Molecular Plant Breeding 2025, Vol.16, No.4, 231-240 http://genbreedpublisher.com/index.php/mpb 236 it interacts with ethylene. Khaksar and Sirikantaramas (2020) found through research that a gene called DzARF2A is significantly more expressed in the late stage of fruit ripening, which can promote the expression of more genes related to ethylene synthesis and accelerate the ripening of the fruit. This performance is more obvious in durian varieties with faster ripening speed. There are also some genes related to hormone metabolism, such as CYP88, CYP94 and CYP707, which belong to the cytochrome P450 family and are involved in the metabolism of hormones such as gibberellins, jasmonic acid and abscisic acid. The expression of these genes in different durian varieties is also different, and they may also be involved in controlling the ripening speed (Suntichaikamolkul et al., 2021). Ethylene can also affect the synthesis of volatile sulfides, thereby affecting the fragrance of durian (Pinsorn et al., 2024). 7.3 Selection for high-yielding cultivars in different regions When breeding high-yield durian varieties, different places usually adopt different methods according to local conditions. Fruit thinning (removing some fruits) can make the remaining fruits larger, longer, and thicker in skin, and can also extend the shelf life. A common practice is to thin out 25% or 50% of the fruits. However, this method does not significantly increase the total yield (Nicolas et al., 2019). In the Mekong Delta in Vietnam, local fruit farmers cover the soil with plastic and use compound fertilizers rich in potassium, magnesium, and calcium to improve soil nutrients, reduce the problem of uneven fruit ripening, and thus increase the pulp ratio and sugar content, making the quality of durian better and the yield more stable (Quyen et al., 2025). In addition to these methods, there are now some new technologies that can be used to grade fruits, such as Raman spectroscopy and microfluidic paper chips. These tools can perform non-destructive testing and judge the maturity and quality without cutting the fruit, which can reduce post-harvest losses and improve the efficiency of the entire industry chain (Mettakoonpitak et al., 2024; Wattanasan et al., 2024). 8 Case Study: Selective Evolution of Key Trait Genes in ‘Musang King’ 8.1 Background and historical selection of ‘Musang King’ “Musang King” (D197) is a very famous durian variety in Malaysia. It was selected from natural seeds at the end of the last century and has a history of more than 30 years. The flesh of this variety is golden in color, very soft to eat, with small seeds and a particularly strong fragrance. It is very popular in Malaysia and China. In the process of promoting this variety, people focused on selecting several characteristics, such as fragrance, edible rate (how much flesh), ripening performance (how many days to be delicious), etc. These characteristics gradually became the hallmarks of “Musang King”, which also shows that people selected these traits. As a result, the genes related to these traits were preserved in this variety and gradually fixed. This also promoted “Musang King” from a local fruit to a popular high-end durian. 8.2 Comparative genomics between ‘Musang King’ and other cultivars Scientists used whole genome analysis methods to compare “Musang King” with other durian varieties. The results showed that its genes related to fruit aroma, taste and disease resistance were significantly different from those of other varieties. The most prominent one is the MGL gene family that controls the sulfur taste. In “Musang King”, the number of this gene family has increased, especially a copy called MGLb, which is expressed very highly when the fruit is ripe. This explains its particularly strong sulfur aroma. In terms of pulp taste, some genes related to cell wall degradation (such as PG and PMEI) in “Musang King” are expressed more strongly, which makes its pulp soften faster and more delicate when ripe. In terms of disease resistance, “Musang King” also has a different genetic structure. The number and arrangement of disease resistance genes such as NBS-LRR are different from other varieties. This shows that it has undergone selection for resistance during the breeding process. 8.3 Key genetic modifications contributing to premium fruit quality The reason why “Musang King” is so delicious is related to the regulation of a series of key genes. The expansion and enhanced expression of the MGL gene are the reasons for its strong sulfur flavor. The two genes ACS and LOX affect ethylene and lipid metabolism, and also affect the fruit ripening speed and fragrance release. In terms of sugar content, genes such as SPS and INV are responsible for controlling the accumulation and decomposition
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