Provenance Variation in Seed, Seedling, and Early Growth Traits of Red Jabon (Neolamarckia macrophylla): An Endemic Species From Sulawesi and Maluku, Indonesia
Abstract
The availability of seed quality and tree growth information of red jabon (Neolamarckia macrophylla (Roxb.) Bosser) from different provenances is necessary to assess and optimize the utilization of its genetic resources. The research aimed to examine the variations in morphophysiological traits of seeds, seedlings, early tree growth, and pilodyn penetration of 10 red jabon populations from the Sulawesi (Konawe, Luwu Timur, Muna, Buton, Banggai, Wajo, Menado, and Lolayan) and Maluku (Tidore and Seram) regions. Analysis of variance was used to compare the performance of seed traits (fruit diameter, weight, seed length, seed width, seed weight, and germination capacity), seedling traits (seedling height and diameter), early growth traits (tree survival, height, diameter, and pylodin penetration) among provenances. The hierarchical cluster and principal component analysis were used to identify homogenous provenances based on similar traits. Provenances were significantly different (p < 0.05) for most fruit, seeds, seedlings, and early growth traits, except for seed weight, seedling sturdiness quotient, seedling height, tree diameter at 1 year, tree survival at 4 years, and pilodyn penetration. High genetic gain coupled with high heritability was found in seed length, seed width, tree diameter at 4 years, and tree volume at 4 years, indicating that these traits can be used to select the best provenances. The provenances can be grouped into two groups, namely the Sulawesi and Maluku regions. There are four subgroups in the Sulawesi region, while in the Maluku Islands region, two provenances (Seram and Tidore) are genetically relatively far apart. Seram provenance has the highest performance in seed morphophysiological traits and tree growth, so it is very promising for cultivation in similar provenance trial locations. These results are important in establishing seed sources, provenance selection, and other breeding activities.
1. Introduction
Plant morphological characterization is one method that can be used to recognize certain traits, distinguish between subspecies, and identify morphology. It is a low-cost functional complementary approach that does not require special equipment or technical expertise [1]. Morphological characteristics are commonly used to determine the diversity of plants, especially in the stem, fruit, seed, leaf, and flowers [2–4]. Information on the diversity of fruits, seeds, and seedlings’ growth and their correlation with geographic distribution and climatic factors is important for breeding activities [3, 5].
Variations in the morphology and physiology (phenotypic variance) of seeds and seedlings, apart from being influenced by environmental factors (geoclimate), are also controlled by genetic factors [3, 5]. Phenotypic variance (PV) is the total variation in phenotypes found across populations. Genotypic variance (GV) is the portion of PV that can be used as an attribute of genetic diversity between populations. In contrast, environmental variance (EV) is the portion of PV that is due to environmental influences [3, 6]. The magnitude of variation due to provenance (population) and environment, compared to the coefficient of provenance (genetic) variation and coefficient of environmental variation, was calculated for each related trait using the expected mean square of the genetic variance, EV, and the overall mean [7–9]. Different provenances may have differences in seed and seedling characteristics, as shown in many tree species, such as Anthocephalus cadamba [3], Cordia africana [10], Sterculia foetida [11], Toona sinensis [12], Juglans mandshurica [13], and Pongamia pinnata [14]. Climate variables (rainfall, temperature, and humidity), as well as longitude, latitude, and altitude, are factors that really influence the existence and morphology of a plant species [15]. Significant correlations between seed and seedling traits and specific geoclimatic factors were observed in several species [11, 16]. This correlation provides an indication that environmental factors influence plant morphology and physiology, as shown in Adansonia digitata [17], Tamarindus indica [18], Gmelina arborea [19], and Nothofagus glauca [20]. Morphological differences among provenances can be more precisely tested through provenance trials [21, 22]. Several studies have shown that differences in growth and wood quality between provenances are very important for the development of target species, such as Vachellia nilotica [23], Acacia mangium [24], and Neolamarckia cadamba [25]. This test is important to support forest restoration programs [26] and seed transfer guidelines [22].
The importance of seeds, seedlings, tree growth performance, and wood quality predicted through pilodyn penetration and their correlation with original geoclimatic factors will be studied on red jabon [Neolamarckia macrophylla (Roxb.) Bosser, synonym Anthocephalus macrophyllus (Roxb.) Havil., Rubiaceae family]. Red jabon is an Indonesian endemic fast-growing tree species naturally distributed in Sulawesi and Maluku Islands [27, 28]. It can grow in the lowlands up to 1000 m asl (above sea level), in various types of soil [29, 30], and is generally found in secondary forest areas, valleys, along rivers, and ridges [27]. The existence of ecological diversity in the natural distribution of red jabon allows for differences in the morphophysiology of seeds, seedlings, and their growth performance [3, 6, 8]. [32] found variations in the size of red jabon fruit and leaves between red jabon populations from Makassar and Menado (Sulawesi). The highest genetic variation of red jabon was reported between populations in three provenances in South Sulawesi [32]. Differences in growth were also reported in 55 families originating from Konami, South Sulawesi [33]. However, differences in the morphophysiology of seeds, seedlings, and their growth performance from all of their natural distributions (Sulawesi and Maluku Islands) have not been studied.
