Tree Genetics and Molecular Breeding 2025, Vol.15, No.1, 1-8 http://genbreedpublisher.com/index.php/tgmb 3 and development. These genetic regulators collectively influence flowering timing and fruit production, ultimately shaping yield outcomes (Zhao et al., 2023). The weight of a durian fruit is determined by multiple components, including pulp, peel, and seed (Figure 1) (Khaksar et al., 2024). Figure 1 Images of durian (Durio zibethinus L.) fruit: peduncle, peel (husk), aril (pulp), locules, and seed (Adopted from Khaksar et al., 2024) 3.2 Role of auxin in fruit set and expansion Auxin is a primary hormone governing fruit set and expansion. It promotes both cell division and enlargement, which are vital processes in early fruit development. In durian, auxin levels rise during post-harvest ripening, indicating its role in enhancing fruit size and quality through ethylene biosynthesis regulation. Auxin also interacts with gibberellic acid (GA) to further support fruit enlargement by coordinating cell growth and expansion. Its impact on fruit size has been observed in various plant species, where it influences endoreduplication-related cell expansion, leading to larger fruit (Su et al., 2014). 3.3 Influence of cytokinin on fruit number and size Cytokinin also plays a key role in determining fruit number and size. It regulates cell division and expansion, both of which contribute to overall fruit growth (Li et al., 2024). However, cytokinin levels must be carefully balanced, as excessive amounts can negatively impact cell expansion and hinder fruit development. In durian, cytokinin signaling likely interacts with other hormonal pathways to influence fruit yield, similar to other species where cytokinin oxidase/dehydrogenase (CKX) genes regulate fruit size (Di Marzo et al., 2020). 3.4 Potential genetic markers for high-yield durian varieties Identifying genetic markers associated with high-yield durian varieties can enhance breeding programs. Auxin response factors, such as DzARF2A, have been identified as potential markers due to their role in regulating ethylene biosynthesis and fruit ripening. Additionally, genes involved in cytokinin degradation, such as CKX, may serve as useful markers for selecting varieties with optimal fruit size and yield. Incorporating these genetic markers into breeding strategies could lead to the development of durian varieties with improved fruit yield and quality (Zhao et al., 2021). 4 Synergistic Role of Auxin and Cytokinin in Durian Growth and Yield 4.1 Hormonal balance in tree growth regulation Maintaining a balance between auxin and cytokinin is essential for durian tree growth. Auxin promotes cell elongation and division, while cytokinin regulates cell differentiation and organ formation. Their interaction helps coordinate tree growth, with auxin driving shoot and root elongation and cytokinin stimulating new shoot formation (Sharif et al., 2022). A well-maintained hormonal balance supports tree structure and health, ultimately influencing fruit production (Teh et al., 2017).
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