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

¹ Cooperative Research Centre for Viticulture, PO Box 154, Glen Osmond, SA 5064, AustraliaNational Wine and Grape Industry Centre, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, Australia
² Monash Micro Imaging, School of Biological Sciences, Monash University, PO Box 18, Clayton, Victoria 3800, Australia
³ CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia
⁴ National Wine and Grape Industry Centre, Charles Sturt University, Locked Bag 588, Wagga Wagga, NSW 2678, AustraliaWashington State University, Irrigated Agriculture Research and Extension Center, Prosser, WA 99350 USA.

email suzy.rogiers{at}agric.nsw.gov.au

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.

Note:
Acknowledgments: This research was supported by the Commonwealth Cooperative Research Centre Program and conducted through the CRC for Viticulture with support from Australia’s grapegrowers and winemakers through their investment body the Grape and Wine Research and Development Corporation, with matching funds from the federal government. We thank Paul Kriedemann for helpful discussions during the course of this study. Technical assistance by Robert Lamont is also gratefully acknowledged. Thanks to the Charles Sturt Winery for permitting fruit sampling and to the vineyard staff for vine maintenance.

Key words: Vitis vinifera, berry, shrivel, transpiration

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