Relative proportions of seed, skin and flesh, in ripe berries from Cabernet Sauvignon grapevines grown in a vineyard either well irrigated or under water deficit

Relationships between the fresh mass of seed, skin (exocarp), and flesh (mesocarp) in six different berry size categories, were assessed on ripe fruit from Cabernet Sauvignon grapevines exposed to either High (H), Control (C) or Low (L) water status during post-veraison berry growth in a vineyard. Berries harvested from each treatment were segregated into six mass categories in order to distinguish between changes in fresh mass components associated with general variation in berry size (on well-watered grapevines), and those associated with berry size differences due to water stress. Berry fresh mass across all treatments ranged from about 0.4 to 2.0 g. Fresh mass components for both H and C berries comprised approximately 5% seed, 15% skin, and 80% flesh, regardless of variation in berry size, although there was some increase in seed mass relative to whole-berry fresh mass in larger berries. Berry growth (as inferred from fresh mass at harvest) was much less sensitive to water deficit than published reports for grapevine shoot growth. Midday leaf water potentials around –1.20 MPa (Control) were not sufficient to inhibit berry growth. However, midday water potentials around –1.50 MPa (Low water status) inhibited berry growth by 13–18% of that attained by grapevines grown at high water status (i.e. treatment H where midday leaf water potentials remained around –1.00 MPa). Inhibition of berry growth by water deficit was attributed almost exclusively to reduced growth of mesocarp tissues (for most berry size categories). Water deficit thus increased the proportion of whole-berry fresh mass represented by seeds and skin (for most berry size categories). Changes in those proportions due to irrigation treatments exceeded differences associated with general (non-stress) variation in whole-berry fresh mass. Excluding adverse environmental impacts on whole-berry fresh mass, our results point to a limited role for variation in berry size per se as a factor determining the solute concentration of juice or wine derived from different sized fruit. By implication, and for all categories of whole-berry fresh mass represented here, late season water deficit can result in ripe fruit with more skin and seed tissues (relative to whole-berry fresh mass) compared with well-watered control fruit.