Kenaf (Hibiscus Cannabinus L.): A Promising Fiber Crop with Potential for Genetic Improvement Utilizing Both Conventional and Molecular Approaches

ABSTRACT Kenaf is a fiber crop belonging to the genus Hibiscus (Malvaceae), and the potential of this plant, its multipurpose use, and its environmentally friendly cellulose have placed kenaf at the forefront of both commercial and subsistence farming. Due to inadequate agricultural practices, low production potential, and photoperiodism, the yields of fiber are relatively low. The varietal development in kenaf is hindered by a lack of knowledge of its heredity, which also affects its successful usage and protection of important germplasm. The amount and production potential of kenaf are enhanced by identifying and exploring obtainable genetic resources for the development of high-yield cultivars. Knowledge of existing natural genetic variation and its availability is important for this highly valued crop’s genetic improvement. This review summarized recent advances in kenaf varietal improvement using marker-assisted breeding, genetic linkage maps, and morphological and molecular assessment of genetic diversity. Existing issues were discussed to produce scientific references for identifying photo-insensitive kenaf genotypes.


Introduction
Kenaf (Hibiscus cannabinus L.) is an industrial crop belonging to the Malvaceae family and it is mostly cultivated for its exceptional air permeability, antibacterial properties, and excellent qualities such as salinity tolerance, drought resistance, wide adaptability, and high fiber yield. Global responsiveness to "save the environment" increased the global demand for Jute and Allied Fiber (JAF) since natural 16II + 4I. Kenaf has approximately 120 names, including mesta, roselle, treal, ambary hemp, and rama (Sellers 1999), reflecting the fibrous species' diversification and widespread use. Cheng et al. (2004) used AFLP fingerprinting to show that kenaf and roselle are two distinct but related species.

Flowering and photoperiodism
The kenaf plant continues to be in its vegetative phase and is characterized as a photoperiod-sensitive crop when the length of the day is shorter than 12 hours or 12 hours and 45 minutes, according to Carberry et al. (1992) and Alexopoulou et al. (2013), respectively. Kenaf can grow in areas with a relative humidity ratio of 68 to 82% and temperatures varying from 22.6 to 30.3°C (Coetzee 2004). As reported by Bukenya-Ziraba (2004), planting season influences flowering; vegetative growth is slowed by long days and warm temperatures. Following an assessment of variance for different yieldcontributing components, Shao et al. (1993) found highly significant results in jute (C. capsularis L.) and kenaf (H. cannabinus L.). Bhattacharjee et al. (1987) reported that H. cannabinus whole plants harvested at 90-110 DAS were suitable for making standard newsprint. Studies show a strong correlation between the first flower node and effective plant height; the higher the first flower node, the more fiber is produced in kenaf (Li et al. 2016). The integrated Specific-locus amplified fragment sequencing (SLAF-seq) along with bulked segregant analysis (BSA) can identify a single-nucleotide polymorphism locus (S961-2) that is strongly associated with the first flower node feature of kenaf (Li, Li, and Zhao 2019).
The flowering of kenaf can be influenced by environmental conditions that exist during the cropping season. Taller plants usually bloom earlier and from an agronomic perspective, the negative association between plant height and flowering time is a valuable criterion since taller plants produce better fiber yields and allow for an earlier harvest. This allows for early and adequate land preparation in readiness for the next cropping season (Basu and Chakravarty 1971). Plants sown in March and June are exposed to long days, high temperatures, high humidity, and high rainfall, and these lead to good vegetative growth. On identical days, the kenaf flowers usually close at noon. According to Bukenya-Ziraba (2004), kenaf is primarily an outbreeding plant with up to 30% self-pollination. Although kenaf is primarily self-fertile, it is frequently stated as a cross-pollinated crop because pollination is usually carried out by pollinating agents such as honeybees or insects (Singh 2010). Early flowering cultivars are ideal for feeds, whereas late flowering and leafy varieties are suitable for fiber and seed production (Raji 2007). In most kenaf, fiber growth quickly declines after flowering (Li, Li, and Zhao 2019). Six highly inbred photosensitive kenaf cultivars were crossed, and a major additive impact was identified for days to flowering character, suggesting the possibility of effective selection for earliness in these cultivars (Gray et al. 2006). The influence of photoperiod and daily light on flowering in five different Hibiscus species was explored by Warner and Erwin (2003). Kenaf plants with effective photosynthetic activity can generate a lot of biomasses (Hossain et al. 2012). Sowing dates set the vegetative phase for kenaf whereas early sowing prolongs the vegetative phase, allowing the crop to succeed in critical photoperiodic levels. Delayed flowering and photoperiodism have been recognized as the most important traits for growing kenaf plants in tropical countries such as Malaysia (Hossain et al. 2011). However, in the absence of diverse traits in the gene pool, mutagenesis is often used in crops to create valuable traits such as plant height, days to flowering, color variation, and pathogen tolerance (Kang et al. 2016;Oladosu et al. 2016).

