Physiological Responses And Cold Tolerance Evaluation Of Kiwifruit During Overwintering Period

Kiwifruit is one of the four most successful artificial domestication fruit trees in the 20 th century,and its fruit is also one of the most consumed fruits in the world.China is not only the natural distribution center of kiwifruit,but also the center of kiwifruit industry.At present,the main variety of kiwifruit in Shandong Province is Chinese kiwifruit（Actinidia chinensis Planch）’Taishan No.1’.Single variety planting will lead to concentrated picking period and short shelflife,which seriously threatens the development of kiwifruit industry in Shandong Province.Therefore,the introduction of excellent kiwifruit varieties suitable for winter low temperature climate is particularly important for the development of kiwifruit industry in Shandong Province.Here,we selected 11 kiwifruit variteies（’Taishan No.1’,’Xuxiang’,’Cuixiang ’,’Hayward’,’Hongyang’,’Jinyao’,’Jinyan ’,’Jinhong 50’ and ’Qihong’,’Longcheng No.2’ and’Hengyou No.1’）to investigate their phenology,growth habits and fruit characters.According to the results of the investigation,’Taishan No.1’,’Xuxiang’,’Qihong’ and ’Longcheng No.2’were selected to evaluate the cold tolerance.Firstly,the branches of kiwifruit treated with natural overwintering and low temperature were selected to determine the physiological indexes,including cell membrane permeability（relative electrical conductivity and malondialdehyde content）,permeability regulators（soluble sugar content,soluble protein content and free proline content）and protective enzyme activity（superoxide dismutase,peroxidase and catalase）.The correlation of the above indexes was analyzed.The main results are as follows:1.In this research,with ’Taishan No.1’ kiwifruit as a reference,the phenological phase,growth habits and fruit characters of 11 species of kiwifruit were evaluated,and the ripening period,growth habit and fruit setting rate were compared Four varieties of ’Taishan No.1’,’Xuxiang’,’Qihong’ and ’Longcheng No.2’ were selected to evaluate their cold tolerance.2.In this study,the physiological parameters of four kiwifruit species（’Taishan No.1 ’,’Xuxiang’,’Qihong’ and ’Longcheng No.2’）which overwintered naturally were measured.According to the changes of the relative conductivity and malondialdehyde content,we found that there was a high correlation between the degree of cell damage and the low temperature of natural environment.Among them,the relative conductivity and malondialdehyde content of’Longcheng No.2’ and ’Taishan No.1’ changed slightly,while those of ’Xuxiang’ and ’Qihong’were larger.There was a strong negative correlation between soluble sugar content and superoxide dismutase activity in ’Taishan No.1’,and a correlation between cell injury degree and soluble protein content,catalase activity and peroxidase activity.Similar phenomena appeared in ’Qihong’ and ’Longcheng No.2’,but there was a low correlation between cell damage degree and peroxidase activity in ’Xuxiang’.It has a high correlation with soluble sugar.Based on the above data,it is found that under natural conditions,the cold tolerance of’Longcheng No.2’ and ’Tai Shan No.1’ is better than that of ’Xuxiang’ and ’Qihong’ in natural conditions.3.Because of the complexity of natural conditions,we further measured the physiological parameters of kiwifruit branches treated with different temperatures（4℃,-10℃,-15℃,-20℃,-25℃ and-30℃）.And we calculated the semi-lethal temperature of each variety by Logistic regression analysis according to the relative conductivity.Among them,the semi-lethal temperature of ’Longcheng No.2’ was the lowest,followed by ’Taishan No.1’,and the semilethal temperature of ’Qihong’ and ’Xuxiang’ were the highest.The various physiological parameters were correlated with temperature.After chilling stress treatment,it was found that there was a high correlation among the physiological indexes（except catalase activity）of’Longcheng No.2’,which was common in other varieties.The correlation differences among the physiological indexes of four kinds of kiwifruit indicated that there were differences in physiological regulation modes of each variety under the condition of low temperature.In summary,’Longcheng No.2’ has the strongest cold tolerance,but the fruit is the smallest and the commercial planting yield is low;’Tai Shan No.1’ has stronger cold resistance,large fruit and good quality,which is suitable for planting in Shandong area;’Qihong’ and ’Xu Xiang’have the worst cold tolerance,but fruit flavor quality is good.If it is planted in Shandong area,manual means are needed to assist in overwintering.