Cold Hardiness and Physio-Biochemical Responses of Annual Branches in Five Early-Fruiting Walnut Varieties (Juglans regia L.) Under Simulated Low-Temperature Stress
2025
Zitong Ni | Haifang Hu | Guiqing Xu
As global climate change escalates, horticultural crops, especially walnuts, face increased vulnerability to frost damage. Cold hardiness&mdash:a crucial trait for survival&mdash:is influenced by complex physiological and biochemical mechanisms. This study assessed the cold hardiness of five walnut cultivars&mdash:&lsquo:Xinxin 2&rsquo:, &lsquo:Wen 81&rsquo:, &lsquo:Wen 185&rsquo:, &lsquo:Zha 343&rsquo:, and &lsquo:Xinzaofeng&rsquo:&mdash:under simulated low-temperature stress, focusing on differences in freezing tolerance. One-year branches were gradually cooled to temperatures as low as &minus:30 °:C. Key physiological metrics, including electrolyte leakage (EL) and regrowth (RG) potential, along with biochemical metrics like antioxidant enzyme activities and osmoregulatory compounds, were used to evaluate cold hardiness. A comprehensive cold resistance indicator, derived using the subordination function method, highlighted cultivar resilience. Results showed significant variation in cold tolerance, with &lsquo:Wen 185&rsquo: and &lsquo:Wen 81&rsquo: exhibiting superior resilience, while &lsquo:Xinxin 2&rsquo: was the most susceptible. Logistic regression analysis of relative electrolyte conductivity (REC) data estimated the semi-lethal temperature (LT50), identifying &lsquo:Wen 81&rsquo: as the most cold-tolerant cultivar (LT50 = &minus:21.73 °:C). Antioxidant enzymes and osmoregulatory compounds were crucial for maintaining cellular stability and recovery after freezing. These findings offer practical insights for breeding cold-resistant cultivars and strategies to mitigate frost damage.
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