Development of the grape berry. I. Effects of time of flowering and competition

Abstract

In an experiment on field-grown Vitis vinifera cv. Muscat Gordo Blanco, six times of flowering were established by using early and late developers amongst primary and secondary bunches on winter- and spring-pruned vines. Repeated measurements of the diameters of marked berries and of refraction (¦Brix) of the juice of sampled berries were used to calculate berry volume and weight of solutes per berry. In a second experiment the effect of competition between bunches was tested by thinning. The volume-time curves were similar until 25 days after flowering, after which they diverged markedly. The chief reasons for divergence were the different rates and timing of deceleration during the first growth cycle, and the different lengths of the slow growth phase: berries from late flowers decelerated quickly but had a prolonged lag phase. Some, though not all, of these effects could be attributed to competition between bunches on the same vine. The inceptions of the solute accumulation phase and of the second growth cycle were coincident within treatments. The rates of increase in ¦Brix were uniform between treatments, despite large differences in berry volume increase. Solutes per berry increased linearly for 40 or more days, but at diverse rates that were influenced chiefly by the rate of volume increase in the second growth cycle. In some cases, solutes per berry continued to increase after berries had stopped growing. Temperature summations over the interval from flowering to 17¦Brix were not constant.