Kenaf importance: Benefits, prospects and economic potential
Kenaf is considered a jute substitute and has received great attention due to its status as a multipurpose fiber crop. New methods of utilization have seen kenaf usage in animal feed, filtration media, board making, potting media, oil absorption, pulping, paper making, car interiors, building boards and even athletic wheelchairs (Lips et al. 2009). Kenaf can be used for a variety of purposes including paper, pulp, animal bedding, construction materials, and carpet backing (Li et al. 2016;Zhao et al. 2013). It is presently cultivated for multiple uses such as thermal insulation boards, pulp, energy sources and building materials (Li et al. 2016). Kenaf is used as raw material and as an alternative to wood in pulp and paper industries to avoid deforestation (Khalil et al. 2010). Chemically modified kenaf fiber can also be used as a sorbent material for wastewater purification, smart textiles, electrostatic discharge protection, and composite reinforcement (Mohammed et al. 2017;Tharazi et al. 2017).
Kenaf is a highly adaptable plant that adjusts well to various soil types and climates to grow its fiber and seed oil (Liu and Labuschagne 2009). Due to its vast adaptability to all types of soils, kenaf has the potential to be grown on marginal soils usually characterized by low productivity, low water-holding capacity, and low nutrient availability (Roslan et al. 2010). Kenaf consists of various beneficial components like stalks, seeds, leaves, fibers, oils, proteins, allelopathic chemicals, and fiber strands, among other things (Akinrotimi and Okocha 2018). Although the plant is cultivated for its fiber, its leaves and seeds are used to treat various illnesses in India and Africa (Ayadi et al. 2017). Improved αcellulose gratification, especially in kenaf bast, has been proven to strengthen kenaf-based products (Edeerozey et al. 2007). The bast fiber is by weight made up of 8-15% lignin, 56-60% cellulose, and 21-35% hemicellulose . Kenaf fibers are among the most important for bast fibers, which produce a high-quality pulp suitable for industrial and textile uses (for carpets, canvases, sacs, cordages, ropes, etc.) (Hamidon et al. 2019). On the other hand, the bast fibers remain the most important source of income for kenaf farmers, finding important uses in new products such as nonwoven fabrics and reinforced composite materials used in automotive, packaging, aerospace, and other industrial applications (Sen and Reddy 2011). The bast fiber has a higher α-cellulose (55%) content compared to the core fiber (49%) ( Table 1).
Furthermore, the core (inner part) with high hemicellulose and cellulose is used as an adsorbent in animal bedding and bioethanol production (Cosentino et al. 2008;Patanè and Sortino 2010). Khalil et al. (2010) reported that kenaf core fibers had higher holocellulose and lignin content than kenaf bast fibers. However, kenaf bast fibers had higher cellulose, extractive, and ash content than both of kenaf fibers. Different parts of kenaf and allied fiber crops in various forms could also be used directly to treat several human diseases and its use as herbal medicine to regulate or prevent dysentery, worms, and constipation has been reported (Karmakar et al. 2008).
Many researchers have investigated kenaf as a low-cost, recyclable, renewable, and biodegradable alternative to synthetic polymers (Ahmad et al. 2011). According to Ryu et al. (2017a), kenaf leaves are used as vegetables due to their high antioxidant and phenolic content. Hence, the leaves are a delicacy and are used as ingredients for sausages in the southern part of India and Africa (Bukenya-Ziraba 2004). Kenaf leaves and petioles contain 15 to 30% crude proteins with high digestibility (Table 2). Monti (2013) described that kenaf seeds could also be used as medication for various health complications and diseases, such as cholesterol poise, some forms of cancers, and blood pressure. According to Wong et al. (2014), kenaf seed oil and kenaf seed extraction may well be a possible source of common anti-cancer agents. In addition, according to Ho, Ang, and Lee (2008), kenaf could be a potentially suitable species for phytoremediation within the ecliptic, with the common goal of biomass production, especially to recover the biological and financial value of degraded areas. Furthermore, kenaf plants have the flexibility to absorb phosphorus and nitrogen from the soil due to their ability to accumulate carbon dioxide emissions at a high rate ). More research into the utilization of kenaf seeds for antiproliferative properties is required. The analysis of kenaf oil was conducted by Mohamed et al. (1995) and the result is shown in Table 3. Phosphatidyl choline, phosphatidyl ethanolamine, and phosphatidyl glycerol were discovered to be the prevalent phospholipids during this study.
The ASEAN Free Trade Agreement (AFTA) has prompted the National Economic Action Council (NEAC) of Malaysia to resolve to employ kenaf as a replacement for tobacco to provide a significant natural raw fiber for use in the textile, construction, automotive, paper-making and other technological industries (Anuar and Zuraida 2011;Srayya and Kumar 2015). According to Saba et al. (2016), the Malaysian government has recognized the kenaf plant as Malaysia's seventh commodity plant.

