International Journal of Horticulture, 2025, Vol.15, No.4, 171-184 http://hortherbpublisher.com/index.php/ijh 173 terpenes in the flowers drops significantly, greatly reducing the medicinal value of pollinated flowers (Feder et al., 2021). Therefore, in commercial cultivation, male plants are typically removed to prevent pollination and ensure the production of seedless, high-THC female flowers, known as sinsemilla. 3 Genetic Diversity and Classification 3.1 Genetic variability within species Recent advancements in genomics have significantly enhanced our understanding of the genetic diversity within Cannabis species. Simple sequence repeat (SSR) markers have been developed and utilized to assess genetic variation and population structure in Cannabis sativa. For instance, a study identified 92 409 SSR motifs and developed 63 707 complementary SSR primer pairs, which were used to estimate genetic diversity and population structure, revealing substantial polymorphism and genetic diversity within the species (Zhang et al., 2020). Whole-genome shotgun sequencing has been employed to explore gene copy number variations (CNVs) that influence cannabinoid synthesis and pathogen resistance, providing insights into the genetic mechanisms underlying these traits (McKernan et al., 2020). Reduced representation shotgun sequencing has also been used to identify single nucleotide polymorphisms (SNPs) that can diagnostically classify Cannabis varieties, further elucidating the genetic structure of the species (Oultram et al., 2022). Genetic variability is crucial for the breeding and selection of desirable traits in Cannabis. High genetic and phenotypic variability within and among hemp cultivars has been observed, which is beneficial for breeding programs aimed at improving agronomic traits such as flowering time, plant height, and biomass (Trubanová et al., 2023). This variability allows breeders to select for specific traits, enhancing the potential for developing new cultivars with desired characteristics. For example, the identification of genetic markers associated with key traits through genome-wide association studies (GWAS) has provided valuable tools for marker-assisted selection, facilitating the breeding of Cannabis varieties tailored for specific medicinal or industrial purposes (Ronne et al., 2023). 3.2 Taxonomic controversies and challenges The taxonomic classification of Cannabis has been a subject of ongoing debate, particularly regarding the distinction between the sativa, indica, and ruderalis varieties. Traditional classifications based on morphological traits have been challenged by molecular evidence. For instance, DNA barcoding has been used to examine the taxonomic classification of Cannabis, with findings supporting a unique species system (C. sativa) comprising two subspecies: C. sativa subsp. sativa and C. sativa subsp. indica (Barcaccia et al., 2020). This molecular perspective suggests that the traditional classification into distinct species may not be as clear-cut as previously thought. Molecular and genetic studies have provided evidence both supporting and refuting traditional classifications of Cannabis. For example, population structure analysis using SSR markers has identified distinct genetic groups within Cannabis, which may correspond to traditional classifications based on geographical origins and sexual behaviors (dioecious and monoecious) (Borin et al., 2021). However, other studies have shown that genetic diversity within Cannabis does not always align with traditional morphological classifications, indicating that a more nuanced understanding of the species' genetic structure is needed (Kovalchuk et al., 2020). These findings highlight the complexity of Cannabis taxonomy and the need for further research to reconcile molecular and traditional classifications. 3.3 Cultivar development and breeding Hybridization has played a significant role in the development of commercial Cannabis strains. A study pointed out that a key issue to address in the breeding process of new Cannabis varieties is the taxonomic uncertainty between the two major groups of the Cannabis genus, namely Indica and Sativa. Using DNA barcoding technology, the research provided molecular support for a single species system of Cannabis sativaand proposed that constructing F1 hybrids through molecular breeding programs holds great potential (Barcaccia et al., 2020). The results showed that controlled breeding programs to create F1 hybrids, combining desirable traits from
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