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Comparison Of Germination Techniques for Wild Helianthus Seeds¹

Seed dormancy has hampered previous efforts to study Helianthus sp. and to use them in breeding programs for improving the cultivated sunflower, H. annuus L. Several seed treatments were tested to determine their effectiveness in overcoming the strong seed dormancy found in many wild Helianthus sp. The first treatment (referred to as the complete treatment) involved mechanical scarification of the seed, a 1 h soak in a 100 mg/L solution of gibberellic acid (GA₃), plus hull removal. Other treatments were simplifications of this procedure, and three whole seed treatments using GA₃ or ethylene. The results indiicate that treatments which removed the hull and seed coat were the most effective, giving germination of over 90% for many species including the hard-to-germinate annual desert species. Soaking scarified seeds for 1 h in a 100 mg/L GA9 solution increased germination for some accessions. Soaking whole seeds in 100 mg/L GA₃ for 1 h or 50 mg/L 2-chloroethylphosphonie acid for 16 h did not increase germination. Incubating whole seeds for 10 days in either 100 or 1000 mg/L GA₃ increased germination but produced abnormal plants. The complete treatment is recommended despite its complexity because it gives a high germination percentage and varies least from accession to accession.

Key Words: Dormancy • Ethylene • Gibberellic acid • Sunflower • Xerophytes

² Former postgraduate research agronomist, Univ. of California, Davis, and research geneticist, USDA-ARS, Davis, CA 95616; presently research geneticists, USDA-ARS, Davis, CA and Fargo, ND 58105.

Received for publication July 5, 1984.