Germination and morpho-phenological traits of Allium melananthum, a rare species from south-eastern Spain

The germination and life cycle of the rare species Allium melananthum, endemic to southeast Spain, were investigated. One alternating and four constant temperature regimes and two light conditions were tested. Gibberellic acid and cold or warm stratification were used as dormancy breaking treatments. The results showed that light can inhibit seed germination, although the light inhibitory effects varied with temperature. In continuous darkness, seed germination was hardly affected by temperature, but in alternating light/darkness it was sensitive to extreme temperatures of 25 and 10 °C, while mild temperatures of 15-20 °C permitted successful germination. However, a dormant stage was observed in a small fraction of seeds, which was only overcome by warm stratification. By contrast, cold stratification induced strong secondary dormancy. This germination pattern shows that primary and secondary dormancy, temperature and light play pivotal roles as components of the germination-timing strategies of A. melananthum. As regards its life cycle, the juvenile phase in a low proportion of individuals (0.93%) lasted 2 years from seeding, while 56.7% of individuals were capable of producing bulblets in the third year. We suggest that at least two growing seasons post seeding are necessary in the nursery to obtain suitable material for the introduction or reinforcement of A. melananthum populations in their natural habitat.