The oil palm (Elaeis guineensis Jacq.) is the most productive oil-bearing crop worldwide, contributing substantially to global food security and sustainable economic development (Ooi et al., 2016). In Ghana, oil palm is a major commercial tree crop with the capacity to sustain high yields for more than 25 years. Yields typically peak around eight years after planting but begin to decline between 16 and 18 years, largely due to challenges associated with harvesting and maintaining optimal frond numbers as palms increase in height (Mathews et al., 2006; Lee et al., 2019; Amiru et al., 2021).
       
The development of cultivars with reduced height increment has been identified as a strategic intervention to extend plantation lifespan, lower harvesting costs and facilitate mechanization. Previous studies have reported oil palm germplasm with favorable vegetative traits for height control (Seng et al., 2015). In Ghana, populations of putative dumpy palms derived from UR555/1545D×UR555/1301, exhibiting annual height increments of 15-20 cm (7.5-9.8 m at 49 years), have been identified at the CSIR-Oil Palm Research Institute. These dwarf cultivars represent a significant advancement in breeding, combining high oil yields with compact growth forms that enable easier harvesting, higher planting densities and improved economic sustainability compared to traditional tall varieties.
       
Oil palm is an outbreeding, heterozygous species, resulting in extensive genetic variability within hybrid progenies (Cochard et al., 2005; Teh et al., 2019). This variability provides opportunities for breeders to select elite individuals with superior agronomic traits (Nakkaew, 2024). Early screening for genetic variability at the nursery stage typically between 3 and 12 months allows for the identification and elimination of suboptimal or illegitimate seedlings prior to field transplantation (Teh et al., 2019). Estimation of genetic variability parameters and heritability for traits such as plant height is therefore critical in the selection of dwarf and high-yielding varieties (Tupaz-Vera et al., 2021).
       
Understanding the temporal expression of genetic variability is essential for effective selection strategies in breeding programs. Growth traits such as plant height, leaf number, leaf area and biomass accumulation serve as key indicators of vigor and productivity. Evaluating genotypes across multiple growth stages provides insights into trait stability, gene action and selection efficiency. Against this background, the present study aims to evaluate eleven genotypes across four growth stages (3, 4.5, 6.5 and 8.5 months after transplanting, MAT) to assess genetic variability, heritability and selection potential for growth and biomass-related traits.

The study involved progenies derived from crosses between selected high-yielding elite Dura mother palms and putative dwarf palms. The elite Dura palms served as the female parents, while the putative dwarf palms were used as male parents to generate the experimental genotypes. The study was carried out between October 2024 and December 2025. The site is located at 164 m above sea level, between latitudes 06°02′-06°05′ N and longitudes 00°52′-00°54′ W. It receives about 1425 mm of rainfall annually, with a bimodal pattern: a major rainy season from April to July and a minor one from September to mid-November. Temperatures remain fairly stable year-round, ranging from 24°C to 30°C.The experiment was arranged in a randomized complete block design (RCBD) with four replications. The treatments consisted of eleven oil palm genotypes (G1-G11). Each genotype was represented by 12 seedlings per replication, resulting in a total of 528 seedlings (11 genotypes × 4 replications × 12 plants) planted in 28 cm × 36 cm × 47 cm polybags filled with topsoil. Seeds were first raised in pre-nursery polybags under partial light, then transplanted after four months into larger nursery bags with intact soil balls. Soil was firmed and surfaces mulched with sawdust to conserve moisture.
       
Data collection began when seedlings were five months old, with observations taken at 3, 4.5, 6.5 and 8.5 months after transplanting. Twelve seedlings per treatment per replication were tagged for measurement. The recorded parameters included: Plant height (PH): measured from soil surface to the tip of the longest leaf. Number of leaves (NL): counted as fully expanded leaves per plant. Leaf area (LA): estimated non-destructively using leaflet length and width, applying a correction factor (0.57) in the formula.
 

A=b(nlw)

 
Where,
A = Leaf area = correction factor (0.57).
n = Number of leaves.
lw = Mean product of length and width of the sampled leaflets.
       
Basal circumference (BC): measured with digital calipers at 0.5 cm above soil, with circumference calculated as C=πd.
       
Biomass was assessed through destructive sampling at 4.5 and 8.5 months after transplanting. One uniform seedling per genotype per replication was randomly selected. Polybags were cut open to remove the soil cluster, which was soaked for 30 minutes to loosen soil before roots were gently washed. Plants were separated into roots, butt and fronds, chopped into smaller pieces and oven-dried at 105/°C until constant weight. Dry weights of root, shoot, basal and total biomass were then recorded. Growth and biomass data were analyzed using ANOVA under the RCBD in Genstat, with treatment means separated by the LSD test at the 5% level. Genetic variability parameters, including genotypic and phenotypic variances, were estimated and GCV and PCV were calculated to assess variability among genotypes. Broad-sense heritability and genetic advance were computed in R using the variability package to evaluate selection potential. Correlation analysis was performed to examine relationships between vegetative traits and biomass accumulation.

Genetic variability and growth dynamics
 
The analysis of variance revealed highly significant genotypic differences (p≤0.001) for most vegetative growth traits across the different developmental stages evaluated (Tables 1-4). The presence of significant variation among the evaluated genotypes indicates the existence of substantial genetic diversity within the breeding population, which is essential for effective selection and genetic improvement in oil palm breeding programs. High levels of genetic variability are essential for effective selection and long-term genetic improvement in oil palm breeding programs (Arolu et al., 2019; Latif et al., 2021; Barcelos et al., 2019). Similar observations were reported, where significant genotypic variability was considered fundamental for effective selection and breeding progress (Kumar et al., 2026; Singh et al., 2023). At 4.5 MAT, genotypes such as G7 demonstrated outstanding biomass accumulation and structural development, followed by G1 and G3, suggesting that these genotypes possess superior early vigor and growth efficiency (Table 2). Early vegetative vigor is an important determinant of seedling establishment and future productivity in oil palm plantations (Corley and Tinker, 2016; Murphy, 2019).








