrometry (GC-MS) identified major bioactive compounds, and molecular docking was performed to explore potential antifungal mechanisms. Results – All treatments significantly reduced powdery mildew severity and oxidative stress compared with untreated plants. Garlic oil showed the highest efficacy, followed by cumin oil and ascorbic acid. Disease severity was positively correlated with H₂O₂ and MDA levels and negatively correlated with plant growth, chlorophyll content, and yield. Garlic oil significantly enhanced plant height, biomass, leaf number, chlorophyll content, and fruit yield. These improvements were associated with increased antioxidant enzyme activities and higher levels of phenolics, flavonoids, amino acids, and proline. Gene expression analysis revealed significant upregulation of PR-1 and LOX-1, particularly in garlic and cumin oil treatments. Molecular docking supported the antifungal potential of the identified compounds through stable interactions with key fungal targets. Discussion – Plant-derived essential oils, especially garlic oil, demonstrated strong antifungal activity and the ability to enhance plant defense systems at physiological, biochemical, and molecular levels. These findings highlight their potential as safe, sustainable alternatives to synthetic fungicides for managing powdery mildew in cucumber cultivation.