Red jabon wood has a strength class of II-III and a durability class of IV, which is widely used for particle board and light construction [29, 34]. This wood also has long fibers, and thin fiber wall thickness and is classified as a second-quality raw material for pulp and paper production [35]. The species has become of interest to the public, so that it is widely cultivated, especially for developing small plantation and community forests in Indonesia [36–38]. This condition requires the availability of high-quality seed sources from a wide range of population distribution with measurable genetic testing. However, until now, sources of genetically quality red jabon seeds are still unavailable [39]. The existing sources of red jabon seeds are only in the form of identified seed stands [40], while based on the Decree of the Minister of Environment and Forestry Number SK.707/Menhut-II/2013, red jabon is one of the tree species whose seeds must be taken from certified seed sources. Thus, initiating tree breeding activities involving diversity from a relatively wide growing distribution is required [41]. Therefore, the research aims to analyze the diversity of seeds and seedling traits, and the early growth performance as well as the extent of the contribution of genetic control and environmental factors to the diversity of these traits in 10 provenances from Sulawesi and Maluku Islands, Indonesia.
2. Materials and Methods
2.1. Materials
Ten provenances of red jabon on the islands of Sulawesi and Maluku were used for seed collection (Table 1, Figure 1). The location of the seed collection in Sulawesi region is a secondary natural forest, where red jabon generally grows side by side with other pioneer species, such as Neolamarckia cadamba, Duabanga moluccana, and Octomeles sumatrana. Meanwhile, on Seram and Tidore provenances (Maluku region), seed collection was carried out in primary natural forests. The provenance selection was based on information on growth distribution from the local Provincial Forestry Service and the Forest Tree Seed Center Region II, Ministry of Environment and Forestry, Indonesia. Based on the tree phenotype (grows well, straight trunk, healthy, and balanced canopy), 10–20 mother trees were selected from each provenance. The distance between mother trees was maintained at around 100 m to obtain optimal genetic variation [3, 42]. Each tree in each provenance was observed and measured for its tree height and diameter. The fruit was collected and extracted manually using the wet extraction method [3, 43]. Fruit and seed measurements and testing were carried out at the Seed Testing Laboratory, Institute for Environment and Forestry Standard and Instrument Implementation, Bogor. Climate data (precipitation) for 10 populations of red jabon was obtained from reports from the Central Statistics Agency (BPS) for each district in each province.
| Provenance (abbreviation) | Latitude; longitude | Altitude (m asl) | Precipitation (mm/year) | Average of temperature (°C) | Average of relative humidity (%) | Average of mother tree height (m) | Average of mother tree diameter (cm) |
|---|---|---|---|---|---|---|---|
| Konawe, Southeast Sulawesi (KSS) | 4°16′N−121°29′E | 129 | 2591 | 27.9 | 80.2 | 23.4 | 47.8 |
| Luwu Timur, South Sulawesi (LSS) | 2°22′N–120°12′E | 172 | 3109 | 27.7 | 79.9 | 20.7 | 46.7 |
| Muna island (MI) | 4°42′N–122°42′E | 45 | 2330 | 27.1 | 81.8 | 20.5 | 53.8 |
| Buton island (BI) | 5°08′N–122°81′E | 44 | 2353 | 27.5 | 80.6 | 27.7 | 53.1 |
| Banggai, Central Sulawesi (BCS) | 1°25′N–122°20′E | 33 | 1230 | 28.2 | 75.8 | 20.4 | 54.1 |
| Wajo, South Sulawesi (WSS) | 3°40′N–120°20′E | 41 | 2155 | 28.4 | 79.9 | 21.3 | 44.4 |
| Menado, North Sulawesi (MNS) | 1°56′S–124°30′E | 37 | 2852 | 27.3 | 79.7 | 19.3 | 50.0 |
| Lolayan, North Sulawesi (LNS) | 0°39′S–124°13′E | 350 | 2839 | 26.4 | 86.3 | 23.3 | 45.9 |
| Tidore island (TI) | 0°19′S–127°45′E | 333 | 2450 | 27.2 | 81.6 | 32.5 | 65.8 |
| Seram island (SI) | 3°05′S–129°04′E | 663 | 1917 | 27.9 | 83.5 | 36.0 | 72.3 |
2.2. Fruit and Seed Morphophysiological Traits
The characteristics of fruits and seeds measured in this study included fruit diameter, fruit weight, seed length, seed width, and seed weight. Fifty undamaged fruits were taken randomly from each provenance, and their diameter and weight were measured. Seeds from each provenance were composited, and 200 seeds were randomly taken from the composite seeds to measure their length and width using a light microscope (Zeiss Discovery V.8 stereo). Seed weight was determined by measuring 30 seeds for each provenance using analytical scales [3, 6].
2.3. Seedling Raising, Seedling Growth Performance, and Pilodyn Penetration
Seedling raising was carried out at the Nagrak Nursery Research Station, Center for the Implementation of Environmental and Forestry Standards and Instruments, Bogor (106°52′27″E, 6°36′74″S, 280 m asl). Seedlings were raised by sowing the seeds in an uncontrolled environment greenhouse (temperature of 29°C–34°C and relative humidity of 60%–75%) using a medium mixed with fine sand and soil (1:1 by volume) in the germination boxes while maintaining the identity of each provenance. The seedlings were transplanted into polybags measuring 10 cm in diameter and 15 cm in height and filled with a planting medium mixed with topsoil, compost, and husk charcoal (3:2:1 by volume) [3, 46]. Seedlings from each provenance were arranged in a completely randomized design (CRD) with 6 replications in the nursery. Each replication consisted of 25 seedlings arranged in a square (5 seedlings × 5 seedlings). After the seedlings were 4 months old, the seedlings representing each provenance were measured for total height, root collar diameter (RCD), and sturdiness quotient [3]. Sturdiness quotient is the ratio between height (in cm) and diameter (in mm). A high ratio indicates tall and thin seedlings, while a low ratio indicates sturdy seedlings [47].
