Efecto de la edad del fruto en la intensidad de brotación y floración del limón Eureka

Citriculture is the main horticultural production in Uruguay, with lemon production accounting for 31 % of the national output. Unlike other citrus species, the lemon tree generates reproductive shoots in all its sprouting flushes, which allows for the coexistence of fruits at various developmental stages and facilitates a summer harvest in addition to the winter one. Floral induction in Citrus is regulated by a complex interaction of endogenous and exogenous signals. Endogenously, the fruit exerts a significant inhibitory effect, primarily associated with gibberellins, which repress the expression of genes linked to floral induction and differentiation. Furthermore, fruit presence in the brunch reduces shoot sprouting, thereby restricting the formation of new buds. The main exogenous factors promoting this process are low temperatures and water stress. Given the reflorescent characteristic of the lemon tree, it is essential to elucidate the influence of the fruit’s developmental stage on the regulation of flowering intensity during both spring and summer-autumn sprouting. The objective of this study was to determine the effect of the fruit developmental stage of the 'Eureka' lemon tree on spring and summer-autumn sprouting and subsequent flowering. Specifically, the influence of winter-harvest and summer-harvest fruit was evaluated on these flushing events, as well as the effect of bud position (apical vs lateral). The experiment was conducted in a commercial orchard in San José, using one branch as the experimental unit with 30 replicates per treatment. Four treatments were established: (SF) branches without fruit; (CFi) branches with fruit in Stage III during winter (winter harvest); (CFv) branches with fruit in Stage II in winter and Stage III in summer (summer harvest); and (CFv-R) branches with fruit in Stage II in winter and without fruit in summer. Sprouting and flowering (number of shoots and nodes) were evaluated in spring and summer-autumn, and shoot type and bud position on the branch were identified. Data were analysed using generalised linear mixed models. Results demonstrate that SF branches exhibited the highest sprouting and flowering intensity. Fruit presence significantly reduced both variables. The CFi treatment (fruit in Stage III during the inductive period) significantly reduced flowering and the proportion of reproductive shoots, while simultaneously increasing the proportion of vegetative shoots. Conversely, CFv and CFv-R treatments exerted a more marked inhibition on shoot sprouting; however, considering the flushed nodes, an intermediate proportion of reproductive shoots was recorded. Summer-autumn flushing was minimal; fruit presence almost completely suppressed it, with no shoots in CFv and CFv-R. Only SF displayed flowering, suggesting a persistent inhibitory effect of winter-harvest fruit. In summary, fruit presence has a marked inhibitory effect on sprouting and flowering. This effect seems to be conditioned by the fruit’s developmental stage: fruits in Stage III during the winter induction period were associated with the highest flowering suppression. Conversely, summer-harvest fruits (in Stage II in winter) inhibited spring sprouting more strongly than winter-harvest fruits (in Stage III in winter). No significant effect of bud position was found on spring sprouting and flowering.