A spatial perspective on flowering in cauliflorous cacao: architecture defines flower cushion location, not its early activity.

Abstract

Background and aims: Theobroma cacao L., a tropical sciaphilous tree, exhibits cauliflory, with persistent flowering sites known as flower cushions. Cushions develop from floral buds located at the axils of leaves or cataphylls. They can sustain recurrent flowering and contribute to the tree's fruit production throughout its lifespan. However, factors influencing their formation and flowering activity remain poorly understood.

Methods: Architectural and geometrical measurements, combined with weekly monitoring of flowering activity at the node scale, were conducted on plagiotropic branches of two cacao genotypes under medium and heavy shade. We investigated how architecture and geometry influence cushion formation, frequency and duration of flowering episodes, and synchrony of flowering among cushions at different scales.

Key results: Flower cushions developed once a flush (growth unit) had reached a specific ontogenetic age, defined by its position along the shoot (axis). The probability of flower cushion formation was then primarily determined by the node's (phytomer) position within the flush and its basal diameter. Heavy shade (90% light reduction) greatly limited cushion formation, irrespective of the architectural traits or growth characteristics of the node, flush or shoot. In contrast, the temporal activity of the flower cushions was not related to architectural or geometrical factors, and flowering occurred with moderate synchrony at the growth unit, axis, and branch scales.

Conclusions: These findings indicate the dual importance of shoot ontogeny and node-specific traits in flower cushion formation in this cauliflorous species. They also demonstrate the overall negative influence of heavy shade on flower cushion development, and the absence of architectural constraints on the flowering activity of cushions during the tree's first reproductive phase. Further analyses are needed to better understand the hormonal and carbohydrate regulation of flowering and fruiting in productive trees of this cauliflorous species.