The provenance trial was established at the Parung Panjang Forest Research Station, Bogor, West Java (06°23′09.226″S, 106°31′23.138″E, 52 m asl) using a randomized complete block design (RCBD) (Figure 1). The tests were carried out using 10 provenances (Table 1) with 6 planting blocks (replications). Each block consists of 25 individual seedlings per provenance. The planting site has relatively low soil fertility with a C-organic content of 1.92%, N-total 0.22%, P (Bray I) 13.75 ppm, Ca 2.75 cmol(+) kg−1, K 0.13 cmol(+) kg−1, CEC 24.42 cmol(+) kg−1, and pH 4.58. Annual precipitation, temperature, and relative humidity are 2990 mm per year, 28°C, and 80%, respectively. The initial plant spacing used was 3 × 3 m. The growth measurements were carried out at the age of 1 and 4 years after outplanting by measuring the total height using a scale pole and diameter of the stem base using a digital caliper (for 1-year-old plants) and phi-band (for 4-year-old plants). The measurement of diameter at the age of 1 year was carried out at a height of 20 cm above ground level, while the measurement of diameter at breast height (DBH) at 4 years old was carried out at 1.3 m above ground level. In addition, to estimate wood quality at 4 years old, each tree at the test location was measured for pilodyn penetration using Pilodyn (specification of pin diameter = 2.5 cm and strength = 6 J) [25, 48]. Pilodyn penetration is a nondestructive method for measuring the level of wood hardness, which is generally correlated with wood density [49]. Penetration was carried out at three points of the trunk at a height of 1.3 m [21] in a radial-horizontal manner with a distance between penetration points of 120° [50].
2.4. Data Analysis
Data were analyzed using analysis of variance (ANOVA) and Duncan’s multiple range test (DMRT) to test the significance of differences between the characteristics of the seed, seedling raising, tree growth performance, and pilodyn penetration to evaluate the wood quality using SPSS 26 software. Simple correlation (Pearson) was used to find the relationships between the characteristics of the seed, seedling, tree growth, and pilodyn penetration with mother tree height and diameter and geoclimatic factors (latitude, longitude, precipitation, temperature, relative humidity, and altitude).
Similarly, hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used to explain patterns of diversity between populations [3, 45]. PCA was also used to identify plant characters that contribute greatly to genetic diversity and group populations with the same seed, seedling, tree growth, and pilodyn penetration traits.
3. Results
A significant effect of provenance on the seed and seedling traits of red jabon was found in almost all traits except for seed weight (p = 0.074) and seedling sturdiness quotient (p = 0.078). The DMRT (α < 0.05) showed that the traits of fruits, seeds, and seedlings were significantly different between the 10 provenances of red jabon. Seedling height in the nursery (41.98%) and RCD in the nursery (40.21%) had the highest coefficient of variance (CV). The lowest CV was found in seed width (14.85%), followed by fruit diameter (15.39%) and seedling sturdiness quotient (16.96%) (Table 2). In the 1-year-old provenance trial at the Parung Panjang Forest Research Station, provenance only significantly affected tree height (p = 0.050) and had no significant effect on tree diameter (p = 0.305). At the age of 4 years, provenance differences significantly affected tree height (p = 0.001), tree diameter (p = 0.036), and tree volume (p = 0.033) but did not significantly affect pilodyn penetration (p = 0.156). Provenance also did not significantly affect the percentage of tree survival at the age of 4 years, with a range of tree survival percentage of 66% (LSS provenance) to 79% (TI provenance). Up to the age of 4 years, SI provenance had the best growth (tree height, diameter, and volume), followed by TI provenance (TI) (Figure 2).