       
At later developmental stages (6.5-8.5 MAT), genotypic differences remained highly significant for major growth traits (Tables 3 and 4). Genotypes G1, G7, G3 and G11 consistently maintained superior performance across stages, indicating stability in growth expression. In contrast, genotype G10 consistently recorded the lowest means across traits, suggesting comparatively limited growth potential under the experimental conditions. Stability in vegetative performance across developmental stages is a desirable attribute in breeding programs aimed at improving plantation productivity and adaptation (Barcelos et al., 2019; Singh et al., 2020).
       
Across all growth stages, phenotypic variance exceeded genotypic variance, resulting in PCV values consistently higher than GCV for all traits. This pattern suggests that environmental factors influenced phenotypic expression; however, the relatively small differences between PCV and GCV for several traits indicate that a substantial proportion of the observed variability is genetically controlled. Similar patterns have been reported in oil palm genetic studies where environmental conditions influence phenotypic expression but do not obscure underlying genetic variability among genotypes (Swaray et al., 2021; Arolu et al., 2019; Cros et al., 2018).
 
Variability in vegetative growth traits
 
Among the evaluated traits, leaf area consistently exhibited the highest levels of variability, as indicated by comparatively large GCV and PCV values across growth stages. High variability in leaf area suggests substantial genetic diversity among the genotypes with respect to canopy development. In perennial crops such as oil palm, large leaf area enhances photosynthetic surface area and improves light interception, thereby increasing assimilate production and biomass accumulation (Murphy, 2019; Rival and Jaligot, 2020; Woittiez et al., 2017). Plant height also displayed moderate to high variability throughout the experimental period. Variation in plant height among oil palm genotypes is frequently associated with differences in vigor, growth efficiency and genetic background. High variability in plant height has been widely reported in oil palm germplasm collections and contributes significantly to phenotypic divergence among genotypes (Barcelos et al., 2019; Laha et al., 2025).
 
Heritability of growth traits
 
Broad-sense heritability estimates revealed substantial differences in the degree of genetic control among the evaluated traits. Plant height consistently exhibited high heritability across all growth stages (Table 5), indicating that most of the observed phenotypic variation in this trait is genetically determined. High heritability suggests that selection based on plant height could be effective even during early developmental stages. Similar findings were reported by Kumar et al. (2026) and Singh et al. (2023), where traits with high heritability coupled with high genetic advance were considered reliable indicators of additive gene action and selection efficiency. Leaf area exhibited moderate to high heritability, indicating that both genetic and environmental factors influence its expression. Moderate heritability for vegetative traits is common in perennial crops where environmental conditions interact with genotype to determine growth performance. Previous studies have reported moderate to high heritability for several growth and yield traits in oil palm, reinforcing their usefulness as selection criteria in breeding programs (Latif et al., 2021; Zulkifli et al., 2023; Singh et al., 2020).


 
Genetic advance and prospects for selection
 
Genetic advance expressed as percentage of mean (GAM) provides insight into the expected response to selection. In the present study, plant height and leaf area consistently exhibited relatively high GAM values across growth stages, suggesting that these traits are largely governed by additive gene effects. At 8.5 MAT, biomass-related traits including shoot biomass, root biomass, basal biomass and total biomass displayed high GAM values coupled with moderate to high heritability (Table 5). The combination of these parameters indicates that these traits can respond effectively to phenotypic selection. High genetic advance together with moderate or high heritability is widely considered indicative of additive gene effects and favorable conditions for genetic improvement (Arolu et al., 2019; Latif et al., 2021). These findings are consistent with earlier research demonstrating that vegetative vigor and biomass accumulation often exhibit strong genetic control and respond well to selection in oil palm breeding programs (Murphy, 2019; Rival and Jaligot, 2020).
 
Trait associations and biomass accumulation
 
Correlation analysis further revealed significant relationships among several vegetative and biomass traits (Fig 1). Plant height showed strong positive correlations with shoot biomass, root biomass and total biomass, indicating that taller seedlings tend to accumulate greater biomass. These results suggest that plant height is an important indicator of seedling vigor and productivity potential. Basal circumference also exhibited strong positive correlations with biomass traits, particularly shoot biomass and total biomass. Similar relationships between stem girth and biomass production have been reported in oil palm and other perennial crops (Corley and Tinker, 2016; Woittiez et al., 2017).


       
Leaf area was positively correlated with plant height and basal circumference, confirming the importance of canopy expansion in supporting vegetative growth. Previous studies have highlighted the role of canopy traits in determining growth performance and yield potential in oil palm (Murphy, 2019; Rival and Jaligot, 2020).

The study highlights strong genetic variability among the eleven oil palm genotypes tested at the nursery stage. Key growth traits such as plant height, leaf area and basal circumference showed moderate to high heritability and genetic advance, indicating they are largely controlled by additive gene effects and can be improved through selection. Growth traits increased steadily from 3 to 8.5 months after transplanting, confirming the value of early-stage evaluation for identifying vigorous seedlings. Genotypes G1, G7 and G3 consistently outperformed others, making them promising candidates for breeding programs.

The present study was supported by Ghana Sumatra Limited.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.

The authors declare that there are no conflicts of interest regarding the publication of this article. No funding or sponsorship influenced the design of the study, data collection, analysis, decision to publish, or preparation of the manuscript.