Molecular Plant Breeding 2025, Vol.16, No.4, 241-249 http://genbreedpublisher.com/index.php/mpb 244 Figure 1 Schematic diagram of the monitoring system using Internet of Things (Adopted from Supriyanto et al., 2025) 6.2 Genetic markers linked to humidity tolerance and sugar traits Through the analysis of plant physiological responses and transcriptome, researchers found that some melon varieties that are tolerant to high temperature and high humidity have advantages in antioxidant enzyme activity, leaf water content and the expression of photosynthetically related proteins (Weng et al., 2022). These characteristics may be related to moisture resistance and sugar accumulation, and can be used as reference indicators for breeding moisture-tolerant and high-sugar varieties. There are also some graphical analysis methods like “genotype-trait-yield (GYT)” that can help identify good varieties with high yield and strong resistance (Rad et al., 2025). 6.3 Implications for breeding humidity-resilient high-sugar melon varieties Because different varieties respond differently to humidity, during breeding, good genes can be selected by combining molecular markers and some agronomic traits. By testing the sugar accumulation and stability of different varieties in multiple environments, it is possible to more quickly screen out those good varieties that can maintain stable high yields and high sugar content under various humidity conditions. This is of great help for the quality improvement and stress-resistant breeding of melons under facility conditions such as greenhouses (Weng et al., 2022; Neto et al., 2025; Rad et al., 2025). 7 Hormonal and Molecular Regulation Mediated by Humidity Signals 7.1 Hormonal crosstalk (ABA, ethylene) under high/low humidity Ethylene is an important hormone that controls the ripening of melons and the increase of sugar content. When the temperature is low and the humidity is high, ethylene synthesis decreases. For example, the expression of the CmACO1 gene will decline, thereby slowing down starch decomposition and sucrose accumulation (Lao et al., 2023; Guan et al., 2024). Some ethylene-responsive factors (such as CmERFV-2 and CmERFI-5) regulate genes related to ethylene synthesis and glucose metabolism, sometimes promoting and sometimes inhibiting, which directly affects the sweetness of melons (Gao et al., 2023; Yang et al., 2025). ABA (abscisic acid) is also related to sugar accumulation. Although its role in melons is not yet fully understood, in watermelons, studies by Durán-Soria et al. (2020) and Wang et al. (2023b) found that ABA-related genes (such as SnRK2.3) delay fruit ripening and affect sugar levels by controlling the synthesis of ABA and sucrose. 7.2 Expression patterns of sugar metabolism-related genes During the growth and ripening of fruits, the genes related to sugar metabolism constantly change. Genes such as sucrose phosphosynthase (CmSPS1), sucrose synthase (SS), acid or neutral invertase (AI/NI), and sucrose transporter (CmSWEET10) usually have increased expression levels near fruit ripening, which contributes to sugar synthesis and accumulation (Schemberger et al., 2020; Zhou et al., 2023). In different types of melons,
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