| Provenance | Fruit diameter (cm) | Fruit weight (g) | Seed length (μm) | Seed width (μm) | Seed weight (mg) | Germination capacity (%) | Seedling height (cm) | Seedling diameter (cm) | Sturdiness quotient |
|---|---|---|---|---|---|---|---|---|---|
| KSS | 4.78ab | 42.03bc | 159.46ab | 107.77b | 0.0062ab | 65.3bc | 24.54c | 3.00b | 8.28 |
| LSS | 3.85d | 35.66d | 151.58b | 102.92b | 0.0047b | 53.0cd | 27.09bc | 3.34ab | 8.17 |
| MI | 4.66ab | 39.84bc | 127.31d | 91.03c | 0.0055ab | 46.0d | 26.34bc | 3.24ab | 8.16 |
| BI | 4.21c | 39.56bc | 156.89ab | 107.51b | 0.0064ab | 56.0cd | 26.79bc | 3.19ab | 8.39 |
| BCS | 4.50bc | 40.94bc | 151.58b | 105.53b | 0.0059ab | 68.0bc | 28.11ab | 3.35a | 8.34 |
| WSS | 4.63ab | 38.47cd | 154.01ab | 98.64bc | 0.0057ab | 58.8cd | 29.24ab | 3.44a | 8.42 |
| MNS | 4.71ab | 42.78b | 140.43c | 101.43b | 0.0060ab | 77.0ab | 27.32abc | 3.26ab | 8.44 |
| LNS | 4.61ab | 40.36bc | 153.62ab | 103.49b | 0.0061ab | 68.0bc | 27.86ab | 3.43a | 8.12 |
| TI | 4.59b | 41.56bc | 153.67ab | 107.82b | 0.0071a | 75.5ab | 30.51a | 3.50a | 8.61 |
| SI | 4.99a | 48.36a | 165.32a | 118.67a | 0.0074a | 86.0a | 28.27ab | 3.36a | 8.40 |
| Mean | 4.58 | 40.86 | 151.98 | 103.45 | 0.0063 | 65.36 | 27.80 | 3.32 | 8.35 |
| Min–max | 2.76–7.28 | 21.06–71.41 | 92.00–234.10 | 14.70–183.10 | 0.0030–0.0130 | 26.00–95.00 | 9.33–99.73 | 1.08–9.99 | 3.04–11.82 |
| SD | 0.705 | 7.302 | 22.57 | 18.06 | 0.0016 | 14.36 | 12.58 | 1.33 | 1.41 |
| CV (%) | 15.39 | 17.87 | 14.85 | 17.46 | 26.54 | 21.98 | 41.98 | 40.21 | 16.96 |
| F-test | 7.311∗∗ | 8.435∗∗ | 8.216∗∗ | 6.205∗∗ | 1.866ns | 6.904∗∗ | 2.907∗∗ | 2.096∗ | 1.726ns |
| p-value | p ≤ 0.001 | p ≤ 0.001 | p ≤ 0.001 | p ≤ 0.001 | p = 0.074 | p ≤ 0.001 | p = 0.002 | p ≤ 0.05 | p = 0.078 |
- Note: Different letters within a column indicate significant differences at p < 0.05. BI = Buton Island, Southeast Sulawesi, LSS = Luwu Timur, South Sulawesi, MI = Muna Island, Southeast Sulawesi, SI = Seram Island, Maluku, TI = Tidore Island, Maluku.
- Abbreviations: BCS = Banggai, Central Sulawesi, KSS = Konawe, Southeast Sulawesi, LNS = Lolayan, North Sulawesi, MNS = Menado, North Sulawesi, ns = nonsignificant, SD = Standard deviation, WSS = Wajo, South Sulawesi.
- ∗significant at 5%.
- ∗∗significant at 1%.
In general, those from SI provenance showed the highest performance, followed by those from TI provenance. The SI provenance has the highest performance in 9 traits, that is, fruit diameter, fruit weight, seed length, seed width, seed weight, germination capacity, tree height at 4 years, tree diameter at 4 years, and tree volume at 4 years. Meanwhile, the SI provenance has maximum values for seedling height, seedling diameter, tree height at 1 year, and tree survival at 4 years (Table 2, Figure 2).
Differences in seed morphophysiology, seedling growth, and early tree growth in the field between provenances show that this variability is influenced by genetic and environmental factors. Our study found that phenotypic variation ranged from 1212.55 (seed length) to 0.00315 (seed weight), and environmental variation ranged from 432.42 (seed length) to 0.0025 (seed weight), while genotypic variation ranged from 780.13 (seed length) to 0.00056 (seed weight). The highest phenotypic coefficient of variance (PCV), ECV, and GCV were seed length, that is, 34.84, 20.79, and 27.93, respectively. Minimum PCV, ECV, and GCV were associated with seed weight (0.0177, 0.0161, and 0.0075, respectively). Several traits, such as the seedling diameter and height, sturdiness quotient in the nursery, tree height and diameter at 1 year, tree survival at 4 years, and pilodyn penetration, had a higher ECV than a GCV, which indicated that the environment contributed quite significantly to early seedling growth. Meanwhile, for seed traits (seed length, seed width, seed weight, germination capacity), tree height at 4 years, tree diameter at 4 years, and tree volume at 4 years, GCV was proven to be higher than ECV (Table 3). This shows that most of the seed traits and tree growth at 4 years are more influenced by genetics.
