Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/1997
Publication Date: N/A
Interpretive Summary: Wild sunflowers have developed mechanisms which enable them to survive many different environmental conditions. This survival mechanism also ensures that these plants do not germinate and grow when conditions are unfavorable. However, built in dormancy becomes an impediment when utilizing the wild species for other purposes. Recently, there has been an interest in using wild sunflowers as low maintenance ornamentals, for vegetation of disturbed lands and grasslands, in the cut flower industry, and for crop improvement. In order to do this, the innate dormancy must be broken. We developed a simple quick substrate treatment of the seeds of wild sunflowers with a growth regulator, gibberellic acid which proved to be very effective in increasing germination, sometimes doubling and even tripling germination of nontreated seeds. This substrate was effective on seeds stored for various times and temperatures. It was also discovered that immature seeds of some species of the wild sunflowers had higher germination than more mature seeds. Storage of mature, dormant seeds at various temperatures and times was not able to overcome the dormancy. It appears that harvesting seeds before maturity prevents the accumulation of inhibitors in the seeds. The development of this simple chemical substrate treatment will be particularly useful for obtaining an adequate number of wild species sunflower plants for agricultural improvement of the cultivated sunflower crop.
Technical Abstract: Dormancy in achenes of wild Helianthus species insures 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 the many wild species for domestic purposes. There has been an increasing interest in the use of native species of Helianthus for low maintenance ornamentals, revegetation, as cut flowers, and as a source of genes for the improvement of the cultivated sunflower. The objectives of the study were to evaluate chemical substrates for overcoming dormancy and enhancing germination of two annual species, H. annuus L. and H. petiolaris Nutt., and evaluate the influence of achene maturity, storage time and temperature on germination. A 1 mM gibberellic acid substrate was the most effective chemical treatment for enhancing germination of freshly harvested achenes of H. annuus. Germination of treated achenes was 81%, compared to 38% for the control. With H. petiolaris the rate was 60%, compared to 6% for the control. This substrate enhanced germination regardless of the achene maturity, storage time or temperature. The age of the achenes when harvested influenced germination. Achenes harvested 10 days after flowering generally had higher germination than those harvested 30 days after flowering, especially for H. petiolaris. Storage time and temperature could not overcome the dormancy imposed prior to germination in either species. Utilization of a chemical substrate to enhance germination of wild Helianthus species will allow their use for revegetation, as ornamentals, as cut flowers, and as a genetic resource for cultivated sunflower.