Ascorbic acid and melatonin synergistically maintain postharvest guava quality by regulating cell wall, antioxidant, and transcriptomic pathways.

Guava is highly perishable with postharvest decay and senescence, limiting storage and marketability. This study examined the synergistic regulatory effects of combined AsA + MT (AM) treatment on preserving 'Pearl' guava. Systematic analyses assessed fruit storage quality, antioxidant activity, and cell wall metabolism during storage. AM treatment markedly reduced browning and weight loss, maintained firmness, soluble solids, and vitamin C, and slowed titratable acidity decline. Mechanistically, AM enhanced antioxidant enzymes (SOD, POD, APX, CAT), reduced malondialdehyde accumulation and alleviated oxidative damage. It also suppressed cell wall-degrading enzymes (PG, PME, CX, β-GAL), stabilizing protopectin and cellulose to delay degradation. Transcriptomic and WGCNA analyses revealed modulation of genes linked to antioxidant defense and cell wall metabolism with ERF, NAC, and bHLH transcription factors identified as key regulators. Overall AM synergistically preserved guava quality by coordinating antioxidant and cell wall regulation, offering a theoretical and practical basis for sustainable tropical fruit preservation.