Wild bee visitation unaffected by disparate nectar phenotypes in a sunflower inbred line population

Variation in the quality, quantity, or accessibility of nectar and pollen within plant species is a potential target for plant breeding, both to enhance pollination and to support nutritional needs of pollinators. A biparental population of sunflower (Helianthus annuus L.) inbred lines that varied for nectar quantity and quality was used to determine whether nectar phenotypes influenced wild pollinator preference under field conditions in a primary North American sunflower production area. Under field conditions, nectar quality (% sucrose) was generally lower than in a controlled environment, and % sucrose was inversely related to nectar volume. As a result, inbred lines generally fell into groups with disparate nectar phenotypes that were either high sucrose and low volume or low sucrose and high volume. Nectar accessibility, as measured by floret size, did not differ between the groups. Though pollinator visits to sunflower inbred lines varied approximately threefold and were correlated between years, analyses of covariance on pollinator observations did not show a significant effect of the two common nectar phenotypes in either of 2 years. Several non-mutually exclusive explanations for the lack of effect of nectar phenotype are plausible. Ongoing efforts to enhance sunflower pollination would benefit from additional work with the plant (resolving trait correlations and potential trade-offs), pollinators (discovery of latent factors that may influence bee preference), and the effects of the environment on plant–pollinator interactions.