Genetic diversity in kenaf based on morphological features
Classical genetic study (generation means analysis) revealed essential information that leads to a better understanding of the genetic makeup of important agronomic traits of kenaf and selection in the segregating generations would significantly improve fiber yield (Behmaram et al. 2014). Chromosomal diversity, which is reflected in high levels of morphological and physiological variability, is a rich source of material that can help kenaf breeders improve the crop (Wilson and Menzel 2003). According to Echekwu and Showemimo (2004), most of the traits should lead to genetic improvement in plant height, number of seeds per pod, 1000 seed weight, and seed yield. Ibrahim et al. (2013) assessed the genetic variability and heritability of thirteen different plant characters in sixteen germplasm of Roselle (H. sabdariffa L.) grown in Shambat (Sudan) over two seasons.  (Khalil et al. 2010 According to Bahtoee, Zargari, and Baniani (2012), kenaf fiber yield increased by 148.45% due to increase plant height and stem diameter. The genetic diversity of 84 kenaf accessions from 26 countries and regions was investigated by Zhang et al. (2013), while Heliyanto, Hossain, and Basak (1998) investigated the genetic variability of kenaf germplasm and discovered significant genetic variability for plant height, base diameter, node number, fiber, stick weight, days to flowering, and fiber production. Other physiological processes and environmental conditions can also impact plant development and biomass output, even though photosynthesis acts as the primary mechanism for growth and accounts for around 90% of the dry mass in crops (Hossain et al. 2012). Mostofa et al. (2002) studied the genetic diversity, heritability for fiber yield, and other yieldcontributing features of 33 kenaf genotypes from varied origins. Similarly, Hossain et al. (2012) worked with forty kenaf accessions and both researchers concluded that the traits with high heritability and genetic advance may well be efficiently upgraded through deliberate improvement efforts. Wong et al. (2008) suggested that late-flowering accessions are resistant to phytophthora and leaf hopper damages. Cheng et al. (2002) reported that kenaf genotypes established on morpho-agronomic features for heritable diversity had strong genetic advancements with high heritability for green weight per plant and days to 50% flowering.
Recitation of genetic diversity on morphophysiological traits is comparatively easy to match to others (Benor et al. 2012). However, the environment greatly influences morphological evaluation, and the method is associated with a low polymorphism rate, higher risk of bias, large plant population assessment, and high cost of labor (Sarif et al. 2020). Despite the limitations of morphological assessment in quantifying genetic diversity, the method provides sufficient information for crop characterization (Mat Sulaiman et al. 2020). The wide variation in the crop botanical and agro morphological properties suggests that the genotypes are genetically diverse (Ogunniyan 2016). According to Faruq et al. (2013), there is significant differentiation among 32 kenaf accessions, and high-yielding late mature genotypes can be crossed with intermediate flowering genotypes to produce a photo-insensitive variety with improved fiber and stick yield for hot climates such as Malaysia Variance components can be used to quantify the strength of a genetic influence on a trait, associate genes responsible for influencing specific traits, investigate possible shared influences in related traits through multivariate analysis and quantify the genetic strength in expressing a trait by analyzing genegene and gene-environment interaction (Almasy and Blangero 2010). Phenotypic coefficient of variation (PCV), the total variation influencing an observed phenotype, Genotypic coefficient of variation (GCV) and the quantum of phenotypic variation influenced solely by genetic factors, are generally used in the replacement of phenotypic and genotypic variance as its expression in ratio to the mean enable the comparison of values obtained by different traits (Falconer 1960). In breeding, a higher GCV is preferred, indicating the strength of a plant's genetics in expressing the phenotypic trait. The range between the PCV and GCV is usually attributed to other influences which may affect the observed phenotype. This usually comes from an array of factors such as climate, soil, nutrients, and management which are generally categorized as environmental influences in most cases (Monnahan, Kelly, and Carlborg 2015). As such, a wider range between PCV and GCV would indicate a stronger environmental effect in the expression of a specific trait and selections based on that trait may not be effective for further improvement (Tuhina-Khatun et al. 2015). A large variation (Figure 2) was observed among the 28 kenaf mutants, indicating a large variation in leaf color and shape, flower color, and pod shape characteristics (Al-Mamun et al. 2020). (Insert Figure 2)

