Seed and floret size parameters of sunflower are determined by partially overlapping sets of quantitative trait loci with epistatic interactions


Key message

Floret and seed traits are moderately correlated phenotypically in modern sunflower cultivars, but the underlying genetics are mostly independent. Seed traits in particular are governed in part by epistatic effects among quantitative trait loci.


Seed size is an important quality component in marketing commercial sunflower (Helianthus annuus L.), particularly for the in-shell confectionery market, where long and broad seed types are preferred as a directly consumed snack food globally. Floret size is also important because corolla tube length was previously shown to be inversely correlated with pollinator visitation, impacting bee foraging potential and pollinator services to the plant. Commercial sunflower production benefits from pollinator visits, despite being self-compatible, and bees are required in hybrid seed production, where “female” and “male” inbred lines are crossed at field scale. Issues with pollination of long-seed confectionery sunflower suggest that there may be an unfavorable correlation between seed and floret traits; thus, our objective was to determine the strength of the correlation between seed and floret traits, and confirm any co-localization of seed and floret trait loci using genome-wide association analysis in the SAM diversity panel of sunflower. Our results indicate that phenotypic correlations between seed and floret traits are generally low to moderate, regardless of market class, a component of population substructure. Association mapping results mirror the correlations: while a few loci overlap, many loci for the two traits are not overlapping or even adjacent. The genetics of these traits, while modestly quantitative and influenced by epistatic effects, are not a barrier to simultaneous improvement of seed length and pollinator-friendly floret traits. We conclude that breeding for large seed size, which is required for the confectionery seed market, is possible without producing florets too long for efficient use by pollinators, which promotes bee foraging and associated pollination services.

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The authors acknowledge the assistance of Jonathan Tetlie, Brady Koehler, and Michael Grove in the maintenance and collection of field samples for this work. The assistance of Brian Smart and Cloe Pogoda to the development of figures is also greatly appreciated. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture.


This work was supported by funds from the USDA-Agricultural Research Service (project number 3060-21000-043-00D).

Author information

JRP and BSH developed the experimental design; JRP, BF, and ZMP conducted and validated the phenotypic experiments; QMG, SR, and BSH developed the statistical design, conducted the association mapping and epistasis work, and wrote the manuscript; and all authors contributed to final review and acceptance of the manuscript.

Correspondence to Brent S. Hulke.

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Reinert, S., Gao, Q., Ferguson, B. et al. Seed and floret size parameters of sunflower are determined by partially overlapping sets of quantitative trait loci with epistatic interactions. Mol Genet Genomics 295, 143–154 (2020) doi:10.1007/s00438-019-01610-7

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  • Sunflower
  • Helianthus annuus L.
  • Seed size
  • Corolla
  • Floret
  • Pollinator
  • Confectionery