Abstract:

On-tree storage is an effective strategy to keep citrus fruits fresh on tree，which can prolong harvesting season and relieve the pressure of fruit sale in a limited period. However，little knowledge is available for implementation of on-tree storage of ponkan fruits. In the present study，exogenous spermidine（Spd）was supplied to‘New Line 3’ponkan（Citrus reticulata）to investigate the role of Spd in lessening fruit dropping during overwinter on-tree storage and to understand the potential underlying mechanisms. Our results demonstrated that application of 1 mmol · L-1 Spd had negligible effects on influencing fruit quality，while noticeably decreased the rate of fruit dropping. Meanwhile，exogenous supply of Spd suppressed ROS production in the fruit abscission zone，concurrent with significant reduction of the activities and expression levels of cellulase（CX），polygalacturonase（PG）and pectin esterase（PME），three key enzymes associated with cell wall degradation. This leads to retardation of cell wall degradation and impairment of formation of abscission zone. Taken together，our data revealed that exogenous application of Spd could delay the formation of abscission zones in the fruits，allowing it to be used possibly for keeping ponkan on-tree fruits fresh overwinter.

Key words: ponkan, Citrus reticulata, on-tree storage, spermidine, abscission zone