Chilling and heat requirements of apple cultivars: Future perspectives in a global climate change context

Abstract

Climate change is affecting fruit tree dormancy progression around the world. Temperature increase during winter could hinder the attainment of the climatic requirements that are needed to have a correct dormancy release. In this context, knowing the chill accumulation needed by each cultivar is essential to make correct decisions on the cultivar selection for each region. Searching for new tools and alternatives is also basic to adapt current cultivars to this new scenario. For this purpose, chill and heat requirements have been assessed for ten relevant apple cultivars using the forcing methodology and their correlation with full bloom date. Bud break response at different chilling accumulations has been modelled with logistic curves. In this work, a climatic study of a highly productive apple region in a Mediterranean agroecosystem revealed a decrease in chill accumulation during the last decade. In this context, cultivars whose chill requirements were below 40 chill portions (‘Lory®’, ‘Pink Lady®’, ‘Luiza’ and ‘Galy®’) are highly recommended for the future, showing a high bud break percentage at low chilling accumulation. Other cultivars currently grown in the region (‘Gala’ or ‘Fuji’) could present problems in the most critical climate change scenarios. Rootstocks did not show any influence on the modulation of chilling requirements. Furthermore, chilling, rather than heat requirement, was the most important parameter determining the flowering date. This study will help growers in decision making for the selection of the most appropriate cultivar under future climatic conditions, thus avoiding problems related with a non-optimal chill accumulation.