Fruit Quality Regulation in Passion Fruit (Passiflora edulis): Biological Mechanisms, Omics Evidence, and Opportunities for Biological Intervention

Passion fruit (Passiflora edulis) quality is defined by integrated sensory and nutritional traits, including sugar–acid balance, volatile organic compounds (VOCs), pigment-related attributes, and bioactive compounds such as ascorbic acid and phenolics. These traits emerge from coordinated regulation of carbon allocation, mineral nutrition, ripening metabolism, and stress- and defense-related signaling pathways, which are strongly modulated by environmental conditions. Sustainable biological inputs are increasingly explored as tools to influence these regulatory networks; however, evidence linking such interventions to reproducible fruit quality outcomes in Passiflora remains fragmented. This review first synthesizes current knowledge on the physiological, biochemical, and molecular mechanisms underlying passion fruit quality formation and maintenance, and then discusses how biofertilizers; microbial inoculants (including plant growth-promoting rhizobacteria—PGPR and arbuscular mycorrhizal fungi—AMF); fungal-derived elicitors such as chitosan and chitooligosaccharides; and complementary postharvest biological strategies may modulate these processes. Emphasis is placed on traits beyond yield, including sugar–acid balance, aroma and VOC profiles, color, nutritional quality, texture, and shelf life. By integrating genomics, transcriptomics, metabolomics, proteomics, and microbiome-based evidence, we examine how environmental modulation and key signaling pathways intersect with metabolic networks underlying fruit quality. Available studies indicate that responses to biological inputs are context-dependent and often non-linear. Key knowledge gaps and priorities for mechanism-informed sustainable management of passion fruit quality are identified.