| Traits | PV | EV | GV | PCV | ECV | GCV | h2b | GG (%) |
|---|---|---|---|---|---|---|---|---|
| FD (cm) | 1.1101 | 0.4307 | 0.6794 | 1.053 | 0.656 | 0.824 | 0.61 | 29.01 |
| FW (g) | 128.739 | 45.033 | 83.715 | 11.346 | 6.711 | 9.149 | 0.65 | 37.19 |
| SL (μm) | 1212.55 | 432.42 | 780.13 | 34.82 | 20.79 | 27.93 | 0.64 | 204.44 |
| SW (μm) | 664.93 | 288.94 | 375.98 | 25.78 | 16.99 | 19.39 | 0.56 | 166.32 |
| SWG (mg) | 0.00315 | 0.00056 | 0.0025 | 0.0018 | 0.0016 | 0.0008 | 0.17 | 10.19 |
| GC (%) | 213.13 | 86.08 | 127.05 | 14.59 | 9.27 | 11.27 | 0.59 | 27.42 |
| SH (cm) | 221.22 | 149.80 | 221.22 | 14.87 | 12.24 | 8.45 | 0.32 | 35.57 |
| SD (mm) | 2.162 | 1.697 | 0.465 | 1.471 | 1.303 | 0.682 | 0.21 | 19.59 |
| SSQ | 2.347 | 1.986 | 0.360 | 1.532 | 1.409 | 0.600 | 0.15 | 5.80 |
| TH-1 (m) | 0.487 | 0.398 | 0.089 | 0.698 | 0.632 | 0.297 | 0.18 | 19.28 |
| TD-1 (cm) | 1.873 | 1.793 | 0.079 | 1.368 | 1.339 | 0.283 | 0.04 | 4.45 |
| TS-4 (%) | 111.45 | 105.76 | 5.70 | 10.55 | 10.28 | 2.38 | 0.05 | 1.51 |
| TH-4 (m) | 10.95 | 4.62 | 9.54 | 3.31 | 2.15 | 2.52 | 0.57 | 41.31 |
| TD-4 (cm) | 22.36 | 4.67 | 17.73 | 4.72 | 2.15 | 4.21 | 0.79 | 56.46 |
| V-4 (m3) | 0.0095 | 0.0019 | 0.0075 | 0.097 | 0.044 | 0.086 | 0.79 | 136.11 |
| PP-4 (cm) | 6.533 | 5.848 | 0.684 | 2.556 | 2.418 | 0.827 | 0.11 | 1.87 |
- Note: SWG = seed weight, SDN = seedling diameter, SHN = seedling height, TH-1 = tree height at 1 year, SDF = tree diameter at 1 year, TS-4 = tree survival at 4 years, TH-4 = tree height at 4 years, TD-4 = tree height at 4 years, PP-4 = pilodyn penetration at 4 years, PV = phenotypic variance, h2b = broad sense heritability.
- Abbreviations: ECV = environment coefficient of variance, EV = environment variance, FD = fruit diameter, FW = fruit weight, GC = germination capacity, GCV = genotypic coefficient of variance, GG = genetic gain, GV = genotypic variance, PCV = phenotypic coefficient of variance, SL = seed length, SSQ = seedling sturdiness quotient, SW = seed width.
Heritability estimates ranged between 0.04 (tree height at 1 year) and 0.79 (tree diameter and volume at 4 years). Estimates of GG range from 1.51% (tree survival at 4 years) to 204.44% (seed length). High GG coupled with high heritability was found in seed length, seed width, tree diameter at 4 years, and tree volume at 4 years. In contrast, the low GGs and heritability pair were found in seed weight, seedling sturdiness quotient, tree survival, and tree diameter at 1 year (Table 3). High heritability values paired with high GG indicate that these traits can be used to select the best populations.
Several traits of seeds, seedlings, and tree growth have significant correlations with each other. The fruit diameter was positively significantly correlated (p ≤ 0.05) with fruit weight (r2 = 0.815) and seed weight (r2 = 0.826), while fruit weight was also positively correlated (p < 0.05) with germination capacity (r2 = 0.817) and tree height at 4 years (r2 = 0.747). Seed length was significantly negatively correlated (p ≤ 0.05) with seedling growth in the nursery but different from seed width, which was positively correlated with seedling height in the nursery (r2 = 0.671). Seedling height and diameter in the nursery were generally significantly positively correlated with tree growth at 1 year (tree height and diameter) and 4 years (tree diameter and volume). Pilodyn penetration tended to be negatively correlated (p ≤ 0.05) with tree growth and was clearly shown to have a negative correlation with tree height at 4 years (r2 = −0.670) (Table 4).
| FD | FW | SL | SW | SWg | GC | SH | SD | SQ | TH1 | TD1 | TS4 | TH4 | TD4 | V4 | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| FW | 0.815∗∗ | ||||||||||||||
| SL | 0.020 | −0.093 | |||||||||||||
| SW | −0.083 | 0.136 | −0.679∗ | ||||||||||||
| SWg | 0.643∗ | 0.826∗∗ | −0.320 | 0.419 | |||||||||||
| GC | 0.591 | 0.817∗∗ | −0.473 | 0.183 | 0.759∗ | ||||||||||
| SH | 0.060 | 0.081 | −0.761∗ | 0.671∗ | 0.352 | 0.391 | |||||||||
| SD | −0.053 | −0.058 | −0.638∗ | 0.609 | 0.132 | 0.255 | 0.931∗∗ | ||||||||
| SQ | 0.265 | 0.375 | −0.679∗ | 0.419 | 0.628 | 0.549 | 0.596 | 0.269 | |||||||
| TH-1 | 0.075 | 0.091 | −0.477 | 0.682∗ | 0.404 | 0.265 | 0.862∗∗ | 0.851∗∗ | 0.339 | ||||||
| TD-1 | −0.406 | −0.259 | −0.687∗ | 0.551 | −0.129 | 0.104 | 0.783∗∗ | 0.787∗∗ | 0.378 | 0.588 | |||||
| TS-4 | 0.365 | 0.341 | −0.534 | 0.435 | 0.495 | 0.358 | 0.579 | 0.302 | −0.851∗∗ | 0.319 | 0.308 | ||||
| TH-4 | 0.558 | 0.747∗ | −0.180 | 0.343 | 0.757∗ | 0.647∗ | 0.435 | 0.331 | 0.426 | 0.516 | 0.149 | 0.277 | |||
| TD-4 | 0.441 | 0.412 | −0.479 | 0.567 | 0.512 | 0.411 | 0.807∗∗ | 0.684∗ | 0.601 | 0.750∗ | 0.538 | 0.668∗ | 0.731∗ | ||
| V-4 | 0.510 | 0.561 | −0.458 | 0.553 | 0.654∗ | 0.587 | 0.796∗∗ | 0.706∗ | 0.543 | 0.772∗∗ | 0.447 | 0.551 | 0.851∗∗ | 0.948∗∗ | |
| PP-4 | −0.194 | −0.367 | −0.185 | −0.167 | −0.171 | −0.211 | −0.174 | −0.354 | 0.297 | −0.344 | −0.142 | 0.283 | −0.670∗ | −0.386 | −0.538 |
- Note: See Table 3 for information of parameters of seed, seedling, and tree growth.
