Improved germination of silverleaf phacelia (Phacelia hastata Douglas ex Lehm. var. hastata)

Abstract

Silverleaf phacelia (Phacelia hastata Douglas ex Lehm. var. hastata [Hydrophyllaceae]) is a versatile and hardy native plant species with an aesthetically pleasing flower, silver-tinged leaves, and the ability to respond positively to nursery propagation protocols. Attempts to germinate this species without suitable pretreatment, however, have resulted in low and erratic germination due to seed dormancy, even though previous anecdotal studies have identified seed treatments for freshly harvested seeds. After-ripened seeds were subjected to seed structure identification and the following experiments to classify dormancy and to determine effective and efficient seed treatments for growers: 1) examination of water uptake; 2) growth of excised embryos; 3) effect of gibberellic acid; and 4) effect of mechanical scarification. Based on the results of all observations and experiments, dormancy was classified as physiological. Germination was most successful with excised embryos (100%), scarification (87%), and GA soak (48%), with scarification being the most effective and labor-efficient method for growers to use. Note that the highest treatment of GA, 1000 mg/l (1000 ppm), was not high enough to determine peak and toxicity levels, indicating that phacelia may respond to higher levels of GA.