South Africa’s apple industry is facing increasing pressure from climate variability and declining winter chill. This study investigated how young apple genotypes perform under these changing conditions, focusing on phenology, tree architecture and the role of rest-breaking agents (RBAs) across different environments in the Western Cape province of South Africa. The study involved a multi-environment trial (MET) across three climatically distinct regions – ranging from low to high winter chilling. Ten apple genotypes, differing in chilling requirements, were evaluated to assess adaptability. All trees were grown under uniform orchard conditions: the same rootstock (M.7 EMLA), central leader training, and standardized planting density. Statistical methods including analysis of variance (ANOVA), the Additive Main effect and Multiplicative Interaction (AMMI) model, genotype + genotype-by-environment (GGE) biplot and discriminant analysis (DA) were used to analyze genotype-by-environment interactions (GEI) and to identify traits critical for environmental adaptation. The results revealed distinct genotypic responses to accumulated heat and chill, which influenced bud break and vegetative traits. RBA application proved especially important in low chill regions, enhancing bud break in higher chill-requiring genotypes. However, RBA effects were inconsistent in high-chill areas and had limited influence on vegetative growth. Most notably, ‘Louterwater Granny Smith’ emerged as a robust genotype, showing low chill requirements, early and reliable bud break, and a favorable response to RBA application – although the genotype is not without management challenges. The findings reinforce the importance of selecting genotypes not only for their performance but also for how well their weaknesses can be mitigated through horticultural practices such as rootstock choice, pruning, growth regulators, or planting density. This work is part of a longer term 8-year project and was carried out in collaboration with Provar, Stellenbosch University and the Agricultural Research Council (ARC), utilizing the Pro-Hort EcoPhysiology Platform (PHEPP), with funding provided by HORTGRO.
Tristan Dorfling won the ISHS Young Minds Award for the best poster presentation at the XIII International Symposium on Integrating Canopy, Rootstock and Environmental Physiology in Orchard Systems in New Zealand in January 2025.
Tristan Dorfling, Provar, Unit 5, Pearl Building, Zandwyk Park, R101, 7646 Western Cape Paarl, South Africa, e-mail: tristan@provar.co.za
The article is available in Chronica Horticulturae