Evaluation of Some Biocontrol Agents to Control Postharvest Disease of Onion Crop

Abstract

This study evaluated the field application of biological control agents (Trichoderma harzianum and Chaetomium globosum) (30×10⁶ CFU/mL, applied as 1 L/100 L) and inorganic salts (calcium carbonate, at 50, 70, and 90 mM) to manage black mold infection and preserve bulb quality during ambient storage. Field trials were conducted over two consecutive winter growing seasons (2022/2023 and 2023/2024) at the El-Sadat experimental farm, Menoufia Governorate, Egypt, on onion cultivar Giza 6. Treatments were applied as a 10-minute seedling dip prior to transplanting, followed by bi-weekly foliar applications (seven applications in total) starting mid-January. Results demonstrated that biological agents significantly reduced disease incidence and severity. T. harzianum achieved the highest efficacy in reducing infection rate (44.7% efficacy), while C. globosum suppressed overall disease severity most effectively (44% efficacy). Calcium carbonate treatments, particularly at 90 mM, markedly suppressed bulb decay (83.1% efficacy) and reduced total weight loss (63.8% efficacy compared to control). Furthermore, treatments enhanced biochemical defenses, significantly elevating peroxidase and polyphenol oxidase enzyme activities, as well as preserving total soluble solids (TSS) and bulb firmness throughout storage. These findings highlight the potential of combining biocontrol agents and calcium applications as an effective integrated management strategy against black mold and post-harvest onion decay.