Document Type : Research article
Authors
1
Vegetable Diseases Research Department, Plant Pathology Research Institute, Agricultural Research Center, Giza, Egypt
2
Integrated Control Research Department, Plant Pathology Research Institute, Agricultural Research Center, Giza, Egypt
10.21608/aasj.2025.451686
Abstract
Alternaria alternata, the causal agent of potato leaf spot, is a destructive foliar pathogen responsible for major yield losses worldwide, including in Egypt. This study evaluated the efficacy of lemongrass (Cymbopogon citratus) oil microemulsions compared with Index fungicide 77% WP (copper hydroxide) under laboratory, greenhouse, and field conditions. In vitro assays, conducted using the poisoned food technique, showed a clear dose-dependent inhibition of mycelial growth, ranging from 6.3% at 60 µl/ml to complete suppression (100%) at 450 and 800 µl/ml. Greenhouse trials confirmed a concentration-dependent reduction in disease severity, with 300 µl/ml achieving the highest suppression (74.8%), while Index fungicide (250 g/100 L water) consistently provided superior control (87.4%). Biochemical analyses revealed that lemongrass oil significantly increased chlorophyll a and carotenoid contents but had no notable effect on chlorophyll b, suggesting selective stimulation of photosynthetic pigments. Enhanced peroxidase, polyphenol oxidase, and phenolic compound levels indicated activation of host defense pathways, while sugar and flavonoid contents also increased following treatment. Field trials across Beheira, Sharkia, and Qalyubeia governorates confirmed the protective effects of lemongrass oil, with 300 µl/ml consistently reducing disease severity, though less effectively than Index fungicide. Collectively, these findings demonstrate that lemongrass oil microemulsions represent a promising eco-friendly alternative for integrated management of potato leaf spot, with potential to reduce reliance on synthetic fungicides.
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