Dynamics and phases of kiwifruit ( Actinidia deliciosa ) growth curves

We construct a parametric “growth curve”, the average fruit weight versus days since mid bloom, for kiwifruit ( Actinidia deliciosa ). The growth curve takes the form of a double sigmoid multiplied by a “shrinkage curve” (to represent late shrinkage of fruit on the vine before harvest) and the parameters have been fitted satisfactorily to data from four growing seasons, three sites and two treatments. The structure of the curve allows for the estimation of a “change point” at which the acceleration of the fruit weight is minimised. The fruit size at harvest is then shown to be partially determined by the timing of the change point and the fruit weight at that time. The timing of the change point is dependent on the average temperature during the period of rapid initial growth. These results have a potential application in the prediction of mean harvest fruit weight, using information available at an earlier time in the growing season.