Evaluation of physiological indices in response to cold stress in four potato cultivars (Solanum tuberosum L.)

Introduction Cold and freezing temperatures can cause serious damage to the potato plant (Solanum tubersum L.) and decrease yield. In intense cases, the cold stress can even destroy the entire production. Most potato cultivars are sensitive to cold, and temperature plays a crucial role in their geographic dispersal. Physiological responses of plants to cold stress include increased calcium transfer, changes in membrane lipid composition, enhanced antioxidant capacity, and accumulation of osmotic protectors. Compatibility, which involves the aggregation of cold-protecting polypeptides and osmolytes, is the primary method that plants use to cope with cold stress. Cold-compatible plants often store higher levels of soluble carbohydrates in their underground tissues. This study was conducted to investigate the mechanisms of cold tolerance in four potato cultivars: Agria, Fontane, Arinda, and Santé, highlighting the importance of cold stress to potato plants. Materials and methods The study was conducted using a completely randomized design with four replications. The factors considered were temperature (4, 2, 0, -2, -4°C) and potato cultivars (Agria, Fontane, Arinda, and Sante). To evaluate the response to cold, six-week-old seedlings were transferred to a thermogradient freezer with darkness and a temperature of five degrees Celsius. The temperature gradually decreased at a rate of two degrees Celsius per hour, and the seedlings were exposed to the desired temperatures (-4, -2, 0, +2, +4 °C) for one hour. Two weeks after exposure to cold stress, the percentage of survival, plant height, and the highest shoot dry weight of the cultivars were recorded. The content of malondialdehyde (MDA), soluble carbohydrates, total phenols, proline, catalase enzyme activity, peroxidase, and superoxide dismutase were evaluated. The statistical analysis was performed using Minitab v.17.3.1 software, and mean comparison was conducted using Duncan's multi-range test at a five percent probability level with standard error. Results and discussion The results revealed that the survival rate in cultivar Santé significantly decreased with decreasing temperature. Cultivar Fontane exhibited a higher survival rate than other cultivars at a temperature of -4°C. The phenol content in cultivar Santé at -2°C was 81% higher than in cultivar Fontane. In cultivar Sante, the proline content increased fourfold as the temperature decreased from 4 to 0°C. In cultivar Fontane, the proline content increased with a temperature decrease from 4 to -2°C and then decreased with further temperature reduction. The soluble carbohydrate content increased with a temperature decrease in cultivars Santé, Arinda, and Agria, while it decreased in cultivar Fontane. Cultivar Santé exhibited the highest increase in MDA (malondialdehyde) content, whereas cultivar Fontane showed the lowest increment when the temperature decreased from 4 to -4°C. Regarding enzyme activities, the CAT (catalase) enzyme activity increased 9.2-fold in cultivar Santé at a temperature of 0°C. In cultivar Fontane, the highest CAT enzyme activity was observed at 2°C. The POD (peroxidase) enzyme activity showed the highest increase in cultivar Santé with a temperature decrease to -2°C. In cultivar Fontane, the SOD (superoxide dismutase) enzyme activity decreased with a temperature decrease to 2°C and then increased by 80% with further temperature reduction to 0°C. After exposure to cold stress, plant height decreased in cultivars Santé and Agria compared to the control, while it increased in cultivar Fontane with a temperature decrease. The highest shoot dry weight was observed in cultivar Fontane at a temperature of -4°C, whereas the lowest shoot dry weight was observed in cultivar Sante. Conclusion Generally, this study showed that cultivar Santé is more sensitive to cold than cultivars Agria, Fontane, and Arinda. On the other hand, cultivars Fontane and Agria were found to be more tolerant. The studied metabolites and antioxidant compounds of cultivar Fontane were more significant under cold stress conditions, indicating more efficient defensive mechanisms compared to other cultivars. This ultimately resulted in better cold tolerance for cultivar Fontane.