Pollen quantity, but not grain size, is correlated with floret size in in cultivated sunflower, Helianthus annuus L.

Authors: Prasifka, Jarrad; Portlas, Zoe; Hulke, Brent

Submitted to: Plant Genetic Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2023
Publication Date: 9/25/2023
Citation: Prasifka, J.R., Portlas, Z.M., Hulke, B.S. 2023. Pollen quantity, but not grain size, is correlated with floret size in in cultivated sunflower, Helianthus annuus L.. Plant Genetic Resources. 2023. https://doi.org/10.1017/S1479262123000709.
DOI: https://doi.org/10.1017/S1479262123000709

Interpretive Summary: The amount of pollen produced by sunflowers is important to sunflower breeders and also bees that use this pollen for food. It also appears that pollination with larger-sized pollen grains is more likely to produce seed. Publicly-developed sunflower lines were evaluated in 2016 and 2017 for the amount of pollen and size of pollen grains contained in individual flowers called florets. Lines showed differences in pollen quantity and pollen grain size over two years. More pollen was found in lines with larger florets. However, pollen grain size was not related to pollen quantity or floret size. It did not appear that sunflower breeding has produced more or larger pollen over time. Because some sunflower lines contain normal amounts of pollen inside florets but appear to release less pollen during bloom, there may be important differences in how pollen is pushed out of florets and exposed to pollinating insects.

Technical Abstract: Cultivated sunflower (Helianthus annuus L.) pollen helps attract wild and managed bees needed to produce hybrid seed. Pollen quantity and grain size (˜ quality) are affected by the environment, but are also heritable traits of interest for breeding. Samples of florets from public inbred B-lines (maintainer) and R-lines (restorer) lines were used to evaluate pollen quantity and quality, test for trait correlations, and determine if line development has changed pollen traits. Pollen quantity (˜ 25,000–67,000 grains per floret) and diameter (˜ 30–37 µm) were similar to previous reports and correlated between 2016 and 2017. Pollen quantity per floret was positively correlated with floret size (area; mm2) but floret sizes and pollen quantity were unrelated to pollen grain size. Groups of lines released relatively early (1968–1986) or late (1988–2006) did not differ in pollen quantity or size, and male (R-line) parents did not produce larger grains. The strong, positive correlation between floret size and pollen quantity reveals a possible trade-off because wild bees generally prefer sunflowers with shallower florets. The apparent lack of change in pollen quantity or pollen grain size over time (and lack of increased pollen size in R-lines relative to B-lines) suggests that the quantity and quality of pollen may not be limiting factors in the success of inbred lines or resulting hybrids. Though sunflower lines with larger florets contain more pollen, additional variation in pollen visible on sunflower heads may relate to the timing or completeness of pollen extrusion from anther tubes.