Modelling variety-dependent dynamics of soluble solids and water in berries ofVitis vinifera

Abstract

Background and Aims: We modelled the dynamics of soluble solids, largely sugars, and water in 12 Vitis vinifera varieties. Emphasis was placed on maximum concentration of soluble solids (S(max)) and time of maturity for their viticultural importance.Methods and Results: We measured the concentration of soluble solids and water at weekly intervals during berry ripening. The dynamics of concentration of soluble solids was characterised with a sigmoid model, whereas water concentration was characterised with a concentration-response type curve. Scaling exponents for soluble solids (alpha(s)) and water (alpha(w)) were calculated as the slope of the log-log regression between amount of soluble solids or water per berry and berry fresh mass. S(max) ranged from 27.1% in Shiraz to 21.2% in Riesling, was associated with both alpha(w) and alpha(s), and was largely unrelated to source size (leaf area, pruning weight, light interception), source activity (stomatal conductance), sink size (yield components) and source : sink ratios. The time of maturity ranged from 26 January in Verdelho to 27 February in Crimson Seedless, and was an inverse function of the rate of change in concentration of soluble solids, which was in turn a direct function of stomatal conductance.Conclusions: Traits related to carbon assimilation influenced time of maturity, but their link with maximum concentration of soluble solids in berries was not evident.Significance of the Study: Quantitative models of accumulation of soluble solids are presented that provide a baseline for comparisons among varieties.