Objective High temperatures during e-commerce storage and transportation may adversely affect the commercial quality of Phalaenopsis orchids and restrict the sustainable development of the industry. This study aimed to preliminarily investigate the response characteristics and resistance mechanisms of different Phalaenopsis cultivars under high-temperature stress, and to identify key indicators associated with heat tolerance, thereby providing references for heat-tolerant cultivar selection and postharvest preservation technologies.

Method Four Phalaenopsis cultivars, 'Ruyu', 'Yuhong', 'Xiaozhuangshi', and 'Xiaoheidie', were used as experimental materials. A simulated high-temperature environment for e-commerce transportation (40℃ day/30℃ night) was applied for 72 h, with a normal temperature condition (28℃ day/22℃ night) as the control. Morphological and anatomical traits, ethylene metabolism, and redox homeostasis were analyzed. The heat injury index, floral organ structure, contents of ACC synthase (ACCS) and ACC oxidase (ACO), activities of superoxide dismutase (SOD) and peroxidase (POD) were measured to compare cultivar differences.

Result The heat tolerance of the four cultivars ranked as 'Xiaoheidie' (heat injury grade 1) > 'Xiaozhuangshi' (grade 2) > 'Ruyu' = 'Yuhong' (grade 4). The first two cultivars exhibited relatively mild symptoms, such as slight peduncle drooping or mild wilting of terminal flowers, and recovered within 24 h under normal temperature. In contrast, the latter two cultivars showed obvious flower wilting and bud abortion, resulting in substantial loss of ornamental quality. 'Xiaoheidie' and 'Xiaozhuangshi' possessed petals approximately 0.7 mm thick with a semi-waxy layer and peduncles 4.6-5.0 mm in diameter with higher lignification, indicating structural advantages. In contrast, the weakly heat-tolerant cultivars had thinner petals (0.38-0.50 mm), lacked a waxy layer, displayed loosely arranged cells, and had thinner peduncles with lower lignification. Under high-temperature stress, 'Xiaoheidie' inbibited ACO accumulation, whereas 'Xiaozhuangshi' upregulated ACCS content to accumulate ACC. Weakly tolerant cultivars exhibited abnormal or unresponsive enzyme contents, suggesting that the ethylene pathway may not be the key factor determining heat tolerance. No significant changes in SOD activity were observed among the four cultivars. However, POD activity in the weakly heat-tolerant cultivars decreased by 52% and 42%, respectively, compared with the control, whereas the basal POD activity in heat-tolerant cultivars was 2-3 times higher. The basal anthocyanin content in 'Xiaoheidie' reached 0.595 mg/g (FW) and decreased by 28% under high temperature, suggesting a compensatory antioxidant role. Malondialdehyde (MDA) increased significantly only in 'Ruyu' (by 7%), indicating that it may not be a sensitive indicator for screening Phalaenopsis under the simulated high-temperature transportation conditions used in this study.

Conclusion Significant differences in heat tolerance exist among Phalaenopsis cultivars. 'Xiaoheidie' and 'Xiaozhuangshi' exhibited stronger heat tolerance. The adaptation of Phalaenopsis to high-temperature stress during storage and transportation may depend on the synergistic effects of morphological structures and physiological regulation. In particular, petal waxy structure, peduncle lignification, POD activity, ACO content, and anthocyanin content were closely associated with heat tolerance and may serve as important reference indicators for screening heat-tolerant Phalaenopsis cultivars.