The genus Callistemon belongs to the family Myrtaceae and comprises 34 species. They are woody aromatic trees or shrubs that are widely distributed in the wet tropics. According to the scientific literature, research on seed germination of this genus was rarely carried out. The germination requirements of Callistemon citrinus and Callistemon linearis were studied under controlled conditions in the laboratory. Seeds of both species were tested for germination at constant temperatures of 25°C, 30°C, 40°C, and at room temperature (23 ± 2°C) coupled with total darkness. Seeds were sown in Petri dishes (0.8% agar water) for 25 days of incubation. The kinetics of germination was determined according to four closely related parameters viz. final germination percentage (FGP), mean germination time (MGT), coefficient of velocity of germination (CVG) and time to 50% germination (T50). The room temperature of 23 ± 2 °C was found optimally suitable for both species, with 80% FGP and 11.1 days MGT for C. citrinus, and only 21.7% FGP and 12.4 days MGT were recorded for C. linearis. Furthermore, significant decrease in FGP was observed in both species at 25°C, 30°C and 40°C of temperature. The analysis also revealed that day 12-15 after seed sowing is suitable for final counts. Due of its very low FGP, seeds of C. linearis need an additional study to determine their viability.

Breaking physical dormancy in some forest seeds is a challenge for scientists and forest managers to obtain an homogeneous germination for larger seed samples. The role played by the seed coat in seed dormancy of six trees with great interest in agroforestry (Robinia pseudoacacia, Leucaena leucocephala, Erythrostemon gilliesii, Styphnolobium japonicum, Acacia dealbata and Brachychiton populneus) was tested by the effects of the pretreatment and its duration on the performance of seed germination, by considering the final germination percentage (FGP) and the mean germination time (MGT). These parameters are estimated at various times of incubation (5, 10 and 15 days) in Petri dishes and stored in darkness at (25 ± 2°C). The pretreatment consists of an immersion of seeds in concentrated sulphuric acid during 30, 60 and 90 minutes. Sowing without pretreatment (control) revealed no germination induction for B. populneus and A. dealbata, except for R. pseudoacacia, L. leucocephala and S. japonica where the germination does not exceed 12% for all the experience duration. Generally, pretreatments were very useful to improve seed germination. The time of immersion into sulphuric acid significantly affected (P < 0.0001) the FGP and the MGT in all studied species. A duration of 30 minutes of soaking was adequate to give a very high rate of germination for L. leucocephala, E. gilliesii, S. japonica and A. dealbata with respective FGP of 100%, 95%, 100% and 100%. However, an extended duration of pretreatment of 60 minutes was necessary for a maximal germination for R. pseudoacacia and B. populneus with FGP of 85% and 100%, respectively. A prolonged duration of 90 minutes of presowing was very fatal for L. leucocephala, A. dealbata and B. populneus. An excellent germinative strength is characterized by a higher FGP and a reduced MGT.