Germination ecology of two endemic multipurpose species of Erythrina from Ethiopia

Forest Ecology and Management

ELSEVIER

Forest Ecologyand Management 65 (1994) 81-87

Germination ecology of two endemic multipurpose species of Erythrina from Ethiopia Demel Teketay l Swedish UniversityofAgriculturalSciences, Facultyof Forestry, Departmentof Forest VegetationEcology, S-901 83 Umed, Sweden (Accepted 2 November 1993)

Abstract Erythrina brucei and Erythrina burana are multipurpose trees which are endemic to Ethiopia. Both species, besides serving many purposes, have an important advantage in that they can be easily propagated vegetatively. However, little is known about their propagation by seed. Several experiments were conducted to investigate the effects of light, temperature and scarification on the germination of the seeds. The seeds of both species exhibited dormancy, although to different degrees, caused by impermeable hard seed coats. In E. brucei, the highest germination percentage (90%) was obtained from seeds placed under direct light from fluorescent tubes coupled with fluctuating day (20 °C ) and night ( 10-12 °C ) temperatures as well as from seeds treated with boiling water for 5 s. Similarly, in E. burana, the highest germination percentage (85%) was obtained in seeds placed at a constant temperature of 25°C in a thermogradient as well as in seeds treated with concentrated sulphuric acid for 1 h . Therefore, for a higher rate and percentage of germination, it is recommended that the seeds of E. brucei be immersed in boiling water for 5 s. However, since the dormancy of seeds of E. brucei is relatively low, untreated seeds may also be used to obtain a reasonable cumulative germination percentage (about 80%). In the case ofE. burana, although a higher percentage and rate of germination can be obtained using sulphuric acid, it is recommended that untreated seeds should be used at a higher sowing density to compensate for the dormancy until a cheap, safe, convenient and rapid method of germination is found. The further investigation of growth characteristics, reproductive biology/ecology as well as performance in agroforestry of both species is recommended. Keywords:Erythrina spp.; Germination; Multipurpose tree; Endemic tree 1. Introduction Erythrina brucei Schweinf. and Erythrina burana Chiov. are leguminous trees which are found growing naturally only in Ethiopia (Thulin, 1989 ). A description of both species, their habitat/ecology and distribution within Ethiopia is ~Permanent address: Alemaya University of Agriculture, Faculty of Forestry, P.O. Box 138, Dire Dawa, Ethiopia.

given by Thulin (1989). The seeds of E. brucei are about 12-20 m m long, about 8-10 m m wide and there are about 1600 seeds per kilogram, while those o f E . burana are about 7-11 m m long, 5-10 m m wide and there are about 3200 seeds per kilogram. Seeds of both species are red to brownish red in colour. The importance of E. burana is discussed elsewhere (Demel Teketay, 1990; Demel Teketay and Assefa Tegineh, 1991 a). This species is one of the components of

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D. Teketay / Forest Ecology and Management 65 (1994) 81-8 7

a traditional tree crop based agroforestry practice in coffee producing areas of Harerge, eastern Ethiopia (Demel Teketay and Assefa Tegineh, 1991b). Erythrina brucei is also used for different purposes, providing fuelwood, feed, construction material, live posts and hedges. It is one of the species which is used in traditional apiculture to place beehives. Thulin ( 1989 ) noted that the wood is very soft and hollowed out branches are used for traditional beehives. Erythrina brucei also fixes atmospheric nitrogen, thereby improving the fertility of the soil. Both species have an important advantage in that they are easily propagated vegetatively; specimens attained (personal observation) a height of about 50-60 cm within 6 months after sowing, indicating that they are fast growing species and thus have potential for both agroforestry practices and rehabilitation programmes. However, despite the fact that these species are multipurpose, very little is known about their propagation by seed. This may be attributed to their easy propagation by cuttings. Seeds of both species exhibit dormancy. The objective of this work, therefore, was to investigate the germination requirements of these species and thus provide background information for future research.

