Germination ecology of twelve indigenous and eight exotic multipurpose leguminous species from Ethiopia.
The germination requirements of seeds of 20 leguminous species were studied in three experiments undertaken at Alemaya University, Ethiopia. In the first experiment, seeds were subjected to mechanical scarification, sulphuric acid and boiling water treatments. In the second experiment, they were treated with dry heat at 60, 80 and 100°C. In the third experiment, seeds were placed at different temperature regimes (10, 15, 20, 25 and 30°C) on a thermogradient. Sulphuric acid treatment improved germination in all the species while mechanical scarification improved germination in 18 out of 20 species. Boiling water treatment improved germination in 15 species but proved to be lethal to five species. Similarly, germination was significantly improved in 11 out of 16 species treated with dry heat. Germination was faster and higher at both 25°C and 30°C and the optimum temperature for germination was between 20°C and 30°C for all species. Mechanical scarification, sulphuric acid and boiling water treatments as well as dry heat were effective to overcome seed coat imposed dormancy in the species studied. It was not possible to recommend a treatment which is equally effective for all the species. However, boiling water is a practical method for achieving rapid, uniform and high germination except in five of the species for which it proved to be lethal (Acacia seyal, Caesalpinia decapetala, Acacia tortilis, C. spinosa and A. senegal). In the latter case, either mechanical scarification or sulfuric acid treatment should be used. Seeds of Millettia ferruginea should be sown when they are fresh to get high germination as they tend to lose their viability during storage. It is demonstrated that once the dormancy in leguminous species with hard seed coats is broken, the seeds germinate in wide ranges of temperature. Other species tested were: (indigenous species) Acacia albida [Faidherbia albida]; A. brevispica; Acacia nilotica subsp. indica;A. oerfota; A. seyal; A. sieberiana; A. schimperiana; Cadia purpurea; Entada abyssinica and Millettia ferruginea; and (exotic species) Albizia lebbeck; Delonix regia; Erythrina lysistemon; Leucaena leucocephala; Parkinsonia aculeata and Prosopis juliflora.