Grape Berry cv. Shiraz Epicuticular Wax and Transpiration during Ripening and Preharvest Weight Loss

Abstract

Preharvest weight loss of Vitis vinifera L. cv. Shiraz berries may be the result of cuticle disruption leading to high transpiration rates relative to earlier stages of ripening. Scanning electron microscopy showed very few but functional stomata on young berries and wax-filled stomata on older berries and, aside from slight cracks along the stomatal protuberance, did not reveal any fissures in the surface of berries that may lead to increased transpiration rates. Preveraison berry epicuticular wax platelets were defined and intricate, while postveraison and shriveled berry surfaces had large areas of amorphous waxes. Postveraison, the area of amorphous wax relative to intricate wax was not correlated with berry age or degree of shrivel. Extraction of surface waxes revealed that total wax on a surface-area basis decreased during veraison then remained stable as the berries ripened and entered the weight-loss phase. Berry transpiration, estimated from loss of fresh weight of detached berries over time, during this final shriveled phase was 16% of the preveraison rate on a per berry basis. Nevertheless, berry transpiration could account for an average 15 mg loss in fresh weight per berry per day. We conclude that weight loss during late ripening of Shiraz berries was not the result of cuticle disruption or high transpiration rates alone. It is hypothesized that decreased vascular flow of water into the berry combined with continued transpiration leads to the weight loss.