2.2. Experiments

The experiments were undertaken both in Sweden and Ethiopia. A total of 22 treatments of E. brucei (Table 1 ) and 28 treatments of E. burana (Table 2) were carried out involving light, temperature and scarification. In Sweden, three experiments involving light, temperature and scarification were carried out. In the light experiment, 300 seeds of both species were subjected to three different treatments: direct light from fluorescent tubes, light filtered through green leaves and darkness in four replicates. All were placed in a Jacobson germination apparatus set at 20°C during the day and 10-12°C at night. In the temperature experiment, to find out the optimum temperature for germination, seeds were placed in a thermogradient apparatus at 10, 15, 20, 25 and 30°C. Here, 100 seeds were used from each species. Every treatment had 20 seeds each in two replicates. In the scarification experiment, concentrated sulphuric acid and hot water treatments were used with the objective of improving the rate and percentage germination of Table 1 List of treatments in Erythrinabrucei (Treatments 1-16 were carried out in Sweden and Treatments 17-22 were carried out in Ethiopia) No. Treatment

2. Materials and methods

2.1. Seed collection

Seeds of E. brucei were collected from Addis Ababa (9 ° 12'N, 38°43'E) and those of E. burana from Harerge, within a 30 km radius of Harer town (9 ° 20' N, 42 ° 10' E), in March and April 1991 and 1992. Some of the seeds were taken to the Swedish University of Agricultural Sciences (SUAS), Department of Forest Vegetation Ecology, where some of the experiments were undertaken between May and August 1991. The seeds collected in 1992 were used in other experiments which were conducted at Alemaya University of Agriculture (AUA), Faculty of Forestry Nursery (Ethiopia) between May and July 1992.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Light direct from fluorescent tubes Light filtered through green leaves Darkness Temperature, 10°C Temperature, 15°C Temperature, 20°C Temperature, 25°C Temperature, 30°C Control for treatments 10-16 Concentrated sulphuric acid for 5 min Concentrated sulphuric acid for 10 min Concentrated sulphuric acid for 15 min Concentrated sulphuric acid for 20 min Hot water for 30 s and removed immediately Hot water for 30 s and left until water reached room temperature Hot water for 60 s and removed immediately Hot water for 5 s and removed immediately Hot water for 15 s and removed immediately Hot water for 30 s and removed immediately Hot water for 60 s and removed immediately Manual scarification Control for treatments 17-21

D. Teketay / Forest Ecology and Management 65 (I 994) 81-87 Table 2 List of treatments in Erythrina burana (Treatments 1-18 were carried out in Sweden and Treatments 19-28 were carried out in Ethiopia) No. Treatment 1 2 3 4 5 6 7 8 9 l0 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Light direct from fluorescent tubes Light filtered through green leaves Darkness Temperature, 10°C Temperature, 15°C Temperature, 20°C Temperature, 25°C Temperature, 30°C Control for treatments 10-18 Concentrated sulphuric acid for 5 min Concentrated sulphuric acid for 10 min Concentrated sulphuric acid for 15 min Concentrated sulphuric acid for 20 rain Hot water for 30 s and removed immediately Hot water for 1 min and removed immediately Hot water for 5 min and removed immediately Hot water for 10 min and removed immediately Hot water for 15 min and removed immediately Hot water for 5 s and removed immediately Hot water for 15 s and removed immediately Hot water for 30 s and removed immediately Hot water for 60 s and removed immediately Concentrated sulphuric acid for 30 min Concentrated sulphuric acid for 40 min Concentrated sulphuric acid for 50 min Concentrated sulphuric acid for 60 min Manual scarification Controlfor treatments 19-27

the species. Seeds from both species were treated with sulphuric acid for 5, 10, 15 and 20 min before they were allowed to germinate. In each of these treatments, 100 seeds were used from each species in four replicates. A further 100 seeds of each species were not treated (control). In the hot water treatment, seeds ofE. burana were immersed in boiling water (100°C) for 30 s, 1, 5, 10 and 15 min and then removed immediately. Seeds ofE. brucei were immersed in boiling water for 30 s, removed immediately, immersed for 30 s and soaked until the water reached room temperature (21 ° C ), immersed for a further 60 s and then removed immediately. For both species, each treatment had 50 seeds in five replicates. Fifty seeds from each species were used as a control. In all the treatments, seeds were enclosed in

83

transparent plastic boxes (6 cm X 3 cm X 1.5 cm) on cotton which was kept moist with distilled water. In Ethiopia, 600 seeds of E. brucei and 1000 seeds of E. burana were used in experiments involving scarification aimed at improving the rate of germination and percentage germination obtained from experiments undertaken in Sweden. Seeds of both species which were treated with hot water in Sweden died. Therefore, the experiment was repeated by immersing seeds of both species in boiling water for 5, 15, 30 and 60 s. Acid scarification was also repeated for seeds ofE. burana to improve germination. This time, the seeds were treated with concentrated sulphuric acid for 30, 40, 50 and 60 min. One hundred seeds from each species were scarified manually by piercing a small hole at the hilum using a needle. In the control, 100 seeds from each species were used. In each treatment, 100 seeds were used in five replicates of 20 seeds. The seeds in all the treatments were enclosed in transparent plastic boxes ( 10.5 cm X 10 cm X 2 cm) on cotton which was kept moist until the end of the experiments. The boxes were then placed on a bench in a lath-house which received direct sunlight.

