Melatonin treatment enhanced disease resistance against Alternaria alternata of ‘Korla’ fragrant pear fruit via inhibiting cell wall degradation

Postharvest ‘Korla’ fragrant pears are threatened by Alternaria rot, which impacts storage quality and shelf life. This study explored how melatonin (MT) influences the black spot disease caused by Alternaria alternata ( A. alternata ) of ‘Korla’ fragrant pears, focusing on its effects on cell wall degradation. The results demonstrated that 0.20 mmol L -1 MT treatment significantly reduced lesion diameter and disease index, which were 10.5% and 17.4% lower than those of the control ( p < 0.05). Meanwhile, MT treatment maintained pulp firmness and protected the cuticle in cells, promoted callose deposition, suppressed the activities of cell wall-degrading enzymes including polygalacturonase (PG), pectin methylesterase (PME), cellulase, β-Galactosidase (β-Gal), pectin lyase (PL), and xyloglucan endotransglycosylase (XET), and downregulated the transcription levels of PbPG1 , PbPME20 , PbCEL5 , Pbβ-Gal3 and PbXTH23 , thereby suppressing the increase of water-soluble pectin (WSP), maintaining higher contents of insoluble protopectin (ISP), covalent binding pectin (CSP), cellulose and hemicellulose, delaying cell wall polysaccharides disassembly, and preserving cell wall integrity in pear fruit during storage. These findings indicated that modulating cell wall degradation acts as a vital function in the disease resistance of MT-treated ‘Korla’ fragrant pear fruit.