Abiotic influences on seed germination of three spring flowering Asteraceae annuals from the winter-rainfall region of South Africa

Abstract

For a few weeks of each year large parts of the Western Cape, South Africa burst into a magnificent riot of flowering colours. The timing and longevity of the winter-rainfall season, desiccation sensitivity and poor longevity of seeds are major factors affecting the germination in species with intermediate seeds. Three Asteraceae species; Arctotis hirsuta, a vulnerable, red-listed species, Cotula duckittiae, an endemic species and Oncosiphon suffruticosum, a traditional medicinal species presented germination challenges when introduced into the Kirstenbosch National Botanical Garden annual display beds from wild-collected seed. The study aimed to evaluate temperature, light, and dark influences in breaking seed dormancy of these species. Experiments consisted of constant and alternate temperature (7, 12, 17, 22, 27°C, 12/22°C and 17/27°C) treatments in combination with continuous light, darkness, and equal alternate (12-h cycles) light and darkness using laboratory incubation. Results showed that germination of A. hirsuta responded to temperatures ranges of 22 and 27°C under a continuous light period. C. duckittiae recorded significant germination of ≥60% under a continuous dark period as well as with a temperature variation of 12/22°C under cyclic light and dark conditions. In O. suffruticosum, the highest germination was achieved at 12°C with temperature highly significant. The study presented advanced germination strategies for future restorative purposes of wild populations, botanical displays, and commercial potential of spring flowering species.