Molecular Plant Breeding 2025, Vol.16, No.4, 241-249 http://genbreedpublisher.com/index.php/mpb 241 Feature Review Open Access Regulation of Fruit Sugar Accumulation by Humidity Control Techniques in Protected Melon Cultivation Wenzhong Huang , Zhongmei Hong CRO Service Station, Sanya Tihitar SciTech Breeding Service Inc., Sanya, 572025, Hainan, China Corresponding email: wenzhong.huang@hitar.org Molecular Plant Breeding, 2025, Vol.16, No.4 doi: 10.5376/mpb.2025.16.0024 Received: 10 Jul., 2025 Accepted: 13 Aug., 2025 Published: 25 Aug., 2025 Copyright © 2025 Huang and Hong, This is an open access article published under the terms of the creative commons attribution license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Huang W.Z., and Hong Z.M., 2025, Regulation of fruit sugar accumulation by humidity control techniques in protected melon cultivation, Molecular Plant Breeding, 16(4): 241-249 (doi: 10.5376/mpb.2025.16.0024) Abstract This study discusses how controlling air humidity in protected cultivation can influence the sugar accumulation of melon fruits, explaining how humidity affects the transportation of photosynthetic products, the formation of fruit “sink”, the activity of enzymes related to sugar synthesis, and the expression of related genes. It also analyzes how humidity interacts with other factors, such as temperature and light. The performance of several different humidity management methods in actual planting was summarized. The response differences of different melon varieties under different humidity conditions were also compared, and their potential in breeding was discussed. This study aims to provide some theoretical and technical references for improving the quality of melons and promoting intelligent planting. Keywords Melon breeding; Humidity regulation; Sugar accumulation; Protected cultivation; Molecular regulation 1 Introduction The sweetness of melons is an important criterion for evaluating their quality and market appeal. Melons with high sugar content taste better, are more acceptable to consumers, and are also more expensive (Albuquerque et al., 2006; Freilich et al., 2015; Ren et al., 2023). Therefore, whether it is breeding or planting management, increasing the sugar content in fruits is an important goal. Protected cultivation such as greenhouses or plastic sheds can artificially regulate the environment (Sabir and Singh, 2013). It can help melons avoid bad weather and extend the planting time, which is conducive to increasing yield and quality. In this environment, temperature and humidity can be regulated to better meet the growth requirements of melons, thereby enabling better accumulation of sugar in the fruits (Buczkowska et al., 2023). This study mainly explored how to control air humidity in protected cultivation to influence sugar accumulation in melon fruits, and further analyzed the related physiological changes and molecular mechanisms. This study hopes that these results can provide some theoretical support and assistance in planting techniques for improving the quality and industrial benefits of melons. 2 Physiological Basis of Sugar Accumulation in Melon Fruit 2.1 Photosynthate production and translocation pathways The sugar in melon fruits mainly comes from the photosynthesis of the leaves. The sugars produced by leaves, especially sucrose, are transported through the phloem to “sink” sites such as fruits. This transportation process requires the collaboration of some sugar metabolism enzymes and sugar transporters to deliver sugar from the “source” (that is, the leaves) to the “sink” (that is, the fruits) (Ren et al., 2023). 2.2 Sink strength and carbohydrate allocation during fruit development Whether a fruit can consume more sugar mainly depends on its “sink strength”. “Sink strength” refers to the ability of fruits to absorb and store photosynthetic products. This ability will increase with the growth of the fruit and is also regulated by genes and hormones (Ren et al., 2023). During the growth of melons, the “sink strength” of the fruit gradually increases, enabling it to absorb and accumulate more carbohydrates. Key enzymes such as sucrose phosphosynthase (SPS) control the process of sucrose production and affect the amount of sugar (Gao et al., 2023). Therefore, changes in sink strength will directly affect the final sugar content and quality in the fruit.
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