To what extent does vine balance actually drive fruit composition?

Abstract

Context and purpose of the study ‐ Vine balance is a concept describing the relationship between carbon assimilation (usually estimated using a measure of vine vigour, e.g. pruning weight) and its utilisation for fruit production (usually estimated using harvest yield). Manipulating vine balance through leaf area or crop load adjustments affects the proportion of the vine’s total carbohydrate production required to mature the fruit. It is commonly considered that composition of the berry, and resulting wine, is strongly affected by vine balance.

Material and methods – Field manipulations of vine balance were replicated in three contrasting viticultural regions of Australia, Hilltops, Murray Valley and Langhorne Creek, over three seasons. The manipulations were early defoliation (pre‐capfall), late defoliation (pre‐véraison) and 50% crop removal (pre‐véraison). Fruit were sampled prior to a treatment being applied and then at approximately two‐ week intervals until harvest, where small lot wines were made from each field replicate. The fruit samples were analysed for maturity, basic composition and the expression of key genes that regulate anthocyanin and tannin formation. In addition, the effect of defoliation was simulated, without changing bunch environment, by enclosing whole vines in chambers and supplying them with low CO2 air to reduce photosynthesis.

Results – Changing vine balance consistently altered the rate of ripening, but did not correlate with treatment effects on fruit composition, where they occurred. Late defoliation extended the maturation period, but reduced total anthocyanin content. Crop removal shortened the maturation period, but had little effect on the fruit. Interestingly, early defoliation had no clear effect on vine balance, but resulted in both increased anthocyanin and increased tannin content. The chamber experiment also extended the maturation period, but had no effect on the relationship between sugar and anthocyanins. Overall, there was no conclusive evidence that the changes in vine balance achieved had any significant effect on fruit or wine composition when fruit were harvested at the same sugar ripenesss.