Effect of scarification, gibberellic acid and temperature on seed germination of two multipurpose Albizia species from Ethiopia

Seeds of Albizia grandibracteata and Albizia gummifera possess seedcoat-imposed dormancy hampering complete, rapid and uniform germination. To overcome this dormancy, seeds of both species were pre-treated with mechanical scarification or concentrated sulphuric acid for 10, 20, 30, 40 and 60 minutes or hot water at 60, 70, 80, 90 and ca.100 degreesC. Besides, scarified seeds of A. grandibracteata were treated with three concentrations of gibberellic acid: 10(-3), 10(-4) and 10(-5) M. To determine the effects of temperature on seed germination, pre-treated seeds from each species were germinated at 15, 20, 25, 30 and 35 degreesC. All scarification treatments improved the germination capacity and Vigour of A. gummifera seeds, the highest being after mechanical scarification followed by sulphuric acid and 80 degreesC hot water treatments. Only mechanical scarification gave the highest germination in R grandibracteata seeds. GA treatment of mechanically scarified seeds resulted in more than 50% germination, and GA(3), 10(-4)M was better than the others were. Germination capacity and the speed of germination were higher at 20 and 25 degreesC in both species; but A. gummifera seeds germinated well over a wider range of temperatures.