Grape berry transpiration: determinant factors, developmental changes, and influences on berry ripening

Genetically diverse Vitis cultivars were used to investigate developmental changes and factors determining grape berry transpiration. Vapor pressure deficit was the main determinant driving berry transpiration and caused daily fluctuations of transpiration rate. Berries of various cultivars shared similar developmental patterns of transpiration and cuticular conductance. The transpiration rate berry^-1 and, to a lesser extent, the cuticular conductance, peaked when the skin color of berries was red/purple (about 13 °Brix) and then declined with further ripening. The positive linear relationship between berry transpiration rate and surface area weakened after berries matured, due to a decline in cuticular conductance during late ripening. Differences among cultivars also existed. Vitis labruscana 'Concord' berries consistently had much lower cuticular conductance than V. vinifera 'Merlot' and 'Syrah' berries. Across 10 cultivars, berry transpiration accounted for a daily loss of 2 to 3% of berry fresh weight after maturation (overripe). Forced reductions in berry transpiration decreased the solute accumulation rate yet increased cracking frequency. These results showed that berry transpiration was determined by both external conditions (vapor pressure deficit) and cultivar-specific internal factors (primarily berry surface area and cuticular conductance). Moreover, berry transpiration facilitated ripening, likely by discharging excess phloem-imported water.