Canopy age of Vitis vinifera L. cv. Shiraz derived from the modelling of logistic shoot growth and/or plastochron index

Abstract

Knowledge about grapevine leaf and canopy age is relevant when studying plant reaction to the environment. For example, in studies about source:sink relationships in the grapevine “quality of the source” with regard to leaf age and pigment composition may play an even more important role than source quantity (i.e. as determined by leaf area:fruit mass ratios). In this study, shoot growth and leaf plastochron index (PI) measurements were performed over three growing seasons in a Shiraz vineyard. The main objective was to determine relations between different shoot growth parameters and to devise a way to simplify leaf and canopy chronological age determination. Logistical growth curves were fitted to shoot growth and PI datasets and development rates calculated. Considerable seasonal differences were noted; this could be related to climatic and soil water status variation. A method was proposed to infer leaf chronological age by calculating date of leaf formation from logistic fit equation derived from the ‘PI:date after budburst’ relationship. This approach incorporated changes in shoot plastochron duration during the growing season. Mean chronological leaf age, calculated using this method plotted against mean leaf PI values for all seasons, showed very small seasonal differences between these parameters. This suggested that leaf PI measurements could be useful as a canopy age estimator throughout the growing season. Some perspectives on measurement of PI in grapevine canopies are discussed, also incorporating complications that may arise due to shoot topping and secondary shoot growth in commercial vineyards.