Molecular diversity assessment of in kenaf
Molecular breeding or marker-assisted breeding refers to the technique of using DNA markers that are linked to phenotypic traits to assist in the selection of target traits in the breeding program (Jaradat 2016). Molecular markers are simple to characterize and do not require waiting until a plant has completed its growth cycle because samples could be taken from any plantlet. Identifying kenaf cultivars simply based on morphological and agronomical traits might be difficult (Deng et al. 1991;Deng, Li, and Li 1994), as a result, molecular markers are preferred to morphological markers (Datta et al. 2021). Understanding the kenaf germplasm genetics and breeding of elite varieties necessitates studying the plant's genetic diversity, which has been done to some extent (Su 2002;Su et al. 2003). By Blast searching against the reference genome using the sequences of surrounding molecular markers linked to QTLs, 374 potential genes, including cellulose synthase-like genes, MYB genes, and Agamous-like genes, were found in these loci in kenaf (Xu et al. 2022).
At present, several molecular markers such as Simple sequence repeats (SSRs), Inter simple sequence repeat (ISSR), Amplified fragment length polymorphism (AFLP), Random Amplified Polymorphic DNA (RAPD), Restriction fragment length polymorphism (RFLP), etc. are proven to be beneficial tools for studying genetic diversity, marker-assisted breeding, and germplasm collections (Banerjee et al. 2012). Breeders can determine agronomic traits of interest and track the trait in genetic crosses. However, plant genomes typically contain large quantities of respective DNA that are not publicly available and do not contribute to the morphological or physiological availability of the plants. Few morphological distinctions do not convey true genetic dissimilarity at the dust level within the event of nearly all plant varieties and species. As a result, polymorphism in DNA, which may provide information about genetic diversity, is currently being investigated. The literature published elsewhere within the world associated with the present research is given here.
Molecular markers including AFLP, ISSR, and RAPD have been used to investigate kenaf germplasm's genetic diversity and evolutionary linkages (Tao et al. 2005). Zhang et al. (2011) used 134 marker sites to generate a high-density kenaf genetic linkage map (including 56 ISSR, 13 RAPD and 65 SRAP markers). Lutfur Rahman et al. (2007) used RAPD, SSR, and AFLP markers to identify kenaf, mesta, and jute varieties, and stated that molecular mapping of desirable genetic features will likely strengthen plant breeders' hands in developing new elite cultivars. Chen et al. (2011) constructed a genetic linkage map for kenaf using SRAP, ISSR, and RAPD markers. Guang, Defang, and Anguo (2009) studied the genetic diversity using ninety-one ISSR molecular markers suggesting that genetic relationships among kenaf cultivars are relatively close, and their genetic similarities narrow. Molecular mapping of desirable genetic traits is likely to strengthen the plant breeders to develop newer elite cultivars (Lutfur Rahman et al. 2007). The identification of the gene encoding the homeobox transcription factor LATE MERISTEM IDENTITY 1 (HcLMI1) that controls lobed leaf is made possible by gene mapping (Zhang et al. 2020).

