Determination of Target Crop Loads for Maximising Fruit Quality and Return Bloom in Several Apple Cultivars

Abstract

In apple (Malus domestica), the level and timing of crop load have a major impact on the final fruit size and can also play a role in optimising internal fruit quality. Ideal crop loads vary with cultivar, but very few cultivars have recommended crop load targets that consider the effect of crop load on both return bloom and fruit quality. To address this issue, studies examining a range of crop loads and thinning times were undertaken on several apple cultivars. Return bloom and multiple fruit quality parameters were examined. The results of these studies demonstrate positive effects for early thinning, not only on fruit size but also on firmness and soluble solids content. Early-thinned fruit showed higher sugar levels than late-thinned fruit. Previously undemonstrated positive relationships between fruit sugar content and weight and between fruit firmness and weight in both ‘Fuji’ and ‘Delicious’, as well as between fruit sugar content and fruit firmness in ‘Delicious’, indicate that early thinning is a valuable tool in improving fruit quality. The current target crop load recommendations of 4–6 fruit cm−2 trunk cross-sectional area (TCSA) for ‘Fuji’ and 2–4 fruit cm−2 TCSA for ‘Delicious’ are confirmed by this study. New recommendations are proposed for the other cultivars in this study taking into account the impact of crop load on both fruit quality and return bloom. Both ‘Pink Lady’ and ‘Gala’ can support crop loads of up to eight fruit cm−2 TCSA without impacting return bloom, but fruit quality is compromised; hence, lower targets in the range of 4–6 fruit cm−2 TCSA are recommended. Large fruit size and good return bloom can be maintained in ‘Jonagold’ at crop loads of eight fruit cm−2 TCSA, while crop loads of four fruit cm−2 TCSA are suggested for ‘Braeburn’ to sustain regular bearing and good fruit size.