Interactions between temperature, light and chemical promoters trigger seed germination of the rare Azorean lettuce, Lactuca watsoniana (Asteraceae)

Lactuca watsoniana is an Azorean endemic plant, listed as a priority species for conservation. Although there is a considerable amount of data regarding germination in the genus Lactuca, little is known about seed germination in L. watsoniana, which is an important gap for defining conservation strategies. Seed viability (tetrazolium test) declined from 100 to 30% after four months storage at room temperature over silica gel. We tested the effects of 1) incubation temperature (three alternating temperature regimes); 2) gibberellic acid concentration (four levels); 3) addition of ethephon; and 4) type of light (three modalities) on seed germination (fresh seeds). There was a significant effect of incubation temperature, gibberellic acid concentration and type of light on percentage germination. There were also significant interaction effects of gibberellic acid with all the other studied factors, and the type of light with temperature regime. The optimal treatment was 0.1 mg l^-1 gibberellic acid, ethephon and a red filter at 15/10°C, resulting in 95% germination. Our study allowed the production of hundreds of seedlings that were reintroduced into the original population.