Seed viability and optimal germination conditions of Cedrus atlantica (Manetti ex Endl.) Carrière

Our work is part of the ex situ conservation of the Atlas cedar (Cedrus atlantica (Manetti ex Endl.) Carrière), a threatened and endemic Pinaceae of the Maghreb. Our objectives are to evaluate the viability of seeds from three Algerian cedar groves ecotypes (Thienet El Had, Chelia, Chrea) by the 2,3,5 triphenyltetrazolium chloride (TZ) test and to elucidate the effect of continuous temperatures (15°C, 20°C, 25°C) on their germinative capacity. Moreover, the effects of some physicochemical pretreatments in breaking dormancy and improving germinability were estimated on the seeds of the cedar grove of Thienet El Had. In addition, in the same ecotype, the water stress, as simulated by using the PEG₆₀₀₀ (0 to −2.20 bar), was induced upon seed germination. Results of the TZ test showed variability in seeds’ viability among the three ecotypes with rates of 60, 85 and 90% in those of Chelia, Chrea and Thienet El Had, respectively. However, germination tests revealed the existence of partial dormancy in all tested seeds. Dramatic differences in the degree of dormancy were noted among the three provenances investigated. Untreated seeds of the three ecotypes exhibited maximum germination at 20°C: Thienet El Had (52%), Chelia (32%) and Chrea (7%). The final germination percentage was as high as 76% in seeds soaked in hot water (80°C) for 5 min followed by 56% in seeds treated with GA₃ (150 ppm). The increase in water stress regularly decreases germination with a tolerance threshold corresponding to −2.2 bar.