Medicinal Plant Research 2024, Vol.14, No.4, 196-209 http://hortherbpublisher.com/index.php/mpr 205 7 Genetic Studies and Breeding 7.1 Genetic diversity and germplasm The genetic diversity and germplasm of loquat (Eriobotrya japonica) have been extensively studied to understand the evolutionary history and domestication processes of this fruit. A high-quality chromosome-level genome assembly of wild loquat has revealed significant genetic resources that are crucial for breeding improved varieties. Comparative genomics analysis indicates that loquat shares a common ancestor with apple and pear, and a recent whole-genome duplication event occurred before its divergence. The genome resequencing of loquat germplasms has shown distinct classifications between wild and cultivated groups, with commercial cultivars experiencing allelic admixture. Wild loquats exhibit higher genetic diversity and fewer selected genomic regions compared to cultivated loquats, which have undergone selective sweeps related to fruit quality, size, and flesh color during domestication (Jing et al., 2022). 7.2 Breeding for bioactive compounds Breeding efforts in loquat have focused on enhancing bioactive compounds, which are essential for the fruit's nutritional and pharmacological properties. For instance, the dynamic changes in organic acid (OA) content during fruit development and ripening have been studied in common loquat and its interspecific hybrid. The predominant OA compound, malic acid, along with other acids like succinic and tartaric acid, are regulated by key enzymes such as PEPC and NAD-MDH. These findings provide a fundamental basis for future breeding programs aimed at improving loquat's nutritional quality (Deng et al., 2023). Additionally, Wang et al. (2021) developed a qPCR system for detecting the genotype of polyploid loquat, particularly focusing on the genotype related to flesh color. This method, by analyzing the DNA ratios of different genotypes, enables accurate identification of tetraploid and triploid loquat genotypes, providing a powerful tool for selecting superior breeding lines. In another study, Wen et al. (2020) developed a detection method combining simple sequence repeat (SSR) markers with qPCR, known as SSR-qPCR, for detecting the aneuploid molecular karyotype of loquat. This method effectively identifies and constructs the molecular karyotype of aneuploid individuals, offering a new tool for genetic research in polyploid plants. 7.3 Future directions in genetic research Future genetic research in loquat should focus on several key areas to further enhance the understanding and improvement of this fruit. One promising direction is the exploration of the molecular mechanisms underlying heterosis in triploid loquats. Studies have shown that triploid loquats exhibit greater growth vigor compared to diploids and tetraploids, potentially due to altered circadian rhythms. The expression levels of circadian clock genes and their output genes in triploid loquats have been found to be higher than in their parental types, suggesting a link between circadian rhythms and heterosis (Liu et al., 2019). Another important area is the identification and functional analysis of genes involved in the biosynthesis of bioactive compounds. For example, the transcriptional activator EjMYB4 has been identified as a key regulator of lignin biosynthesis in loquat, providing insights into the genetic control of this important structural compound (Zhang et al., 2018). Continued research in these areas will be essential for developing new loquat varieties with enhanced nutritional and pharmacological properties. 8 Challenges and Future Perspectives 8.1 Research gaps Despite the promising pharmacological activities of bioactive compounds in loquat, several research gaps remain. One significant gap is the limited understanding of the specific mechanisms through which these compounds exert their effects. While studies have demonstrated the anti-tumor, antibacterial, anti-inflammatory, and antioxidant activities of loquat extracts, the precise molecular pathways involved are not fully elucidated (Silva et al., 2020; Xiao et al., 2023). Additionally, there is a lack of comprehensive clinical trials to validate the efficacy and safety of these bioactive compounds in human populations. Most of the current evidence is derived from in vitro and animal studies, which may not fully translate to human health outcomes (Giordano et al., 2021; Shrinet et al., 2021).
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