Temperature-dependent seed germination in Watsonia species related to geographic distribution

The abundance of flowering plants in South Africa provides opportunities for ongoing development of new horticultural subjects. However, a thorough knowledge of their propagation requirements is needed so that successful commercialization can occur. Such understanding includes seed germination, water, nutrient and temperature requirements for growth, resistance to pests and diseases, and the ability to manipulate flowering. In this study, we investigated the temperature and light requirements for germination of four winter-rainfall Watsonia (Iridaceae) species (W. aletroides, W. laccata, W. tabularis and W. vanderspuyiae), two summer-rainfall species (W. gladioloides and W. lepida), and the widely distributed W. pillansii. Germination response to temperature exhibited clear trends that depended on the geographic region from which the plants originated. Species from the winter-rainfall region germinated optimally at 10, 15 and 20 °C, those from the summer-rainfall region germinated best at 15, 20 and 25 °C, and the widely distributed W. pillansii germinated over the entire range from 10 to 30 °C. Continuous light and continuous darkness only influenced germination in W. vanderspuyiae, where it was marginally reduced.