2.3. Assessment The seeds were considered as germinated when the radicle reached about the size of the seed in all the experiments. Germinated seeds were counted and discarded.

2.4. Statistical analysis The data from all the experiments were arcsine transformed (Zar, 1984) and analysed using STATGRAPHICS (STSC, 1986) and the significance of treatment means were tested by one-way ANOVA. The Tukey test was used to compare differences between individual treatment means in each experiment. 3. Results

Treatment means from the light experiments in both species were not significantly different,

D. Teketay / Forest Ecology and Management 65 (1994) 81-87

84

suggesting that light is not a limiting factor for the germination of the seeds. In E. brucei, the highest germination percentage (90%) was obtained from seeds which were placed in fluctuating day (20 oC ) and night ( 10-12 ° C) temperatures and exposed to direct light from fluorescent tubes. However, in E. burana, the highest germination percentage (85%) was obtained in seeds placed at a constant temperature of 25 °C in the thermogradient and those treated with sulphuric acid for 1 h. Germination ofE. brucei was faster in seeds treated with hot water for 5 s (Fig. 1 ), while in E. burana, much faster germination was obtained from seeds treated with the acid (Fig. 2). In the case of temperature experiments (Figs. 3 (B) and 4 (B) ), treatment means were not significantly different in E. brucei, while they differed significantly in E. burana (F (4, 5 ) = 5.483, P<0.0451 ). The highest germination percentage (80%) for E. brucei was obtained from seeds that were placed at 30°C while that ofE. burana (85%) was obtained from seeds placed at 25 oC. Treatment means from the scarification experiments (Figs. 3(C), 3(D), 4(C) and 4 ( D ) ) carried out in Sweden and Ethiopia had highly significant differences in E. brucei (scarification treatments in Sweden, F (7, 24)=56.582,

P < 0.0000; scarification treatments in Ethiopia, F (5, 24)=91.448, P<0.0000) and E. burana (scarification treatments in Sweden, F (9, 30)=81.165, P<0.0000; scarification treatments in Ethiopia, F (9, 40)=20.207, P < 0.0000). In E. brucei, the mean germination percentage at 10 ° C was significantly different from that obtained at the other temperatures (Fig. 3 (B) ). In the second scarification experiment (Fig. 3 (D) ), the mean germination percentage obtained in Treatments 19 and 20 were significantly different from those obtained in the other treatments, while Treatment 18 gave significantly different results from Treatments 17, 21 and 22, which in turn did not differ significantly from each other. In E. burana, Treatment 7 gave significantly different results from all the other treatments in the temperature experiment (Fig. 4 (B)), while the results of Treatments 4 and 5 differed significantly from those of Treatments 6 and 8. In the second scarification experiment (Fig. 4 (D)), the mean germination percentages obtained in Treatments 23, 24, 25 and 26 were not significantly different from each other; however, they differed significantly from those obtained in the other treatments. In contrast, the germination percentages obtained in Treatments 27 and 28

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did not differ significantly from each other but were significantly different from those of Treatments 21 and 22, which in turn were significantly different from each other and those of Treatments 19 and 20. The germination percentages of the controls in E. brucei were 80% and 81% from scarification experiments carried out in Sweden and Ethiopia,

respectively, indicating that the dormancy of the seeds is relatively low. The corresponding values in E. burana were 44% and 53%, suggesting that the seeds of this species possess a higher degree of dormancy than E. brucei. In general, germination was faster in E. brucei than in E. burana. The results from the scarification experiments revealed that dormancy of seeds in E. burana is

D. Teketay /Forest Ecology and Management 65 (I 994) 8 I-8 7

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imposed by hard seed coats which are impermeable to water.

4. Discussion

The seeds of both species were insensitive to light. The relatively higher germination percentages (Figs. 3(A) and 4(A)) obtained from seeds in the light treatments may be attributed to the fluctuating day and night temperatures which might have helped to break the dormancy of the seeds (Bewley and Black, 1982, 1985; Mayer and Poljakoff-Mayber, 1982; Beardsell and Richards, 1987). Germination ofE. burana seeds was inhibited at 10°C, while it was only 5% at 15°C, increasing as the temperature increased to 25 °C and declining thereafter, suggesting that the optimum temperature for germination of this species is 25°C. Erythrina burana grows mostly at lower altitudes, especially in valleys, where the average annual temperature is warm during most months of the year. In E. brucei, the highest germination percentage (80%) in the temperature experiment was

