|TETLIE, JONATHAN - University Of Illinois|
|PRISCHMANN-VOLDSETH, DEIRDRE - North Dakota State University|
Submitted to: Plant Genetic Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2018
Publication Date: 3/15/2018
Citation: Portlas, Z.M., Tetlie, J.R., Prischmann-Voldseth, D., Hulke, B.S., Prasifka, J.R. 2018. Variation in floret size explains differences in wild bee visitation to cultivated sunflowers. Plant Genetic Resources. https://doi.org/10.1017/S1479262118000072.
Interpretive Summary: Pollination by both wild bees and honey bees is needed to produce the seeds that are planted by sunflower growers, as well as the seeds and sunflower products used by consumers. Bees often prefer certain types of sunflowers, and the size of the many flowers (florets) that make up a single sunflower head may be an especially important reason for preference, because bees may not be able to drink the nectar at the bottom of very large florets. When one hundred sunflower types were collected and measured, floret lengths of about 7 to 10 millimeters were seen. When lines with shorter or longer florets were grown together, about half of the differences in wild bee choice of sunflower lines could be explained using only floret size measurements. The results suggest that breeding sunflowers with shorter florets could improve pollination. Important additional steps include finding genetic markers that help determine floret size and understanding whether breeding plants for smaller florets produces any unforeseen trade-offs, like a reduction in oil content.
Technical Abstract: Wild and managed bees are needed to move sunflower (Helianthus annuus L.) pollen, both to create hybrid seed and to encourage high, consistent yields when those hybrids are subsequently grown. Among floral traits that influence bee preference, floret size may be critical, as the depth of the corolla affects the accessibility of nectar. Sampling and observation of inbred maintainer (HA) lines were used to assess variation in floret size, and to measure any effects of floret size on pollinator visitation. Among 100 inbreds sampled, there was significant variation among the lines, with floret lengths of 6.8–9.9 mm. Floret length, measured before anthesis, was closely related to corolla depth during anthesis, and was consistent between two years (environments). Pollinator observations on 30 inbred lines showed floret size explained a majority (52%) of the variation in wild bee preference, with a reduction in floret length of 2 mm more than doubling pollinator activity. Though honey bee, Apis mellifera L., colonies were located ˜ 60 m from the plots, near-zero honey bee activity in the sunflowers precluded an assessment of how strongly this managed pollinator is affected by floret length. Production of inbreds and hybrids with smaller florets could enhance sunflower pollination, but genetic markers for floret size are needed to facilitate selection, and an understanding of potential trade-offs also is needed. Information on variation and heritability of other traits, such as pollen and nectar rewards, could help explain residual variation in wild bee visitation to sunflowers.