The costs of reproduction in plants: a novel approach to study irregular bearing of fruit crops

Irregular bearing is a major issue limiting productivity of temperate and tropical fruit crops. It is generally studied through the effects of fruit production in one year on flowering and fruit production in the following year, involving classical nutritional and/or hormonal hypotheses. As shown in various species, especially in the apple, there are strong reciprocal relationships between vegetative and reproductive growth, not only in a same year but also from one year to the other. These relationships are then a key point to understand irregular bearing. The effects of flowering and fruiting on the subsequent vegetative growth were investigated during two growing cycles on two irregular mango cultivars. Vegetative growth was quantified by the biomass and leaf area of new axes, assessed by allometric relationships. Negative relationships between fruit production and the subsequent vegetative growth were evidenced at the tree, scaffold branch and growth unit levels, with differences between the two cultivars. On the basis of these results, a novel approach is presented to study in a more comprehensive way the mechanisms involved in irregular bearing. It relies on the conceptual framework of the costs of reproduction in plants, originally developed in evolutionary ecology. The hypothesis is that compromises are necessary to allocate plant resources among three vital functions, namely growth, reproduction and defence, in order to maximize the reproductive success during the whole life span, and not during only one production cycle. We discuss the interest of this concept to study irregular bearing. (Résumé d'auteur