Aims: Albizia julibrissin is one of the ecologically valuable tree species in the Hyrcanian forest at the Norht of Iran that is endangered due to Fusarium wilt disease. Seeds of these trees have low germination because of their hard coat and dormancy. One of the most effective methods to improve the germination characteristics is seed irradiation during pre-sowing processes. Present study was conducted to improve seed germination characteristics.
 Materials & Methods:  Experiment was arranged by completely randomized design in four replications, five treatments and one control. Seeds were radiated with 60 cobalt source emitting gamma rays at the rate of 0.013 Gray/sec and different doses of gamma rays: 15, 25, 50, 100 and 150 Gray (Gy). All of the seeds were sowing in the moist stratification at 25°C.
Findings: Seed germination started simultaneously 28 days after sowing. Results showed that there is significant difference in germination characteristics between treated seeds and control (p˂0.05). The highest value of seed germination was observed in the 15 Gy (86%), the highest seed vigor index was in 15 Gy treated seeds (266.6), the highest germination speed index  were in 15 and 150 Gy (12.17 and 12.32 seed number day^-1 respectively) and the highest mean daily germination were in 15, 50, 100 Gy (7.46, 7.32 and 7.34 number/day respectively).
 Conclusion: Increasing seed germination characteristics was observed in seeds that radiated by low dose of gamma radiation. Hence, lower dose (15 Gy) of irradiation treatment can be used to improve the Albizia julibrissin seed germination characteristics.
 

Keywords: Gamma irradiation, Mean Daily Germination, Seed Vigor Index, Seed, Forest, Seed germination

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* Corresponding Author Address: Iran