Graduate Thesis Or Dissertation
 

Germination and dormancy of meadowfoam seed

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  • Meadowfoam (Limnanthes spp.) is a potential oil seed crop being developed for commercial production in the Willamette Valley. The seeds are characterized by poor germination at warm temperatures. It would be desirable to overcome this temperature-related dormancy problem so that better stand establishment could be realized from early fall planting. The objectives of this study were to determine the factors influencing seed germination of meadowfoam, characterize the types of dormancy involved, and develop methods of overcoming dormancy. Experiments were carried out with different-aged seed lots of L. alba 'Mermaid,' L- floccosa Howell and a cross of L. floccosa x L.. alba. Germination requirements were investigated by studying seed responses to temperature, light, oxygen, growth regulators, scarification, and chemical inhibitors. The most favorable germination temperatures were 10, 5-15 and 10-20°C. No germination occurred above 20°C. Prechilling 5 days at 5°C promoted germination at higher temperatures. Potassium and thiourea effectively promoted germination, while kinetin, gibberellic acid and ethephon did not. Daily 8-h exposures to light inhibited germination, particularly at the warmer temperatures. Increasing the length of the daily light periods resulted in corresponding decreases in germination. Removal of portions of the seed coat improved germination, as did germination at higher concentrations of oxygen. The seed coat was not a barrier to water uptake by dormant seeds. Water-soluble extracts from the seeds inhibited germination of non-dormant seeds. A number of treatments imposed on meadowfoam seed overcame dormancy partially or fully, suggesting that there are several mechanisms regulating seed dormancy. Evidence from this study suggests that the seed coat is partially responsible, acting as a barrier to diffusion of oxygen and because it is a source of germination inhibitors. Embryo dormancy is also implicated, in that seeds responded to treatment with potassium nitrate. For routine germination testing of meadowfoam, it is recommended that seeds be planted on a substrate moistened with 1 g L⁻¹ KNO₃ and placed in the dark at 10°C for 14 days. If circumstances warrant, additional germination of dormant seed lots can be obtained by germination on substrate of KNO₃ in an atmosphere of 100% O₂.
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