Site data for the three wild populations of
Abstract
Entandrophragma bussei Harms ex Engl. (wooden banana) is an important indigenous multipurpose tree species endemic to Tanzania. The species has a long history of human use but recent increased utilization pressure, deforestation and high mortality rate of seedlings threaten the survival of natural populations in the wilderness. Therefore, to facilitate domestication, two experimental studies were conducted to evaluate variations in seed germination and seedling growth of three wild populations at the Directorate of Tree Seed Production Laboratories in Morogoro, Tanzania. Germination percentage, mean germination rate, final germination rate and germination index varied significantly among the populations. In terms of seedling growth there was a significant difference in number of leaves among the populations at 3 months of age. The number of course roots and seedling shoot fresh weight varied significantly among the studied populations at 10 months of age. Ruaha population had the highest survival (56%) followed by Kigwe (41%) and Tarangire being the last (36%). The two experiments have clearly demonstrated the existence of considerable variation in germination and seedling growth traits in E. bussei. These traits may prove to be important tools for selection of suitable seed sources for domestication and tree improvement programmes.
Keywords
- Height
- root collar diameter
- seed
- germination traits
- seedling traits
- Tanzania
1. Introduction
Although often not pronounced, arid and semi-arid areas are critical areas for biodiversity conservation and as sources of livelihoods to many communities. Of the total area of Tanzania, arid and semi-arid cover more than 74% of total land equivalent to 88.6 million hectares comprising about 74% of plant species found in East Africa [1].
Despite the importance,
To design effective domestication and tree improvement programmes for high value important species with wide distribution range like
2. Materials and methods
2.1 Study area
This study was carried out between February 2020 and January 2021 at the Directorate of Tree Seed Production (DTSP) Laboratories in Morogoro, Tanzania. The DTSP is one of the Directorates of Tanzania Forest Services Agency (TFS) with the mandate to produce, procure and market high quality tree seeds and other propagating materials in Tanzania.
Morogoro region is located at 6.8278° S and 37.6591° E and experience sub-humid climate with average annual temperature of 25°C, annual rainfall of about 935 mm, relative humidity of about 75% and altitude of around 550 m.a.s.l. Seeds of
Population | Administrative Region | Agroecological zone | Location | Elevation (m) | Rainfall (mm) |
---|---|---|---|---|---|
Ruaha | Iringa | Southern Highlands | 7°75’S, 34°98′E | 945 | 1100 |
Kigwe | Dodoma | Semi-arid | 6°08’S, 35°51′E | 1039 | 650 |
Tarangire | Manyara | Arid | 3°87’S, 36°01′E | 1195 | 550 |
2.2 Fruits collection and processing
Fruits were collected from a total of 15 parent plus trees (5 from each site) in the three regions in August 2019 and stored under room temperature at the DTSP until February 2020. The parent trees had heights and diameter at breast heights (DBH) ranging from 15 to 20 m and 54–104 cm, respectively. From each plus tree, 20 ripe fruits without any damage or malformation were collected making 100 fruits per population and 300 fruits for the three populations. The collected fruits were packed and labelled appropriately and transported to DTSP for further processing. Fruits were left to dry under the house shade for 14 days to allow natural opening of the capsules. Seeds were extracted by shaking the capsules using hands and cleaned by hands to remove debris. The extracted seeds were finally stored under shade until time of use for seed germination and seedling growth experiments.
2.3 Germination experiment
Seed germination study was conducted in the germination laboratory at DTSP where temperature ranged from 10–25°C. The experiment was laid out in a randomized arrangement with three populations replicated four times. During the experiment, twelve rectangular germination trays (24 x 18 x 11 cm) that contained sand (that had been washed to remove silt and organic matter) were used for each population. In each tray, 25 cleaned seeds were sown (after the removal of the wings) to a uniform depth of 1 cm making a total of 300 seeds per population and 900 seeds per experiment. The sand was water-irrigated manually twice per day (in the morning and in the evening) to keep the sand continuously moist without becoming waterlogged. Germinated seeds were counted first on the 12th day after seeds were sown and the emergence of a visible protrusion of cotyledons above the substrate surface. During the experiment, the number of dead seeds was also recorded on the 34th day. The seeds count was done for 34 days after which no more germination was observed. At the end of the 34-day observation period, ungerminated seeds were removed and condition of the embryos was physically inspected.
