Comprehensive Evaluation of the Physiological Responses and Cold Tolerance of Annual Shoots from Different Sweet Cherry (Prunus avium L.) Cultivars Under Low-Temperature Stress

Sweet cherry (Prunus avium L.) is a high-value horticultural crop; however, winter freezing injury significantly limits its introduction and stable production in cold-temperate regions. In this study, annual shoots of 16 major sweet cherry cultivars were collected during the dormancy phase and subjected to a simulated low-temperature gradient. Eight physiological indicators, namely, relative electrolyte conductivity (REC), malondialdehyde (MDA) content, osmoregulatory substances, and antioxidant enzyme activities, were systematically measured along with the poststress recovery growth percentage (RP). The semilethal temperature (LT50) was calculated using a logistic equation, and a multidimensional comprehensive evaluation system for cold tolerance was constructed using the membership function method, principal component analysis (PCA), and cluster analysis. The results indicated that low-temperature stress significantly induced membrane lipid peroxidation and osmotic compensation in the shoots. PCA revealed four principal components—osmoregulation potential, cell membrane damage threshold, cold-protective protein synthesis, and membrane stability—with a cumulative variance contribution rate of 79.47%. Correlation analysis revealed no significant correlation between LT50 (reflecting thermodynamic survival capacity) and the recovery growth percentage (reflecting poststress regenerative capacity), suggesting that “passive endurance” and “active recovery” in sweet cherries are two relatively independent physiological processes. The comprehensive evaluation model classified the 16 cultivars into four cold-tolerance tiers: High Tolerance (Russia 8, Reid, Pacific Red, and Brooks); Moderate-High Tolerance (Tieton, Jiahong, Sandra Rose, and Rivedel); Moderate-Low Tolerance (Luyu, Rocket, Tamara, Lapins, Frisco, and Taisho-nishiki); and Sensitive (Summit and Kordia). The four-dimensional evaluation model developed in this study provides a scientific basis for cultivar selection in cold regions and offers a theoretical reference for the trade-off of traits in future molecular breeding for cold resistance in cherries.