Cell death in Vitis vinifera L. berries late in ripening and berry shrinkage (loss of mass) can decrease yield and reduce grape quality in cultivars such as Cabernet Sauvignon, Merlot, and especially Shiraz. Techniques to ameliorate effects of cell death and berry shrinkage are limited. Pinolene and kaolin are two types of film-forming antitranspirants applied to plants to reduce water loss. If these antitranspirants create a water impermeable coating, they may also restrict gas exchange, exacerbating hypoxia associated with cell death in grape berries. This study aimed to identify the effects on berry physiology during ripening of kaolin and pinolene coatings on Shiraz and Grenache bunches.

Kaolin (6% w/w), pinolene (1% w/w) and water (control) were sprayed on Shiraz and Grenache bunches (2019-2020, Waite campus University of Adelaide) during ripening every 7 to 15 days. Change in berry mass, cell vitality, internal oxygen concentration, ethanol accumulation and bunch and canopy temperature were recorded.

Grenache berries had almost no shrinkage and no cell death during development contrasting to continuous decline in berry mass and cell vitality in Shiraz berries from 85 days after anthesis. Kaolin had no effects on berry properties.  Pinolene reduced loss of berry mass in Shiraz and slightly increased berry mass in Grenache, leading to lower sugar concentrations in both cultivars. There was no effect of pinolene on berry oxygen concentration or cell vitality since both declined similarly to controls. There was an exponential increase in berry ethanol concentration with increasing mean daily temperature. Berry ethanol concentration for Grenache was much lower than for Shiraz under similar temperature conditions. There was no effect of treatments on berry ethanol concentrations.

Pinolene decreased berry shrinkage and prevented high sugar concentration presumably by reducing transpiration without impacting sugar content. It was surprising that this compound could decrease water loss without apparently affecting internal oxygen concentration in the berry. Ethanol accumulation during berry ripening could be a causative factor of cell death or is closely associated with it. Temperature may decrease berry vitality by accelerating respiration which leads to anoxia and high ethanol production.

Poster presented at Macrowine virtual (June 23-30, 2021)

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