Green Mold of Citrus: Recent Insights into Penicillium digitatum Pathogenicity and Biological Control Strategies

P. digitatum, the causal agent of citrus green mold, remains the most destructive postharvest pathogen of citrus worldwide. Recent advances have greatly expanded our understanding of the molecular dialogue between P. digitatum and citrus hosts, revealing coordinated virulence strategies involving cell wall-degrading enzymes, major facilitator superfamily transporters, transcription factors, and secondary metabolism, alongside host defenses mediated by phytohormones and specialized metabolites. This review integrates genomic, transcriptomic, metabolomic, and functional genetic discoveries, including CRISPR/Cas9 and Agrobacterium tumefaciens-mediated transformation, which have accelerated the characterization of fungal pathogenicity and host resistance. We further assess biological control as a sustainable alternative to chemical fungicides, emphasizing complementary mechanisms such as niche competition, antibiosis, volatile organic compound (VOC) production, biofilm formation, iron sequestration, lipopeptide synthesis, and induction of host defenses. In addition, we highlight microbiome-informed strategies and the design of synthetic microbial communities (SynComs) as promising next-generation approaches to enhance efficacy, stability, and ecological resilience in citrus postharvest disease management.