Quantifying phenotypic plasticity of berry traits using an allometric-type approach: A case study on anthocyanins and sugars in berries of Cabernet Sauvignon

Abstract

In this paper we advance a novel allometric-type approach to quantify the stability of key berry traits viz. anthocyanins and sugars. To test the concept, we used data from Cabernet Sauvignon grown in a hot environment of South Australia. Sources of variation in berry traits included water supply, fruit load, seasonal conditions and their interactions. Anthocyanins and sugars were measured in berry samples taken 7–8 times between veraison and harvest. Rates and durations of accumulation of anthocyanins and sugars per berry were derived from a bi-linear model between amount of compound and thermal time. We develop a framework based on ‘α’ a parameter representing the slope of the regression between rate and duration in a log-log scale. This relationship accommodates three conditions viz. (a) potentially plastic, rate-driven trait (α –1), (b) potentially plastic, duration-driven trait (α < –1), and (c) a stable trait, whereby variation in rate and variation in duration cancel each other (α = –1). Under our experimental conditions, amount of anthocyanins (range of variation 148%) was more plastic than amount of sugars per berry (range of variation 37%). The slope α captured the differential plasticity of these traits: α was significantly greater than –1 for anthocyanins and statistically undistinguishable from –1 for sugars. The rate-dominated accumulation of anthocyanins explained the relatively large variation in this constituent whereas the tightly coupled, inverse relationship between duration and rate (α –1) explained the relative stability of sugars per berry. We conclude that our allometric-type relationship between rate and duration allows for the quantification of cultivar-environment specific plasticity of important berry traits.