- ∗Significant at p ≤ 0.05.
- ∗∗Significant at p ≤ 0.01.
Mother tree height was generally not correlated with seed and seedling traits and initial tree growth, while mother tree diameter was positively correlated (p ≤ 0.05) with fruit weight (r2 = 0.737), seed width (r2 = 0.680), seed weight (r2 = 0.787), and germination capacity (r2 = 0.690). The average temperature and relative humidity did not show a significant correlation with the seeds, seedlings traits, and the early growth performance of red jabon. Annual precipitation had a significant positive correlation (p ≤ 0.05) with tree height (r2 = 0.771) and volume of 4-year-old trees (r2 = 0.687). Meanwhile, other geoclimatic factors such as longitude were positively correlated (p < 0.05) with fruit weight (r2 = 0.849), seed weight (r2 = 0.883), germination capacity (r2 = 0.807), tree height at 4 years (r2 = 0.840), and tree volume at 4 years (r2 = 0.676). Altitude also recorded a significant positive correlation (p ≤ 0.05) with seed weight (r2 = 0.702), tree height (r2 = 0.802), tree diameter (r2 = 0.650), and volume at 4 years (r2 = 0.715). Most seeds, seedlings, and early growth traits were not significantly correlated with geoclimatic factors (Table 5).
| Traits | Mother tree height | Mother tree diameter | Precipitation | Average of temperature | Average of relative humidity | Latitude | Longitude | Altitude |
|---|---|---|---|---|---|---|---|---|
| FD (cm) | 0.326 | 0.411 | −0.215 | 0.005 | 0.285 | −0.051 | 0.591 | 0.146 |
| FW (g) | 0.639∗ | 0.737∗ | −0.233 | 0.037 | 0.257 | 0.268 | 0.840∗∗ | 0.536 |
| SL (μm) | 0.081 | 0.397 | −0.163 | 0.227 | 0.025 | 0.237 | 0.554 | 0.515 |
| SW (μm) | 0.040 | 0.680∗∗ | −0.189 | −0.336 | 0.173 | 0.236 | 0.563 | 0.415 |
| SWGt (mg) | 0.147 | 0.787∗∗ | −0.332 | −0.064 | 0.334 | 0.090 | 0.883∗∗ | 0.702∗ |
| GC (%) | 0.150 | 0.690∗ | −0.195 | 0.018 | 0.173 | 0.578 | 0.807∗∗ | 0.468 |
| SHN (cm) | −0.093 | 0.404 | −0.255 | 0.020 | 0.076 | 0.370 | 0.395 | 0.210 |
| SDN (mm) | −0.018 | 0.251 | −0.128 | −0.136 | 0.223 | 0.485 | 0.279 | 0.176 |
| SSQ | −0.161 | 0.522 | −0.284 | 0.316 | −0.269 | 0.052 | 0.474 | 0.178 |
| TH-1 (m) | 0.033 | 0.470 | −0.413 | −0.027 | 0.214 | 0.213 | 0.400 | 0.367 |
| TD-1 (cm) | 0.080 | 0.214 | −0.105 | 0.205 | −0.276 | 0.537 | 0.040 | −0.047 |
| TS-4 (%) | −0.380 | 0.421 | −0.495 | 0.271 | −0.310 | −0.156 | 0.343 | −0.013 |
| TH-4 (m) | −0.195 | 0.367 | 0.771∗∗ | 0.263 | 0.055 | 0.704∗ | 0.860∗∗ | 0.820∗∗ |
| TD-4 (cm) | 0.296 | 0.199 | 0.521 | 0.124 | 0.284 | 0.243 | 0.529 | 0.652∗ |
| V-4 | 0.192 | 0.350 | 0.687∗ | 0.027 | −0.538 | 0.478 | 0.676∗ | 0.715∗ |
| PP-4 (mm) | −0.442 | −0.433 | 0.469 | 0.005 | 0.285 | −0.513 | −0.384 | −0.573 |
- Note: See Table 3 for information of parameters of seed, seedling, and tree growth.
- ∗Significant at p ≤ 0.05.
- ∗∗Significant at p ≤ 0.01.
