December 2024 JOURNAL OF PLANT AND FOOD SCIENCES Print– ISSN: 3009 – 7487 Online-ISSN:3009 – 7886 https://jpfs.journals.ekb.eg/ Impact of eco-friendly treatments on managing onion downy mildew Ahmed, M.F.A. 1 , Amin, M.M. 2 and Roshdy, Fatma H. 2 1 Central Lab. of Organic Agriculture (CLOA), Agricultural Research Center, Giza, Egypt. mohamed_faah@yahoo.com https://orcid.org/ 0000-0002-0118-3422 2 Plant Pathology Research Institute, Agricultural Research Center, Giza, Egypt. *Corresponding author: Mohamed F.A. Ahmed mohamed_faah@yahoo.com Received: 1 st December 2024; in revised form: 5 th December 2024/ Accepted: 21 st December 2024/ Published: 31 st December 2024 DOI 10.21608/jpfs.2025.354306.1022 ABSTRACT Onion (Allium cepa L.) is a significant agricultural crop in Egypt, valued for their contributions to both domestic consumption and export markets. However, onion cultivation faces considerable challenges, notably from downy mildew, caused by Peronospora destructor (Berk.) Casp. Serenade ASO 1.34% SC (Bacillus subtilis QST 713 1x10 9 cfu/g) and Tricho Nitro Plus WP (Trichoderma spp. 10 7 spores/ml) were applied at a concentration of 1 L/100 L water/feddan, while Bio Control T34 12% WP (Trichoderma asperellum 10 7 spores/g) and Champ DP 57.6% WG, a copper hydroxide-based fungicide were applied at a concentration of 85 and 180 g/100 L water/feddan respectively to study their effect on onion downy mildew. Champ DP emerging as the most effective solution, significantly reducing the severity of disease by 80.3% and 76.4% after two and three months of application during the 2022-23 and 2023-24 growing seasons. Tricho Nitro Plus followed closely, demonstrating a reduction of 80.2% and 76.3% in disease severity, highlighting its potential as an effective biocide. Notably, all treatments resulted in increasing in onion bulbs yield and enhanced total carbohydrate, total soluble solids and plant enzymes defenses. In conclusion, the application of all treatments, particularly Champ DP and Tricho Nitro Plus, significantly mitigates onion downy mildew, thereby enhancing the yield and quality. This research underscores the potential of integrated management approaches that combine chemical and biological treatments to sustainably address the challenges posed by plant pathogens in onion cultivation, fostering both local food security and agricultural export opportunities in Egypt. Keywords: Onion (Allium cepa L.), Peronospora destructor, bio-fungicide, Champ DP. INTRODUCTION Onion (Allium cepa L.) is the greatest commonly grown Allium specie. Egypt relies heavily on this crop for both domestic and export markets. It contains a high concentration of phytochemicals, specifically medicinal flavonoids (Javadzadeh et al., 2009). Downy mildew caused by Peronospora destructor is a common fungus-like disease associated with onions and other Alliums. Infections generally damage onion plants, although they do induce early leaf dieback and infect the neck of the bulb, providing greens unmarketable and decreasing bulb size and storage quality (Pablo and Colnago, 2011). Downy mildew infection makes crops more sensitive to other diseases (Cook, 2015; Kamel et al., 2017 and Ankita et al., 2019). Humans have recently noticed that the high toxicity of many fungicides might disrupt the delicate balance of ecology and have negative effects on both human health and the environment (Getinet et al., 2024). Research suggests that using antagonistic microorganisms can reduce pathogen inoculum levels and effectively control downy mildew disease in onions without the use of chemicals (Ahmed et al., 2017).