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Seed Maturity, Storage Time and Temperature, and Media Treatment Effects on Germination of Two Wild Sunflowers

USDA-ARS, Northern Crop Science Laboratory,, P.O. Box 5677, Fargo, ND 58105

^* Corresponding author (seilerg{at}fargo.ars.usda.gov).

Dormancy in achenes (seeds) of wild sunflower (Helianthus) species ensures that they do not germinate in temperate climates until conditions are optimal for seedling survival. However, high achene dormancy results in low germination of achenes, precluding utilization of many wild species for domestic purposes. Interest in the use of native Helianthus species for domestic purposes such as low-maintenance ornamentals, revegetation, cut flowers, and genetic improvement of cultivated sunflower has recently increased. The objectives of this study were to evaluate germination media to overcome dormancy and enhance germination of two annual species, H. annuus L. and H. petiolaris Nutt., and to evaluate the influence of achene maturity and storage time and temperature on germination. A1 mM gibberellic acid (GA³) medium was the most effective stimulant in laboratory tests for enhancing germination of H. annuus. Germination of treated achenes was 81%, compared with 38% for the control. Germination of H, petiolaris achenes was 60% with the 1 mM GA³ medium, compared with 9% for the water control. This GA, medium enhanced germination regardless of achene maturity, storage time, or storage temperature. When averaged over all media, achene maturities, and storage times and temperatures, H. annuus had a germination of 41%, compared with only 21% for H. petiolaris. The age of the achenes at harvest influenced germination. Achenes harvested 20 d after flowering generally had greater germination than those harvested 40 d after flowering, especially for H. petiolaris. Storage time and temperature could not overcome the dormancy imposed prior to germination in either species. Utilization of germination media to enhance germination of wild Helianthus species will facilitate their use for domestic purposes.

Received for publication May 28, 1997.