HCA and PCA biplot showed the same tendency in classifying genotypes based on seeds, seedlings, and early growth traits of red jabon originating from the Sulawesi and Maluku Islands. Close geographic distance between populations generally places provenances within the same group and is relatively close genetically. There are two large groups, namely provenances from the Sulawesi Islands and provenances from the Maluku Islands. In the Sulawesi Islands provenances group, there are also 4 subgroups, that is, subgroup 1 consists of four provenances (BCS, LNS, LSS, and WSS), subgroup 2 consists of 2 provenances (BI, MI), and subgroup 3 and subgroup 4 consist of only one provenance, that is, KSS and MNS, respectively. Meanwhile, the Maluku Islands group places two provenances that are genetically relatively far apart, that is, TI and SI (Figure 3).
4. Discussion
Differences in provenance or geographic origin of red jabon had a significant effect on most seeds, seedlings, and tree growth traits. Variations in seed and seedling traits have been studied in several tree species, such as Cordia africana [10, 41], Suaeda aralocaspica [5], Pinus wallichiana [6], Cedrus deodara [53], Faidherbia albida [42], Anthocephalus cadamba [3], Gmelina arborea [19], Sterculia foetida [11], Toona sinensis [12], and Juglans mandshurica [13]. Seed, seedling, and tree growth traits are interdependent and controlled by genetics, environmental influences, and seed characteristics. Variations in the seeds and seedling traits between red jabon provenances are most likely caused by natural constraints in their geographical locations. Differences in growth between provenance trials of forest trees have been widely reported in several species, such as Eucalyptus tereticornis [54], Araucaria cunninghamii [55], Acacia mangium [24], and Picea abies [56]. The existence of red jabon in various habitats with diverse geoclimatic conditions can form different genetic compositions between populations. In this study, SI provenance has the highest performance in 9 traits, including seed physical and physiological traits and tree growth, so it has great potential for cultivation, especially in environmental conditions in Parung Panjang Bogor and other similar locations.
Our study found that GCV for seed traits (seed length, seed width, seed weight, germination capacity), tree height at 4 years, tree diameter at 4 years, and tree volume at 4 years were higher than ECV. The error variance is relatively low compared to the genotype variance for these traits, causing PCV and GCV to be close to these traits. The results indicate that the genotypic component of these traits is the main contributor to the total variance of these traits [5, 7, 11]. Meanwhile, ECV for seedling diameter and height, sturdiness quotient, tree height at 1 year, diameter at 1 year, tree survival at 4 years, and pilodyn penetration at 4 years was higher than GCV. These results showed that the contribution of environmental factors is greater than genetic factors in determining the diversity of the initial growth of seedlings, tree survival, and pilodyn penetration at 4 years. The genetic influence is thought to have not been expressed in the early stages of growth (seedling level and 1 year of age in the field), so the genetic influence is still low. This is in line with [57] who stated that the expression of genetics may depend on the provenance and age of the individuals. Similar results were also found in the provenance–progeny test of Larix kaempferi [58] and Araucaria angustifolia [59], where in the early stages of growth, the genetic influence was relatively low.
The variability between provenances shows its great potential for selection in tree improvement programs. In this study, high values of GCV and GG were found in seed length, seed width, seed weight, germination capacity, tree height at 4 years, tree diameter at 4 years, and tree volume at 4 years. A high GCV will increase the effectiveness of selection on this trait, while a high GG indicates that provenance has a large influence on this trait, and selection activities will produce a better genotype or higher productivity [3, 6]. In most tree species, the morphophysiological characteristics of seeds and seedlings are strongly influenced by genotypic factors, while environmental factors, which vary according to location and population in a location, only have a small influence [60]. Genetic control of seed size, weight, and germination characteristics has also been found in other tree species such as Calophyllum inophyllum [61], Anthocephalus cadamba [3], and Cordia africana [10]. Meanwhile, genetic control on growth between provenances has also been widely reported [25, 58, 59].
Several parameters, such as fruit diameter, fruit weight, seed length, seed weight, germination capacity, seedling height, tree height at 4 years, tree diameter at 4 years, and tree volume at 4 years, have high heritability (> 0.3) [62]. Heritability is often used as an indicator in the selection of one or more traits [63, 64]. High heritability values paired with high GG were found in seed length, seed width, tree diameter at 4 years, and tree volume at 4 years. This indicates that these traits are of high genetic origin, with a large number of additive genetic components that can be inherited and can be used to select the best populations for improving species characteristics. Rawat and Bakshi [6] observed that high heritability values, accompanied by GGs, make it more appropriate to select the best individuals from the best origins. Meanwhile, if the heritability value is high but the GG is low, then the trait contains more nonadditive genetic components than additive genetic components.
Several characteristics of fruit, seed, seedling, and early growth of trees have a significant correlation with each other (Table 4). Fruit weight and seed weight have a significant positive correlation with germination capacity, indicating that fruits and seeds that are heavier in weight have higher germination capacity. Likewise, seed width correlated with seedling height and tree growth at 1 year. The influence of seed size and weight on germination and seedling growth was also found in Gmelina arborea [19], Cordia africana [10], and Prosopis cineraria [65]. Seedling traits have a positive correlation with growth performances in the provenance (field) test. In this study, seedling height and diameter have a positive correlation with tree height and diameter at 1 year, and tree diameter and volume at 4 years. These results are supported by other previous studies where seedling height in nursery is significantly correlated with seedling height in the field [66–68]. In addition, a negative correlation was also found in seedling sturdiness quotient and tree survival at 4 years. The more robust seedlings (lower sturdiness quotient) can increase seedling growth performance and adaptation potential, and result in higher tree survival [68, 69].
