Interchangeable effects of gibberellic acid and temperature on embryo growth, seed germination and epicotyl emergence in Ribes multiflorum ssp. sandalioticum (Grossulariaceae)

Morphophysiological dormancy was investigated in seeds of Ribes multiflorum Kitex Roem et Schult. ssp. sandalioticum Arrigoni, a rare mountain species endemic to Sardinia (Italy). There were no differences in imbibition rates between intact and scarified seeds, suggesting a lack of physical dormancy, while methylene blue solution (0.5%) highlighted a preferential pathway for solution entrance through the raphe. Embryos were small at seed dispersal, with an initial embryo:seed ratio (E:S)of ca. 0.2 (embryo length, ca. 0.5 mm), whereas the critical E:S ratio for germination was three times longer (ca. 0.6). Gibberellic acid (GA3, 250 mgÆl)1) and warm stratification (25 C for 3 months) followed by low temperature (<15 C) enhanced embryo growth rate (maximum of ca. 0.04 mmÆday)1at 10 C) and subsequent seed germination (radicle emergence; ca. 80% at 10 C). Low germination occurred at warmer temperatures, and cold stratification (5 C for 3 months) induced secondary dormancy. After radicle emergence, epicotyl emergence was delayed for ca.2 months for seeds from three different populations. Mean time of epicotyl emergence was affected by GA3. Seeds of this species showed non-deep simple (root) -non-deep simple (epicotyl) morphophysiological dormancy, highlighting a high synchronisation with Mediterranean seasonality in all the investigated populations.