Comparison of two models for the prediction of rest completion in peaches

Abstract

Phenological and climatic data were collected from nectarine orchards containing the cultivars ‘Sunlite’, ‘Flavortop’ and ‘Fantasia’, growing in six climatically divergent areas in the Western Cape, South Africa. Shoots were forced at 25°C and bud volumes measured in order to develop an index of when the winter chilling requirement for each cultivar in each area had been satisfied. Flower bud break gave the only consistent indication of when the chilling requirement had been satisifed and 10% flower bud break after 14 days at 25°C was adopted as the end of rest index. The ‘dynamic’ rest completion prediction model was considerably more accurate than the currently used ‘Utah’ model, for estimating the rest requirement of the nectarine cultivars ‘Sunlite’, ‘Flavortop’ and ‘Fantasia’. The ‘dynamic’ model not only takes into account the positive effect of cool temperatures and negative effect of high temperatures on rest completion that the ‘Utah’ model does, but also the positive effect of moderate temperatures and the fact that chilling negation is subject to time constraints. The cultivars tested required about 33, 41 and 41 ‘dynamic’ portions of chilling respectively, followed by an average of 2000 ± 1067 degree growing hours above a 10°C base temperature in order to reach full bloom in spring. Vegetative bud break was enhanced in the colder locations, while reproductive development was better in the warmer locations.