Variations in seed traits, such as morphology and seed weight between populations of a plant species, may be controlled by environmental or geographic variables [70–72]. Various studies show that climate variables (precipitation, temperature, and humidity) and altitude of the seed origin are factors that have a significant influence on the existence and morphology of a plant species [3, 72, 73]. However, our study found that most of the geoclimatic variables had no effect on the seed and seedling traits, except longitude, which was significantly correlated with seed weight and germination capacity, and altitude, which was significantly correlated with seed weight. Increasing longitude correlates with increasing seed weight and germination capacity. The tendency of longitude to influence seed morphophysiology has also been reported in Anthocephalus cadamba [3] and Pinus wallichiana [6], which is thought to be related to rainfall intensity [3, 6]. The influence of longitude is also thought to be related to the intensity of red jabon wood utilization. Furthermore, red jabon in the Sulawesi region is also more popular for various purposes such as construction, furniture, and other uses, so its exploitation is also higher than in the Maluku region. This condition affects the fragmented population and availability of mother trees (mother trees in the Maluku region are higher with a larger diameter). The availability of the mother tree will further affect the quality of the seeds, including weight and seed germination. This can be seen from the positive correlation of the diameter of the mother tree with fruit weight, seed width, seed weight, and germination capacity (Table 5). J. M. Baskin and C. C. Baskin [74] stated that the mother tree has a greater influence on seed traits, especially seed germination or dormancy. Seeds collected from Maluku (Seram and Todore provenances) also produced better growth in tree height and volume at the provenance trial. This is indicated by a significant positive correlation between longitude and tree height and volume. In addition, seeds from higher elevations produce better tree growth. In general, under natural growth conditions, trees at high altitudes (mountains) tend to have lower tree heights than similar trees in the lowlands [75]. Still, in this study, the maximum altitude of seed origin (provenance) was only 663 m asl, so the climate conditions were not significantly different from the provenance trial location. Precipitation and temperature are important controlling factors for tree height diversity [76]. In addition, provenances with high altitudes are located on Seram and Todore Islands, which are primary natural forest populations (other locations are secondary natural forests) with better mother quality, so obtaining genetically better seeds is possible.
In general, HCA and PCA showed that SI and TI provenances from the Maluku region have the highest genetic distance and are separated from other provenances from Sulawesi. Provenances originating from the Maluku region are expected to have higher genetic purity (true provenance) compared to provenance originating from the Sulawesi region. Furthermore, as red jabon in the Sulawesi region has been widely cultivated [26], there is a possibility that a mixture of origin in subgroup 1 (BCS, LNS, LSS, WSS) and subgroup 2 (MI, BI) has occurred. Genetic mixing due to seed transfer (gene flow) between cultivated trees and wild trees also occurs in the populations of Anthocephalus cadamba [77] and Castanea sativa [78]. The maximum intracluster distance also revealed that MNS and KSS provenances have greater genetic distances than others in the Sulawesi region. This indicates the great potential for cross-breeding these provenances with others to enrich genetic diversity in the next generation. Crossing between parents with wide genetic distances (different clusters) will produce maximum heterosis and wide variability in the genetic structure of the offspring [78, 79].
5. Conclusion
Seed and seedling traits are interdependent and controlled by genetic and environmental influences. Most seeds, seedlings, and tree growth performance traits of red jabon in provenance trials showed that their genetic diversity was strongly influenced by genetic factors. In contrast, the growth characteristics of seedlings and early tree growth (at 1 year old) were more influenced by environmental factors. There was a significant correlation between longitude and the characteristics of seed weight, germination capacity, and tree growth at 4 years old. Increasing longitude correlates with increasing seed weight and seed germination and also influences the better growth of 4-year-old trees. High heritability values paired with high GG were found in seed length, seed width, tree diameter at 4 years, and tree volume at 4 years, indicating that the traits are more appropriate for selecting the best individuals from the best origins. Population grouping showed that the Tidore and Seram provenances have a wide genetic distance, so the diversity of the two provenances is higher than the provenance from the Sulawesi region. Seram provenance has the highest performance in seed morphophysiological and tree growth traits, so it has great potential for cultivation, especially in environmental conditions similar to the provenance trial location. This information is important in developing breeding strategies to improve the quality of red jabon seeds and seedlings in Indonesia.
Disclosure
The funder had no role in the design of the study, in the collection, analysis, or interpretation of data, in the writing of manuscript, or in the decision to publish result.
Conflicts of Interest
The authors declare no conflicts of interest.
Funding
This research was supported by Lembaga Pengelola Dana Pendidikan ∗ B-1738/II.7.5/FR/11/2022.
Acknowledgments
The authors would like to acknowledge Forest Tree Seed Technology Research and Development Institute, Bogor, Indonesia, for the provision of field test facilities (provenance trial) and BRIN (National Research and Innovation Agency, Republic of Indonesia) for laboratory facilities, and LPDP (Education Fund Management Institution-Ministry of Finance, Republic of Indonesia) for their financial assistance.
Open Research
Data Availability Statement
The datasets on this study are available from the corresponding author on reasonable request.