obtained at 30°C (Fig. 3(B)). Moreover, germination ofE. brucei was faster at 30°C than at the other temperatures. Five and eight seeds rotted from boxes placed at 20 ° C and 25 ° C, respectively. The species was expected to have a lower optimum germination temperature (20-25 ° C) than E. burana as it grows at higher altitudes, where the temperature is generally mild. The rotting of seeds may be accounted for by this variation. Seeds of E. brucei exposed to hot water died, except those which had been treated only for 5 and 15 s. Similarly, seeds of E. burana exposed to hot water for more than 1 min died. This suggests that the seeds of both species are very sensitive to high temperatures. In the acid scarification, germination in seeds of E. brucei increased with increased time of exposure to the acid up to 10 min but declined with further in. creases in exposure time. Manual scarification improved germination in E. brucei (Fig. 1 ) while it reduced germination in E. burana (Fig. 2 ). From a similar work carried out in Tanzania, Laurent and Chamshama (1987) reported that a pre-sowing treatment of seeds with either hot water or concentgated sulphuric acid increased

D. Teketay / Forest Ecology and Management 65 (1994) 81-87

the rate of germination and percentage germination of Erythrina abyssinica Lam. ex DC. (8084%), while none germinated from the untreated seeds. 5. Conclusion Because of their fast growth and multiple uses, E. brucei and E. burana seem potential candidates for agroforestry, rehabilitation and conservation programmes. However, the seeds of both species exhibit dormancy, although to varying degrees. Therefore, for a higher rate and percentage of germination, it is recommended that the seeds of E. brucei be treated with hot water (100 °C) for 5 s. However, since the dormancy of the seeds is relatively low, untreated seeds may be used to obtain a reasonable cumulative germination percentage (around 80%). In the case of E. burana, the treatment of seeds with hot water did not improve, but rather reduced germination. Therefore, although a high rate and percentage of germination can be obtained by treating the seeds with sulphuric acid for 1 h, the use of higher sowing density of untreated seeds is recommended to compensate for dormancy in large-scale seedling production. Using concentrated sulphuric acid is dangerous, expensive and inconvenient for the large-scale production of seedlings. Moreover, it may not be available on the market in developing countries like Ethiopia. Further investigation is required to find a cheap, convenient and rapid method of germinating E. burana seeds. In addition, investigation of the growth characteristics, reproductive biology/ ecology as well as the performance in agroforestry practices of both species is recommended.

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Acknowledgements I am grateful to the following institutions and persons for their help during the research: Faculty of Forestry (AUA), Departments of Forest Vegetation Ecology and Silviculture (SUAS), Rune Johansson, Ato Tamerat Abebe and Ato Abdurazak Abdulahi. References Beardsell, D. and Richards, D., 1987. Ecological aspects of seed germination. In: P.J. Langkamp (Editor), Germination of Australian Native Plant Seed. The Australian Mineral Industries Research Association, Melbourne/ Sydney, pp. 14-19. Bewley, J.D. and Black, M., 1982. Physiology and Biochemistry of Seeds in Relation to Germination. Springer, Berlin/Heidelberg, 375 pp. Bewley, J.D. and Black, M., 1985. Seeds, Physiology of Development and Germination. Plenum Press, New York, 367 pp. Demel Teketay, 1990. Erythrina burana, promising multipurpose tree from Ethiopia. Agrofor. Today, 2 (4): 13. Demel Teketay and Assefa Tegineh, 1991a. Shade trees of coffee in Harerge, eastern Ethiopia. Int. Tree Crops J., 7: 17-27. Demel Teketay and Assefa Tegineh, 199 lb. Traditional tree crop based agroforestry in coffee producing areas of Harerge, eastern Ethiopia. Agrofor. Syst., 16: 257-267. Laurent, N. and Chamshama, S.A.O., 1987. Studies on the germination of Erythrina abyssinica and Juniperus procera. Int. Tree Crops J., 4: 291-298. Mayer, A.M. and Poljakoff-Mayber, A., 1982. The Germination of Seeds. Pergamon Press, London, 270 pp. STSC, 1986. STATGRAPHICS. Statistical Graphics Corporation, EXEC U STAT, and Lauer Software, New York. Thulin, M., 1989. Fabaceae. In: I. Hedberg and S. Edwards (Editors), Flora of Ethiopia, Vol. 3. The National Herbarium, Addis Ababa, pp. 49-251. Zar, J.H., 1984. Biostatistical Analysis, 2nd edn. PrenticeHall, Englewood Cliffs, N J, 718 pp.