Simple sequence repeat (SSR) marker
Microsatellites have become the preferred molecular marker for a variety of reasons. These microsatellites, which include repetitive and unique sequences, are found in both animal and plant genomes. Microsatellites or SSR are among the furthermost familiar genetic markers due to their abundance, codominance, reproducibility, and high genome coverage (El-Esawi et al. 2016). SSRs have proven to be a strong and popular method of obtaining useful and high polymorphism levels for various plant germplasm. SSR markers are the most effective markers for studying genetic variation in many plants, according to Rakoczy-Trojanowska and Bolibok (2004).
SSRs are widely utilized in molecular breeding studies and genetic mapping in plants due to their locus reliability, co-dominant inheritance, specificity, and significant polymorphism (Li et al. 2016). Due to their high allelic diversity and codominance, SSR showed a high ability to assess diversity levels, genetic structure, and relationships (Ismail et al. 2019). Zhou et al. (2015) and Nawaz et al. (2017) used these markers to assess genetic diversity during a different cultivar of several plant species. SSRs are divided into two types supporting their source: genomic SSRs (gSSRs) and expressed sequence tag SSRs (EST-SSRs). Genomic SSRs are usually associated with non-coding parts, but EST-SSRs are derived from the genome-expressed parts (Li et al. 2004). EST-SSRs are found in the genome's transcribed region and may be relatively well conserved. As a result, any polymorphism discovered using EST-SSRs could indicate a greater connection between species. Evaluation of germplasm with SSRs derived from ESTs may improve the usefulness of genetic markers by assaying changes in transcribed and known-function genes (Eujayl et al. 2002).

Expressed sequence tag SSRs (EST-SSR) marker
Kenaf's expressed sequence tags (EST) database and transcriptome database (SRP060459) were evaluated to find the potential homologs (Zhang et al. 2015). Within the 32 kenaf cultivars, Ryu et al. (2017b) identified 225 polymorphic loci using 80 SSR primer sets. Li et al. (2016) raised largescale SSR markers for kenaf and exploration of fiber growth and improvement in kenaf and genomics studies. EST-SSR and coding SSR are closely related to functional genes that may control some important genetic characteristics (Li et al. 2016). They identified 9324 supplementary pairs as nominal EST-SSR markers, and 61 primer pairs were polymorphic between 28 kenaf accessions. They suggested that new resources will afford the creation of genetic linkage maps, investigation of fiber growth and expansion in kenaf, aside from its importance to new gene detection and applied genomic studies. A genetic diversity analysis of 45 accessions in kenaf using 70 newly established EST-SSR markers previously divided them into three groups based on their blooming time (Jeong et al. 2017).

Inter-simple sequence repeats (ISSR) marker
The inter-simple sequence repeat (ISSR) method fortifies inter-microsatellite arrangements at various loci throughout the genome ). The ISSR marker was amplified with one primer supporting the SSR motif and anchored at the 50 or 30 ends of the 2-4 degenerate nucleotide sequence (Li et al. 2016). Tao et al. (2005) concluded that ISSR markers can be used to condition the genetic associations between kenaf varieties. Satya et al. (2013) reported that 13 ISSR markers showing high polymorphism and best reproducibility were selected for counting and further analysis of 19 ISSR markers. Xu et al. (2013) identified 90 ISSR primers with polymorphisms, each of which produced a minimum of 1 distinct and well-set polymorphic broadened band. The genetic differences of 84 kenaf samples from 26 countries and regions were investigated using 28 ISSR primers and 193 polymorphism bands . Guang, Defang, and Anguo (2009) mentioned two different male-purified kenaf varieties, two gene pools emerged and combined to make a primer that may distinguish between fertile and sterile genes.
The genetic diversity and genetic relationship of some kenaf genotypes using ninety-one ISSR molecular markers for amplification on 44 shares of kenaf germplasm resources, of which 21 showed good diversity reported by Guang, Defang, and Anguo (2009). The later developed a primer that can display the variation of two male sterilized kenaf varieties' fertile and sterile gene pools. Lin et al. (2008) investigated the genetic diversity and the relevance of kenaf germplasm from 32 kenaf accessions from 20 countries using 22 ISSR primers. The cluster analysis outcome reported that almost all cultivars had low genetic relationships and low genetic diversity.

