Pre-harvest spray of oligochitosan induced the resistance of harvested navel oranges to anthracnose during ambient temperature storage

• Pre-harvest oligochitosan spray.
• The resistance of orange to Colletotrichum gloeosporioides was significantly enhanced.
• HRGP contents were increased and protopectin degradation was inhibited.
• The activities of defense enzymes (PAL, POD, and chitinase) were increased.
• Oligochitosan spray may be a treatment for the post-harvest control of anthracnose.

In this study, the ability of pre-harvest oligochitosan spray to control Colletotrichum gloeosporioides of navel orange during ambient temperature storage was examined. Navel orange trees were sprayed thrice with oligochitosan (15 g L−1 water) after physiological fruit drop. Results indicated that disease incidence and lesion diameter were lower in oligochitosan-treated fruit compared with the respective control. The inhibitory effects of volatiles in navel orange rind on the spore germination of C. gloeosporioides were significantly enhanced in the treated fruit compared with the control. Biochemical evaluations revealed that the contents of hydroxyproline-rich glycoprotein were increased. Protopectin degradation was delayed during storage. In addition, the activities of defense-related enzymes, including pectin methylesterase, peroxidase, chitinase, and phenylalanine ammonia-lyase, were increased in oligochitosan-treated navel orange fruit rinds. Our results suggested that pre-harvest oligochitosan spray can be a potential alternative to conventional control methods to prevent post-harvest anthracnose in navel orange.

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