SEED STRATIFICATION AND GERMINATION STRATEGY IN THE MEDITERRANEAN PINES PINUS-BRUTIA AND PINUS-HALEPENSIS

The ecophysiology of germination in Pinus brutia and P. halepensis was studied in seeds collected from different areas of Greece. In regard to the temperature range of germination, both P. halepensis and the so uthern provenance (Lasithi, Crete) of the East Mediterranean pine, P. brutia, follow a typical Mediterranean pattern. In the latter species, dramatic differences in the degree of dormancy were noted among the t hree provenances investigated; in all seed lots however, 20 degrees C was clearly the optimal temperature for germination. Stratification re sulted in a considerable promotion of P. brutia seed germination. Neve rtheless, the inductive effect of stratification was shown to differ a mong the three provenances used, escalating from a simple increase of germination rate (in the southern seed lot from Lasithi, Crete) throug h a broadening of the temperature range of germination (in the interme diate lot from Thasos Island) to, finally, a dramatic release from a p articularly deep dormancy (in the northern lot from Soufli). These dee ply dormant seeds of the latter provenance displayed an absolute strat ification requirement; prolonged illumination or seed coat scarificati on could not substitute for the promotive effect of prechilling. A con siderable interaction between far-red light and stratification was rev ealed in the dormant seeds of P. brutia (Soufli provenance); far-red p ulses during stratification could either cancel or diminish the germin ation promotion induced by low temperatures. The differences observed in the germination behaviour among the various P. brutia provenances m ay be attributed to a variable ecophysiological strategy in regard to the temporal pattern of seedling emergence and establishment. Accordin g to the variants of this strategy, seed germination is timed to occur during either spring (in regions with relatively cold and moist clima tes), or autumn and early winter (in southern, mild and dry areas) or both (in intermediate conditions).