Evaluation of Cold Tolerance of Seven Walnut Varieties

BACKGROUND: Winter injury often threatens phenology and walnut survival in late spring and winter in northern areas of China. OBJECTIVE: This study aimed at evaluating seven walnut varieties which have superior economic traits. MATERIALS AND METHODS: Mature functional leaves were observed by paraffin section and the related anatomical structure indices were measured. The stem segments were placed at six temperatures [4 (control), -10, -15, -20, -25, -30°C] for low temperature stress treatment, and the relevant indices were measured. RESULTS: The thickness of palisade tissue (PT), sponge tissue (ST) and the PT/ST of ' Wen185 ' was significantly higher than in ' Longboxiang 2 ' , ' Longboxiang 3 ' and ' Suizhuang ' . However, the leaf thickness (LT) of ' Longboxiang 3 ' was markedly lower than that of other varieties. With the decrease in temperature, relative electrolyte leakage (REL), proline (Pro) and soluble sugar content (SS) of all varieties increased, while superoxide dismutase (SOD) and peroxidase (POD) activities showed a rise and fall trend. According to the LT50, the cold tolerance of seven walnut varieties was ranked from high to low, viz. ' Yuanlin ' > ' Wen185 ' > ' Xiangling ' > ' Suizhuang ' > ' Qingxiang ' > ' Longboxiang 2 ' > ' Longboxiang 3 '. CONCLUSION: The variety ' Yuanlin ' can adapt to low temperature and should be widely promoted.