The Effect of Temperature, Light and Gibberellic Acid (Ga₃) on the Germination of Australian Everlasting Daisies (Asteraceae, Tribe Inuleae)

Abstract

Australian everlasting daisies have considerable potential as bedding plants, but little is known about their germination requirements. In ten taxa of everlasting daisies (Asteraceae, Tribe Inuleae) examined, germination in petri dishes was optimum over the temperature range 10-20°C with little or no germination at more extreme temperatures (5 and 30°C). Light stimulated germination in seven of the ten tare; Erymophyllum ramosum (A. Gray) Wilson, Craspedia sp., Leucochrysum fitzgibbonii (F. Muell.) Wilson, Waitzia suaveolens var. flava Wilson, Rhodanthe chlorocephala subsp. rosea (Hook.) Wilson, R. chlorocephala subsp. splendida (Hemsley) Wilson and R. floribunda (DC.) Wilson. In the dark, gibberellic acid (GA₃, 50 mg L^-1) stimulated germination to similar levels observed in light-treated seed. Schoenia filifolia subsp. subulifolia and S. cassiniana were not affected by light regime, but in both taxa germination was improved by the addition of GA₃. By contrast, germination in Rhodanthe humboldtiana, which also had no response to light, was inhibited by GA₃. In most species, germination in the dark was similar over the GA₃ concentration range 1-100 mg L^-1, but 500 mg L^-1 was often inhibitory. Germination was optimised under temperature and light conditions related to maximising survival of seedlings which germinate near the soil surface during winter in the arid interior habitat of central Australia.