Plant Gene and Trait 2025, Vol.16, No.4, 152-161 http://genbreedpublisher.com/index.php/pgt 158 9.2 Cultivar selection and experimental design In the fields of Mississippi, researchers selected nine different tea tree varieties, including ‘BL1’, ‘BL2’, ‘Black Sea’, ‘Christine’s Choice’, etc. To test their growth conditions, leaf morphology, composition changes and heat tolerance performance under the local climate (Zhang et al., 2020). In Zhejiang Province, local tea trees that are relatively heat-sensitive, such as ‘Longjing 43’, were used in combination with exogenous treatments like AMHA to conduct experiments on improving heat tolerance (Yang et al., 2023). These experiments usually set up control groups and treatment groups to compare the physiological changes of leaves, yield and tea quality. 9.3 Leaf functional and yield performance under heat stress Experiments have found that for those varieties that are relatively heat-tolerant, under high-temperature weather conditions, the activities of antioxidant enzymes (such as POD, CAT, SOD) are higher, substances such as amino acids and sugars accumulate more in the leaves, and at the same time, the photosynthetic capacity is stronger and the leaf state is more stable (Huang et al., 2024). For example, after treatment with AMHA, the net photosynthetic rate and stomatal conductance of tea plants will increase, the damage to leaf cell membranes will be alleviated, and the growth recovery will be faster (Yang et al., 2023). In experiments conducted in the United States, different tea tree varieties performed differently in summer. Some varieties can maintain good yield and quality even at high temperatures, and the levels of substances such as polyphenols, amino acids and theanine are not low (Zhang et al., 2020). In addition, the use of black, blue or red shading nets can effectively reduce leaf temperature, improve the photosynthetic efficiency and growth rate of tea plants, and thereby maintain leaf function. 9.4 Farmer feedback and technology promotion potential These experiments demonstrate that planting heat-tolerant varieties, along with appropriate cultivation measures such as shading, spraying inducers or using new types of fertilizers, can indeed reduce the damage to tea trees caused by high summer temperatures, and also increase yield and the stability of tea quality (Lagoshina et al., 2021b). Local farmers also reported that practices such as shading and scientific fertilization are not difficult to operate and have good effects, and are suitable for promotion (Zhang et al., 2022). Furthermore, the selection and use of these heat-tolerant tea trees also provide a technical basis for emerging tea-growing areas like the southern United States (Zhang et al., 2020). 10 Concluding Remarks The heat tolerance of tea plants is mainly reflected in three aspects: gene regulation, metabolic response and physiological manifestation. From the perspective of molecular mechanisms, some heat shock proteins (such as HSP90, HSP70, HSP17.6 and HSP101) and their transcription factors (such as HSFA2) play a core role in tea plants’ response to high temperatures. They can help leaves retain water, maintain chlorophyll synthesis, stabilize cell membranes, and at the same time participate in signal transduction processes such as calcium and ethylene, thereby enhancing heat resistance. In terms of metabolism, heat-resistant varieties usually exhibit higher antioxidant enzyme activity at high temperatures and can accumulate more flavonoids, flavonols and other substances, which helps to eliminate reactive oxygen species in the body and reduce the damage caused by heat stress. Some tea tree varieties also have relatively obvious structural advantages in their leaves, such as a higher leaf mass per area (LMA). Such blades are less likely to be damaged in high temperatures and have more stable functions. From the perspective of field management, choosing the right variety, combined with reasonable irrigation, appropriate shading and scientific fertilization, can also significantly enhance the stability of leaf function of tea plants in summer and reduce the impact of high temperatures on growth and tea quality. However, most of the current research is focused on laboratories, and there is still insufficient understanding of the long-term effects in real fields and stability under different environments. Many experiments were conducted in greenhouses or under controlled conditions, failing to systematically analyze the interactions between different cultivation and management methods and tea tree varieties. Moreover, there is still not much data available to make a clear judgment on the direct relationship between the heat resistance of tea tree leaves and the final yield and quality.
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