Flower scent bouquet variation and bee pollinator visits in Stevia rebaudiana Bertoni (Asteraceae), a source of natural sweeteners

Pollinators provide a key service to both natural and agricultural ecosystems. Little is reported on the pollination chemoecology of Stevia rebaudiana (Asteraceae), a hermaphroditic species producing self-incompatible florets in small corymbs. We investigated the chemistry of volatiles potentially involved in its pollination system. The VOCs emitted by the corymbs of 27 F1 open-pollinated genotypes were collected by solid-phase micro-extraction and analyzed by gas chromatography-mass spectrometry (GC-MS), as well as morphometric data of the genotypes were recorded. Finally, we quantified the abundance of pollinators for each genotype. S. rebaudiana flowers were mainly visited by bees (Apidae and Halictidae), followed by hoverflies (Diptera: Syrphidae). GC-MS indicated that S. rebaudiana was characterized by a complex scent profile with large variability among F1 plants. Discriminant analysis showed that limonene, delta-elemene and bicyclogermacrene were the compounds explaining most of the scent bouquet difference between high attractive (> 40 pollinators/plant) from low attractive pollinator power (< 40 pollinators/plant). Limonene was the most representative VOC among plants that are more attractive to pollinators, while high emissions of delta-elemene and bicyclogermacrene were linked to plants that are less attractive to pollinators. S. rebaudiana morphometric data highlighted that, besides floral VOCs, corymb abundance and size, as well as plant height, may route pollinator visits. Overall, this study adds knowledge on floral phenology and pollinator ecological traits of S. rebaudiana, allowing a deeper understanding of its chemical ecology and pollination.