Tree architecture, flowering and fruiting – thoughts on training, pruning and ecophysiology
Résumé
Training and pruning protocols are developed to improve orchard profitability, especially yield quantity and quality, and regular bearing. This paper gathers two sets of results in the apple. At the whole-tree scale, we showed that the training system efficiently affects fruit quality in a given year, but its effect on regular bearing depends on cultivar. These results together with a common expertise developed in past experiments and in private orchards suggest that there are ‘plastic’ cultivars for which usual pruning and training protocols are able to improve regular bearing, and ‘non-plastic’ cultivars for which alternate bearing is less influenced by pruning and training. At the shoot scale, the relationships between the length of a shoot and the frequency of terminal flowering and fruiting strongly suggest that all relations between vegetative and reproductive growth should clearly distinguish flowering and fruiting. Indeed, flowering appears more genotype-dependent than fruiting. These findings have consequences on the way we prioritize research on tree structure and function. Most ecophysiological studies of sink-source relationships in fruit-trees are strongly influenced by models developed in annuals. They implicitly assume a competitive balance between vegetative growth and fruiting, and strive to achieve high partitioning of carbon to the fruit. In fruit-trees with complex architectures such as the apple, and especially for cultivars with an alternate-bearing pattern, vegetative growth can be completely decoupled from fruit production in the off-year. Our objective would rather be to take into account the uniqueness of the fruit-tree, emphasizing the need for collaborative works between morphologists and eco¬physiologists on the one hand, and geneticists and breeders on the other hand, with research focused on allocation to bud organogenesis and return-bloom which is a prerequisite for fruit production.