Decoding the <i>Penicillium italicum</i> – <i>Citrus</i> Interaction: Untargeted Metabolomics Sheds Light on a Neglected Postharvest Pathogen

<i>Penicillium italicum</i>, the causal agent of citrus blue mold, is a major postharvest pathogen that reduces fruit quality and global citrus productivity. Understanding the molecular basis of infection is crucial to reveal virulence mechanisms, host defense responses, and potential targets for disease control. Here, we investigated the metabolic profile of the<i>Citrus sinensis</i>-<i>P. italicum</i> interaction using mass spectrometry-based metabolomics and desorption electrospray ionization mass spectrometry imaging. Key differential<i>P. italicum</i>-derived metabolites were identified, including 12,13-dehydroprolyltryptophanyldiketopiperazine, deoxybrevianamide E, dehydrodeoxybrevianamide E, deoxyisoaustamide, and brevianamide F. To assess its biological role, brevianamide F was chemically synthesized and tested against citrus-associated endophytes. It selectively inhibited<i>Diaporthe</i> sp., suggesting that<i>P. italicum</i>may utilize this compound as an antimicrobial strategy to modulate the endophytic community during infection. These results provide the first insights into the natural products involved in<i>P. italicum</i>association with citrus and point to potential alternative strategies for controlling blue mold disease.