Background and Aims: Cell death in the mesocarp of Shiraz berries has been correlated with berry mass loss that occurs late in ripening and can be linked to berry composition. The current techniques to assess the level of berry cell disruption are time-consuming and can give only relative measures. Here we test if electrical impedance of the berry, which is a function of the state of cells within, can be used to detect the loss of cell vitality. Methods and Results: Shiraz berries (774 berries) from two locations (one of them over two seasons) from veraison to harvest were studied. Electrical impedance spectroscopy was performed between 100 Hz and 1 or 2 MHz of alternating current across the berry, while for each berry proportion living tissue was estimated with fluorescein diacetate. The results indicated that, from veraison to the onset of cell death, berry impedance follows the accumulation of TSS. Thereafter, impedance decreases proportionally to the extent of berry cell death. Conclusions: Changes in cell vitality of the Shiraz grape berry can be objectively determined through impedance spectroscopy. The measurements also indicate that cell membranes, although becoming leaky, may still remain intact. Significance of the Study: Impedance spectroscopy as applied to the grape berry has demonstrated a promising application for measuring berry composition.
Background and Aim: High temperature stress has been linked to detrimental effects on berry composition during ripening. This study aimed to assess the impact of an evaporative cooling system located inside the grapevine canopy to mitigate extreme temperature effects on grape berry composition during ripening. Methods and Results: During three seasons (2012 to 2015), an intra-canopy sprinkler system at the bunch zone was tested on Cabernet Sauvignon vines. The system cyclically sprayed (20 s/10 min) for an air temperature above 38°C, cooling the air inside the canopy by 3 to 5°C. This is in agreement with an air cooling simulation model. The relative humidity in the canopy also increased in the sprinkler-cooled canopy. No differences were detected in TSS, although sugar per berry was significantly higher in treated vines because of increased berry mass. There was a tendency for higher anthocyanins and phenolic substances per berry in cooled berries measured from two seasons and higher concentration of anthocyanins in wine from cooled fruit measured only in one season. We define indices that can be used to assess the efficiency of sprinkler cooling and to demonstrate the high efficiency of intra-canopy sprinklers compared to other systems. Conclusion: Despite cooling operating only over a small duration of the ripening period, the increased berry mass indicates that high temperature, even for a short period, has a profound effect on berry growth. Other berry compositional properties and wine, however, were not impacted. Significance of Study: This research demonstrates the potential of an efficient intra-canopy sprinkler system to reduce heat stress during ripening.
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