Abstract
Botrytis umbel blight caused by Botrytis allii is a major disease that attacks onion crop. In vitro, Trichoderma viride,
Penicillium chrysogenum, and Saccharomyces cerevisiae and extract of bitter apple fruits (Citrullus colocynthis) showed
antagonistic effect and inhibited the mycelial growth of B. allii. Gas chromatography–mass spectrometry (GC-MS)
analysis of bitter apple fruits showed the existence of 37 compounds and their derivatives. Among them, 10
compounds constituted 58.66% of the total analyses. Greenhouse experiment approved that the extract of bitter
apple fruits was the most effective in reducing disease incidence and severity, followed by P. chrysogenum, when
they were applied 2 days pre-inoculation with the pathogen. All treatments significantly increased the total
phenolic contents than the untreated control, but the highest increase was obtained when S. cerevisiae and P.
chrysogenum were applied. A positive correlation was found between the activity of bioagents and improvement
of peroxidase and phenylalanine ammonia-lyase enzymes in onion plants to resist infection with the pathogen. P.
chrysogenum caused the highest increase in polyphenoloxidase activity in infected onion plants, while S. cerevisiae
showed the lowest level of this enzyme. The study approved that application of the bioagents not only protected
the onions against Botrytis disease but also enhanced the content of antioxidant compounds in onions. This
encourages the application of such preparations to manage the production of onion crop, especially in the
organic farming that bans the application of any chemicals.