Regular bearing in the apple – Architectural basis for an early diagnosis on the young tree

• We analyze tree architecture at the young stage for 24 apple cultivars.
• We compare these traits with regularity of bearing at the adult stage.
• A few easy-to-collect traits were relevant to characterize the fruiting pattern.
• They are helpful for the grower to adapt training and pruning to the cultivar.
• They contribute to the definition of the apple tree ideotype for regular bearing.

Regular-bearing in fruit trees ensures regular income for the fruit grower and is a main issue for orchard profitability. The relationships between vegetative growth and fruiting have been extensively analyzed on the sexually mature, i.e. adult, tree. However, there are scarce studies on the relationships between growth and flowering of the young tree and the fruiting pattern, i.e. regular vs. alternate bearing, of the adult tree. Our study was developed in the apple, which apart from its economic importance, is likely the most studied fruit species for architecture and fruiting. Twenty-four cultivars with contrasted architectures and fruiting patterns were chosen. Thanks to a principal component analysis, our study compared some architectural traits of these cultivars at the young stage, under minimal pruning and training, and the fruiting pattern of the same cultivars at the adult stage. In the latter case, data were obtained from an independent set of experts from various European regions. Three traits of the young tree were well related to the fruiting pattern of the adult tree: the level of recurrent flowering on the same lateral across consecutive years, i.e. bourse-over-bourse; the cessation of growth of the laterals, i.e. lateral extinction; and the percentage of flowering laterals among all functioning laterals on the one-year-old wood. High values of these three traits were positively related to regular bearing of the adult tree. We discuss the interest to integrate these traits in the definition of an apple tree ideotype for regular bearing that can be useful for an early diagnosis of regular bearing on apple trees in germplasm collections and in progenies.