Evaluation of Botanical and Biological Control Strategies Against Onion Purple Blotch Disease in Egypt

Abo-Zaid, Aya H.; Abdel-Wahab, Hala; EL-Samman, Magdy Gad EL-Rab; Helmy, Karima G.

doi:10.21608/ejp.2025.406926.1151

Evaluation of Botanical and Biological Control Strategies Against Onion Purple Blotch Disease in Egypt

Document Type : Original Article

Authors

Plant Pathology Department, Faculty of Agriculture, Ain Shams University, P.O. Box 68, Hadayek Shobra, 11241, Cairo, Egypt

10.21608/ejp.2025.406926.1151

Abstract

Onion is a vital food crop because of its nutritional value and role in food security. However, it remains susceptible to purple blotch disease caused by Alternaria porri. This study evaluated the antifungal potential of various botanical aqueous and oil extracts, as well as biological control agents, against A. porri through in vitro, greenhouse, and field experiments. Garlic extract at 10% demonstrated the highest inhibition rate (37.9%), followed by Bougainvillea extract at 5% and 20%, which achieved inhibition rates of 36.5% and 30.3%, respectively. In contrast, the Moringa extract exhibited minimal antifungal activity. Among the oil extracts tested (25–100 ppm), clove oil was the most effective in vitro, with an EC₉₀ value of 2.09%. In greenhouse trials, 10% of Bougainvillea extract resulted in the lowest disease severity (11.5%). Garlic extract at 5% yielded the longest leaves (41.3 cm), whereas Bougainvillea extract at 5% yielded the widest bulbs (25.2 mm). Neem extract at 5% recorded the highest chlorophyll content (69.39%). Garlic oil at 50 ppm reduced disease severity to 21.3% and at 75 ppm resulted in the widest bulb diameter (23.1 mm). Meanwhile, cinnamon oil at 75 ppm produced the longest leaves (45.9 cm). Trichoderma sp. was the most effective bioagent in reducing disease severity, whereas Chaetomium sp. enhanced leaf length, bulb diameter (26.7 mm), and chlorophyll content. Enzyme assays revealed peak peroxidase activity with Bacillus sp. and the highest polyphenol oxidase activity with garlic oil at 75 ppm. Field results confirmed that garlic oil and Trichoderma sp. were effective treatments.

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