Objective In order to evaluate the cold resistance of five early fruiting walnut varieties in Xinjiang, the annual walnut shoots of 'Xinxin 2', 'Wen 81', 'Wen 185', 'Zha343' and 'Xinzaofeng' were used as experimental materials to determine the effects of different low temperature treatments on their physiological indexes, so as to provide a reference for the study of cold resistance of walnut.

Methods Using artificial simulation of natural cooling, 5 varieties of dormant branches were subjected to low temperature (−10, −15, −20, −25, −30 ℃) stress treatment. Eleven physiological indexes, such as electrical conductivity, relative electrical conductivity, soluble sugar content, malondialdehyde content, water content, germination rate, catalase activity, peroxidase activity and proline content, were measured during the treatment.

Results With the decrease of treatment temperature and the increase of treatment time, the conductivity, relative conductivity, soluble sugar content, and malondialdehyde content showed a gradually increasing trend, while the water content and germination rate showed a gradually decreasing trend. Catalase activity, peroxidase activity, and proline content showed an increasing trend followed by a decreasing trend, while superoxide dismutase activity and soluble protein content showed an S-shaped curve change trend.

Conclusion 'Wen 185' had the best cold resistance, while 'Wen 81' had the worst cold resistance, and the low temperature tolerance ranking was: 'Wen 185' > 'Zha 343' > 'Xin Xin 2' > 'Xin Zhaofeng' > 'Wen 81'. These findings are helpful to further understand the physiological mechanism of walnut coping with low temperature stress, and can provide theoretical support for the breeding of cold resistance in Xinjiang early-bearing walnut.