An antifungal vapour to control Alternaria angustiovoidea, causing postharvest black spot rot in apples

Abstract

Apples are among the most popular nutritious fruits. They are prone to several postharvest fungi, resulting in significant losses in overall production. This study evaluated the potential of developed gel formulations (soft gel and carrageenan-guar gum gel) incorporated with combinations of Monarda citriodora essential oil (MEO) and linalool to control the postharvest black spot rot of apples and to improve their shelf life. The pathogenic fungus was isolated from infected apples and characterised as Alternaria angustiovoidea. In vitro, minimum fungicidal concentrations of MEO, hexanal, and linalool vapour phase showed activity at 1346.15 µL L⁻¹ air, 192.30 µL L⁻¹ air and 192.30 µL L⁻¹ air concentration, respectively. MEO and linalool's in vitro checkerboard assay showed synergy, while the combination of MEO and hexanal was additive. In vivo, the checkerboard assay with MEO and linalool incorporated in soft gel formulation showed a synergistic effect at W3 (MEO 336.54 μL L⁻¹ air and linalool 48.07 μL L⁻¹ air) and X3 (MEO 336.54 μL L⁻¹ air and linalool 24.03 μL L⁻¹ air). The soft gel formulation prevented the pH and total soluble solids of the stored apples from changing, inhibited the breakdown of ascorbic acid, and decreased weight loss. Additionally, the stored apples' total phenolic content and antioxidant activity enhanced. The synergistic combination of MEO and linalool incorporated in soft gel formulation could be a promising postharvest treatment against black spot rot of apples for extended shelf life and for maintaining apple fruit quality during storages.