Tree Genetics and Molecular Breeding 2025, Vol.15, No.1, 1-8 http://genbreedpublisher.com/index.php/tgmb 4 4.2 Synergistic and antagonistic effects during fruit development Auxin and cytokinin interact in both cooperative and opposing ways during fruit development. Auxin plays a central role in the early stages, driving cell division and expansion, which are critical for fruit set and growth (Huang and Hong, 2024). Cytokinin becomes more influential in later stages, affecting nutrient distribution and fruit maturation. The relationship between these hormones is complex- auxin enhances ethylene biosynthesis, which accelerates ripening, as seen in the fast-ripening durian cultivar Chanee (Figure 2) (Hurny et al., 2020; Suntichaikamolkul et al., 2021). While auxin speeds up ripening, cytokinin is more involved in maintaining fruit quality and size. Figure 2 Fruit morphology during fruit development (Adopted from Suntichaikamolkul et al., 2021) Image caption: (A) whole fruit. (B) peeled fruit. (C) Arils across five developmental and ripening stages. Stage abbreviations: IM1, immature 1; IM2, immature 2; M, mature; MR, mid-ripe; R, ripe (Adopted from Suntichaikamolkul et al., 2021) 4.3 Environmental and genotypic effects on hormonal regulation Both environmental factors and genetic variations play a role in the hormonal regulation of durian growth and yield. Different durian cultivars display variations in auxin and cytokinin levels, influencing their growth and fruiting patterns (Fenn and Giovannoni, 2020). For instance, the Chanee cultivar has higher auxin levels during ripening compared to Monthong, contributing to its faster ripening process. Environmental elements such as temperature, sunlight, and soil conditions also impact hormone activity, ultimately affecting tree growth and fruit yield. Understanding these genetic and environmental influences is crucial for refining durian cultivation practices and boosting production efficiency (Cao et al., 2020). 5 Applications in Durian Breeding and Agricultural Production 5.1 Genetic improvement strategies for optimizing tree structure and yield Understanding the roles of auxin and cytokinin in durian growth offers opportunities to enhance breeding strategies. Identifying key auxin response factors (ARFs), such as DzARF2A, which regulate ethylene biosynthesis, allows for targeted genetic modifications to improve fruit ripening and overall yield (Khaksar et al.,
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