Fungal pathogens are a major challenge in agriculture production, resulting in a significant loss in crop yields and excessive use of chemical fungicides. Antimicrobial resistance among fungal pathogens against conventional fungicides further highlights the need to develop sustainable alternatives. This study aimed to develop photodynamic antifungal treatments using food-grade extracts and compounds with ambient sunlight to create sustainable solutions to control fungal pathogens in agricultural production. The food-grade extracts and compounds evaluated in this study include olive pomace extract (OPE) and curcumin. The efficacy of the photodynamic approach was evaluated against Alternaria alternata on a tomato leaf and Botrytis cinerea on a strawberry plant as model systems, respectively. The results demonstrate a significant reduction (ca. 2.3 log reductions) in the number of culturable A. alternata conidia inoculated on tomato leaf (ca. 4.73 ± 0.21 log conidia/cm²) within 30 min of the photodynamic treatment using OPE and sunlight. Based on the in vivo study, the combined treatment of OPE with sunlight effectively suppressed the spread of Alternaria infection on the tomato leaf. The size of the Alternaria infection increased significantly on the tomato leaf that are treated only with water, OPE, or sunlight within 5-7 days of incubation. In contrast, the photodynamic treated samples showed no significant increase even after 10 days of incubation. The antifungal activity of the combined treatment of curcumin and sunlight was evaluated against B. cinerea infection on a strawberry plant. The number of culturable B. cinerea conidia inoculated on the strawberry plant showed ca. 2.7 log reduction within 30 min of the photodynamic treatment, whereas those treated only with water, curcumin, or sunlight showed ca. 0.0, 0.5, and 1.1 log reductions, respectively. Interestingly, the antifungal efficacy of the combined treatment was further enhanced by depositing the curcumin on the cellulose nanofiber (CNF). The populations of conidia inoculated on the strawberry plant decreased below the detection limit (1.0 log conidia/cm²) within 30 min when treated with CNF-bound curcumin and sunlight. Together, these results suggest a strong potential for photodynamic antifungal treatments using food-grade extracts and compounds as a safe and sustainable antifungal strategy to effectively control plant pathogens on fruits and vegetables.

Yoonbin Kim

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