2.4 Seedling growth experiment
Seedling growth experiment was also established in a randomized arrangement with three populations replicated three times to assess the development of
2.5 Data analysis
Germination period (GP) was determined as number of days from first observed germination (FOG) to where no more germination was observed (NMG) i.e. GP = NMG – FOG [15]. Germination percentage (GC) was determined as the ratio of the total germinated seeds (TGS) to the total of the seeds sown (TSS) i.e. GC = (TGS/TSS) x 100. Germination value (GV) was computed as GV = (∑DGs/N) GP/10 where GV = Germination value, GP = Germination percentage at the end of the test, DGs = Daily germination speed, obtained by dividing the cumulative germination percentage by the number of days since sowing, N = the number of daily counts, starting from the date of first germination and 10 = Constant [2, 16]. Mean germination rate (MGR) was calculated as MGR = ∑ F/ ∑ FX where F = Number of germinated seeds on a particular day and X = Number of days taken for seeds to germinate. Final germination (FG) was computed as FG = GS/ Dt where GS = Number of seeds germinated when there is no more germination and Dt = Total number of days taken for particular seeds to germinate. Germination index (GI) was obtained from GI = ∑ Gt/Dt where Gt = is the number of germinated seeds on day t and Dt = is the time corresponding to Gt in days. We examined assumptions of parametric test for germination and growth traits using standard diagnostic plots in package ggplot2 and Shapiro–Wilk’s Test. Growth variables that did not meet the assumptions were log transformed and germination percentage was arcsine transformed to reduce skewness in frequency distribution and to improve homoscedasticity. Comparison in germination and growth traits between populations was done using One-way ANOVA and means were compared by using Tukey’s Honestly Significant Difference (Tukey’s HSD) post hoc test. Pearson Product Moment Correlation (
3. Results
3.1 Seed germination
Germination in the laboratory started within 12 days for all the populations (Figure 2). Gradual increase in seed germination was experienced until day 24 for both Kigwe and Tarangire populations after which germination levelled off (Figure 2). However, Ruaha population had the gradual increase in germination up to day 32 after which the germination fell off (Figure 2). There was no new seedling that emerged after day 34. Physical examination of the seeds at the end of 34 days germination period revealed that all the un-germinated seeds were rotten. Germination period ranged from 10 to 12 days but was not statistically different (
There were significant differences (
Population | Germination percentage (means ± SD) | Germination period (means ± SD) | Germination value (means ± SD) | Mean germination rate (means ± SD) | Final germination rate (means ± SD) | Germination index (means ± SD) |
---|---|---|---|---|---|---|
Ruaha | 63.4 ± 1.3b | 12 ± 1.02a | 1.03 ± 0.04a | 15.8 ± 3.06b | 0.06 ± 0.20b | 0.75 ± 0.31a |
Kigwe | 81.4 ± 2.4a | 11 ± 1.03a | 1.01 ± 0.02a | 20.3 ± 2.60a | 0.13 ± 0.37a | 0.96 ± 0.34b |
Tarangire | 72.1 ± 4.2c | 10 ± 0.62a | 1.03 ± 0.03a | 18.0 ± 4.00c | 0.12 ± 0.32a | 0.83 ± 0.26a |
There were significant correlations among some of the germination traits (Table 3). Germination value had a negative significant correlation with germination index (
3.2 Seedling growth
The first measurement of seedling height, root collar diameter and number of leaves was taken at the 30th day since germination. Seedlings from Kigwe and Tarangire populations exhibited more or less the same trend of gradual increase in shoot height (Figure 3A). Seedlings of all the three populations had similar trend of gradual increase in root collar diameter over time (Figure 3B). There was a similar steady increase in number of leaves bore by seedlings from Tarangire and Ruaha populations (Figure 3C).