Amplified fragment length polymorphism (AFLP) marker
The AFLP DNA fingerprinting technique using selective PCR amplification of restriction fragments within a complete restriction digest of genomic DNA (Vos et al. 1995), has advantages in terms of reproducibility, detection of high-level DNA polymorphism, genome distribution throughout the marker, and also the need for prior sequence information of the studied genome (Prabhu and Gresshoff 1994). Kim et al. (2010) investigated the genetic diversity of 17 kenaf varieties grown in Korea using morphological characters and also the AFLP technique. Coetzee, Labuschagne, and Hugo (2008) studied genetic diversity and fixed genetic associations in 19 kenaf genotypes and three wild types for AFLP analysis. AFLP-based marking off and genetic relations of kenaf germplasm were conducted by Cheng et al. (2004). Within a study of 25 germplasms using AFLP markers, Qiang et al. (2003) observed the existence of a powerful relationship between Hibiscus sabdariffa and Hibiscus radiation. In other research, Cheng et al. (2004) worked on 23 kenaf accessions and a couple of roselle (H. sabdariffa var altissima) accessions and found that recognizing kenaf accession created solely on morphological characters is difficult because of their narrow distinction. They concluded that molecular techniques like AFLP fingerprinting were useful in identifying genetic diversity between the kenaf accessions with different origins.

Random amplified polymorphic DNA (RAPD) marker
Random amplified polymorphic DNA (RAPD) technology provides a strong tool for recording genetic differences in organisms (Welsh and McClelland 1990;Williams et al. 1990). When employed in conjunction with morpho agronomic character analysis, the RAPD markers system may be a powerful tool for identifying kenaf varieties and determining their genetic relationships (Cheng et al. 2002). Due to its advantage in rapidly assessing the genetic composition of several individuals, RAPD is widely used for plant diversity analysis (Bhattacharya and Ranade 2001). Furthermore, it is often used at any stage of plant development where other methods, like isozyme analysis, have proven ineffective (Sreekumar and Renuka 2006).
RAPD can be one primer-based marker that detects multiple variable loci within the chromosome (Faruq et al. 2015). This expertise is easy to use and profitable; it only requires one RAPD primer but allows for detecting differences at multiple loci. Faruq et al. (2015) identified 36 polymorphic loci in 25 kenaf cultivars exposed to high genetic polymorphisms of the markers using five RAPD primer sets. Lutfur Rahman et al. (2007) studied kenaf, mesta and jute varieties for morphology and molecular traits. Cheng et al. (2002) reported that the genetic association of kenaf varieties obtained from morpho-agronomic characterization was difficult to differentiate individual kenaf varieties, however, RAPD analysis was found useful for this purpose. There are 192 bands in total, 149 polymorphic and 43 monomorphic. RAPD markers were used to assess the genetic relationships of twenty-five accessions from seven species, revealing an exhaustive relationship between Hibiscus radiatus and Hibiscus cannabinus (Anping, Peng, and Jianguang 2002). Li and Quiros (2001) created the sequence-related amplified polymorphism (SRAP) technique widely used in Europe, United States and China. It has a moderate throughput ratio and enables simple band sequencing. To assess genetic diversity, phylogenetic relationships, and evaluate germplasm, Qi et al. (2011) used the SRAP molecular marker to identify 84 different kenaf varieties collected from 26 different countries and regions around the globe. The 84 kenaf varieties were divided into three groups by SRAP cluster analysis: cultivar, semi-wild, and wild types, revealing the genetic evolution of kenaf. Zhang et al. (2011) created a genetic linkage map of kenaf using an assemblage of superior consistency molecular markers consisting of thirteen RAPD, fifty-six ISSR, and sixty-five SRAP markers. When evaluating parental lines, SRAP primers confirmed lesser polymorphism than RAPD and ISSR primers but fashioned clearer bands that were too simple be to recognize by the other primers. As a result, it may be useful in the creation of kenaf maps. Tao et al. (2005) found that SRAP could be a cost-effective and dependable molecular marker after studying genetic diversity and phylogenetic association in 30 kenaf varieties.

