New Trichoderma Strains Suppress Blue Mold in Oranges by Damaging the Cell Membrane of Penicillium italicum and Enhancing Both Enzymatic and Non-Enzymatic Defense Mechanisms in Orange Fruits

Abstract

Blue mold disease, caused by Penicillium italicum (P. italicum), presents a significant challenge to orange fruits (Citrus sinensis L.) and other citrus crops globally. Biological control, particularly Trichoderma species, offers a promising alternative to synthetic fungicides. Therefore, this study aimed to isolate, identify, and evaluate the antagonistic activities of two Trichoderma isolates against P. italicum. These isolates were molecularly identified and assigned accession numbers PP002254 and PP002272, respectively. Both isolates demonstrated significant antifungal activity in dual culture assays. Moreover, the culture filtrates (CFs) of Trichoderma longibrachiatum PP002254 and Trichoderma harzianum PP002272 suppressed the mycelial growth of P. italicum by 77.22% and 71.66%, respectively. Additionally, CFs reduced the severity of blue mold on orange fruits by 26.85% and 53.81%, compared to 100% in the control group. Scanning electron microscopy revealed that treated P. italicum hyphae were shrunken and disfigured. Enzyme activities (catalase, peroxidase, polyphenol oxidase, and phenylalanine ammonia-lyase) in treated oranges increased, along with total soluble phenolics and flavonoids. Conversely, malondialdehyde (MDA) levels decreased in treated fruits. These findings suggest that T. longibrachiatum PP002254 and T. harzianum PP002272 could be effective biocontrol agents for managing blue mold and other citrus postharvest diseases.