Regardless of the population, there were significant differences (
Time period | Shoot height (cm) (means ± SD) | Root collar diameter (mm) (means ± SD) | Number of leaves (means ± SD) |
---|---|---|---|
Day 30 | 11.1 ± 2.8a | 12.4 ± 2.4b | 5.8 ± 1.6abd |
Day 45 | 11.4 ± 2.8ab | 14.3 ± 2.7a | 6.3 ± 1.8bef |
Day 60 | 11.8 ± 2.8ab | 15.4 ± 2.8a | 6.5 ± 1.9bdeg |
Day 90 | 12.8 ± 3.0c | 16.5 ± 3.0 ac | 6.5 ± 1.9cfg |
Day 105 | 13.2 ± 2.9c | 17.7 ± 2.9d | 6.6 ± 2.1bc |
There was no significant difference in shoot height between the three studied populations (
Population | Shoot height (cm) (means ± SD) | Root collar diameter (mm) (means ± SD) | Number of leaves (means ± SD) |
---|---|---|---|
Ruaha | 12.03 ± 3.0a | 16.35 ± 3.5a | 5.8 ± 1.7b |
Kigwe | 14.20 ± 3.2a | 18.13 ± 2.8a | 7.2 ± 1.4a |
Tarangire | 13.13 ± 2.4a | 18.17 ± 2.6a | 7.3 ± 1.8a |
Positive and significant correlations were observed among the evaluated seedling traits at the age of 303 days (Table 6). The lowest significant correlation was observed between shoot dry weight and root collar diameter (
Trait (Unit) | Shoot height | Root collar diameter | Number of course roots | Tap root length | Shoot fresh weight | Shoot dry weight | Root fresh weight | Root dry weight |
---|---|---|---|---|---|---|---|---|
Shoot height (cm) | ||||||||
Root collar diameter (mm) | 0.23 | |||||||
Number of course roots | 0.29 | 0.16 | ||||||
Tap root length (cm) | 0.06 | 0.23 | 0.02 | |||||
Shoot fresh weight (g) | 0.27 | 0.52** | 0.52** | 0.29 | ||||
Shoot dry weight (g) | 0.38* | 0.35* | 0.31 | 0.28 | 0.68*** | |||
Root fresh weight (g) | 0.32 | 0.55** | 0.30 | 0.54** | 0.63*** | 0.59*** | ||
Root dry weight (g) | 0.30 | 0.49** | 0.24 | 0.50** | 0.53** | 0.57*** | 0.97*** | |
Root to shoot ratio | 0.15 | 0.17 | −0.16 | 0.27 | 0.19 | −0.12 | 0.53** | 0.58*** |
Most of the evaluated seedling growth traits did not differ significantly (
Growth traits | Ruaha (means ± SD) | Kigwe (means ± SD) | Tarangire (means ± SD) |
---|---|---|---|
Shoot height (cm) | 15.1 ± 2.2a | 14.8 ± 1.9a | 14.6 ± 1.7a |
Root collar diameter (mm) | 19.2 ± 3.0a | 19.7 ± 3.8a | 20.9 ± 3.5a |
Number of course roots | 12 ± 3.4b | 10 ± 4.1a | 13 ± 6.2b |
Tap root length (cm) | 13.6 ± 3a | 13 ± 3.6a | 12.3 ± 3.4a |
Shoot fresh weight (g) | 26.9 ± 6.6b | 22.9 ± 9.7a | 28.8 ± 5.4b |
Shoot dry weight (g) | 3.5 ± 1.0a | 3.5 ± 2.2a | 3.6 ± 1.1a |
Root fresh weight (g) | 16.4 ± 8.2a | 16.8 ± 7.2a | 15.4 ± 8.8a |
Root dry weight (g) | 1.7 ± 1.2a | 1.8 ± 1.0a | 1.5 ± 1.2a |
Root to shoot ratio | 0.44 ± 0.2a | 0.6 ± 0.3a | 0.38 ± 0.2a |
4. Discussion
4.1 Variation in germination
This study has demonstrated the differences in germination traits in three populations of
The study species
Germination is an important factor in assessing the quality of any seed and determines early seedling performance and end products standard. In this study, seed cumulative germination percentage ranged from 63.4% to 81.4% indicating that the three populations possess quality seeds that can be used during domestication and tree improvement processes. The observed variation in germination percentage among the provenances is not attributed to differences in altitudes, environmental factors (day length, temperature, light quality, water availability and altitude), and climatic conditions of particular population, since this study was undertaken in one geographic location [19]. The results overall indicate that, maternal factors associated with individual seeds from each population could explain the observed variations [20]. It has been reported that position of seed in the fruit or tree and the age of the mother plant influence seed germination ability [21]. However in this study, such effects were not studied.
In this experiment no treatment was undertaken for germination of
4.2 Variation in seedling growth
Seedling traits including shoot height, root collar diameter, number of leaves, tap root length, total number of course roots per seedling, fresh and dry weights of all course roots and shoots variations are important determinants of seedlings to be planted in the field. This study has demonstrated that there are degrees of variation among various seedling growth traits suggesting that selection of any trait for improvement would be effective [18]. Number of leaves differed significantly among the three populations, with Kigwe and Tarangire having higher number of leaves than Ruaha, at 105 days (Table 5). Ruaha and Tarangire had higher number of course roots and shoot fresh weight than Kigwe population at 303 days (Table 7). Parker et al. [25] and Assogbadjo et al. [26] reported a positive influence of large seed size and seed reserve on the establishment and early growth of seedlings. So, higher seed width, weight and length might have contributed to the observed variation of
5. Conclusion
Acknowledgments
G. Ngatena, M. Said, R. Khalfani, P. Mmanda and J. Mtika assisted during fieldwork. Tanzania Forest Services Agency (TFS) supported data collection.
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