Genotype and environment effects on sunflower nectar and their relationships to crop pollination

Authors: Prasifka, Jarrad; Yoshimura Ferguso, Mary; Fugate, Karen

Submitted to: Journal of Pollination Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2023
Publication Date: 2/16/2023
Citation: Prasifka, J.R., Yoshimura Ferguson, M.E., Fugate, K.K. 2023. Genotype and environment effects on sunflower nectar and their relationships to crop pollination. Journal of Pollination Ecology. 33(4):54-63. https://doi.org/10.26786/1920-7603(2023)719.
DOI: https://doi.org/10.26786/1920-7603(2023)719

Interpretive Summary: The nectar reward a sunflower provides to bees depends on the type or ‘variety’ and the conditions, especially temperature, in which the crop grows. To better understand how pollinators choose which sunflowers to visit, several sunflower varieties were grown under different temperatures and nectar collected from the flowers. Separate experiments also looked at how mesh bags (used to keep bees from moving pollen in breeding or insect research) change the nectar rewards available to bees. In general, much more nectar was found when plants were grown in warmer temperatures, but not all varieties showed the same pattern. The different temperatures in which plants were grown caused only small changes in nectar concentration or the types of sugars found in nectar. Sunflower plants covered with mesh bags contained much more nectar, and far more bees visited these plants when bags were removed. Even though not all varieties react to temperature changes in the same way, plant breeders can still create sunflowers that provide more nectar to bees. Because of how mesh bags change nectar rewards, research on sunflower pollination should avoid using these bags when possible.

Technical Abstract: Whether caused by genotype (G) or environment (E), floral trait variation has consequences for plants and their pollinators. Cultivated sunflower is a model system to explore this idea; though sunflowers are bred to self-pollinate, benefits of pollination by bees remain substantial. To better understand sunflower-pollinator interactions, experiments were conducted to: (i) examine genotype and environment effects on nectar quantity and quality under controlled conditions, and (ii) assess effects of bags used for pollinator exclusion on nectar quantity, quality and bee foraging in a field environment. Contrasting temperature treatments (28 °C, 21 °C, 28/16 °C) reveal environment effects or G × E interactions for nectar volume (µl / floret), concentration (°Brix), and sugar composition (% sucrose). Bags used to exclude sunflower pollinators resulted in nectar volumes greater than plants with unrestricted access for bees (= open-pollination), and in ˜5-fold increased visitation by wild bees after bags were removed. Differences in bee visits to plants that were previously bagged versus plants never bagged decreased over the 2 h following bag removal. Though genetic variation in sunflower nectar is affected by the environment and G × E interactions, improving pollination via plant breeding still appears feasible. Future research on intraspecific variation in pollen rewards could be helpful, especially because pollen has received little research compared to nectar. For research with nectar or pollen, it seems desirable to measure floral rewards with methods that don’t rely on pollinator exclusion (bags or cages), which should provide more realistic data on what pollinators experience while foraging.