Improvement of kenaf for fiber yield
Kenaf fiber yield is a complex trait prompted by morphological and physiological factors. Several factors, like genotype, season length, sowing date, plant population, photosynthesis, and crop maturity, influence kenaf component yields (Paridah, Abdelrhman, and Shahwahid 2017). Jianmin et al. (2005) showed that plant height, fresh bark thickness, dry bark weight per plant and fiber fineness of kenaf were regulated by additive and dominance gene actions. These findings were supported by Voulgaridis and Grigoriou (2000), who found that both the genetics of the tree and external elements like light, water, and nutrients can impact fiber length. Six QTLs were identified from which QPH, QFBW, QDBW, and QFW were associated with fiber yield, while QFT and QFC were related to fiber quality that were assigned to three linkage groups, namely LG16, LG8, and LG3 (Hui et al. 2021). Candidate genes involved in the production of cell walls have been found using quantitative trait loci (QTL) for fiber yield and quality-related factors (Zhang et al. 2020). Genetic inheritance and manipulation, environmental conditions, management practices, and agricultural inputs all influence fiber form and quality (Hossain et al. 2011). Heterosis for fiber yield is well-known, and kenaf hybrid cultivars have been generated and used commercially in China (Liu 2005). Several researches have been conducted on heterosis research kenaf hybrids. Liu (2005) also mentioned that high heterosis for yield characteristics favored the mid-parent and better parent.
In an extremely diallel analysis of kenaf, a substantially additive effect was also shown for days to flowering (Gray et al. 2006). Hybrid kenaf has received much attention due to its enhanced fiber quality and resistance to force (Aifen, Jianmin, and Peiqing 2008). According to Li, Chen, and Gong (2000), hybrid kenaf cultivars are commonly planted in China and are gaining popularity in India. The major cytoplasmic male sterile line in kenaf was created from wild UG93 and then employed as a universal strategy for creating F 1 hybrid seeds, according to Zhou (2002). The general procedure for kenaf cultivation is presented in Figure 3. (Insert Figure 3)

Future outlook
Kenaf is an important industrial crop and a renewable source for the bio-composite sector, however, there is a scarcity of genetic information on the plant, preventing commercialization. Farmers should follow the scientific procedure of kenaf cultivation to expand local and international markets for kenaf fiber and commodities. The government must be involved and insured in order for the crop to provide a market condition that encourages farmers to plant this commodity. The farmers must also execute an excellent kenaf cultivation method to ensure a constant supply of high-quality kenaf fibers to meet the rising emergence of kenaf biocomposites. Kenaf is currently processed using traditional retting methods and this retting process has a bearing on the fiber's properties. Kenaf is tolerant to drought (Banuelos, Bryla, and Cook 2002) and has a moderate tolerance to salinity (Jin, Sun, and Cho 2012). The goal of kenaf breeding in the near future is to enhance salt resistance, insect resistance, drought-tolerant transgenic breeding, and herbicide resistance. Additionally, kenaf breeding should help to create a molecular marker heritable linkage map, clone a kenaf functional gene, and locate QTLs for a few of the plant's most significant monetary qualities. The receptor kenaf variety Fuhong 952 was used by Qi, Xu, and Lin (2008) to increase the expression of target genes associated with Bt insect resistance. Through the pollen tube pathway, Cao and Li (2000) incorporated bar genes with exogenous herbicide resistance into kenaf. The salt-resistance gene SaNHX of Spartina anglica was transferred into kenaf plants by Wu et al. (2010) using the pollen tube pathway. Bright kenaf fiber sells at a higher market price than existing ones, so emphasis may be placed on ongoing research plans and commercial policies to develop a new cultivar of bright fiber. Kenaf cultivation should be done based on modern scientific methods to fulfill the demand for the world market, and a range of recent and different kenaf products should be produced.

Conclusions
A modern genetic map of kenaf is important in continuing efforts to hereditarily differentiate kenaf germplasm collections and advance core collections that may be exploited by outdated breeding programs, as described in this manuscript. It is noteworthy that there is a dearth of research into the development of kenaf fiber production despite its enormous potential. With partial inputs, a well-planned labor program with precise targets from all angles should be formed on kenaf, which is suitable under extremely limiting soil moisture conditions. Kenaf may formerly be "all over the place," but more research and concessions are required for ASEAN countries to take advantage of this miracle plant's financial and environmental benefits. More suggestive molecular data must be accumulated to control the range and genetic associations of kenaf germplasm worldwide for its efficient utilization. For worthwhile farming of kenaf, selecting the right genotype with high increase rates and biomass production could be very important. Modern biotechnological approaches and apparatuses alongside traditional methods through marker-assisted selection have the likelihood to attain product-specific improvement in kenaf.

Highlights
• This manuscript will provide listing on recent kenaf varietal improvement research on use morphological and molecular genetic diversity assessment. • The genetic improvement of this highly valued crop and knowledge of existing natural genetic variation has been cited. • Data were provided on tropical climates, photoperiod-intolerant cultivars, and late-flowering Kenaf cultivars. • These findings could be applied to future conservation breeding programs and genotype identification.