Comprehensive Evaluation Of Drought Resistance And Cold Resistance Of Different Germplasm Of Kiwifruit

Shaanxi is one of the main production areas of kiwifruit in China,and the drought in summer or freezing injury in winter are the main environmental factors restricting the development of kiwifruit in this area.Therefore,drought or low temperature resistance is one of the main target characters in breeding of kiwifruit in this area,and evaluation and selection of germplasm materials with good drought and cold resistance are the basis of breeding and cultivation.In this paper,the main cultivars currently cultivated in Shaanxi and the superior strains of kiwifruit selected by the team were used as materials.On the one hand,drought treatment was carried out in the growing season of kiwifruit to evaluate their drought resistance;on the other hand,the dormant branches were used as materials for low temperature treatment to evaluate their cold resistance,and the mechanism of their differences in resistance was preliminarily analyzed from physiological and biochemical aspects,the main results were as follows:1.Fourteen kiwifruit cultivars and their hybrid lines were selected and grafted with‘Hayward’as rootstock.The drought resistance of the aerial parts was evaluated under natural drought treatment under pot culture condition,the physiological and biochemical indexes were analyzed and compared on the 0 day,5 days,10 days and 15 days after stopped watering.The results showed that net photosynthetic rate,transpiration rate and total chlorophyll content of kiwifruit decreased with the extension of drought treatment time,the contents of Malondialdehyde（MDA）,Hydrogen peroxide（H₂O₂）and Relative electrolyte leakage（REL）increased,while the activities of Catalase（CAT）,Superoxide dismutase（SOD）,Peroxidase（POD）and the contents of Proline（PRO）increased first and then decreased,the contents of Abscisic acid（ABA）decreased at first,then increased and then decreased.By calculating the drought coefficient of each individual index,conducting principal component analysis and establishing the membership function,comprehensive evaluation of drought resistance of fourteen kiwifruit germplasms and their hybrid lines was carried out.The evaluation results were ranked from strong to weak according to the drought resistance:‘Jinkui’,‘Jinnong2’,16+22-6,17-16-8,16-18-5,‘Golden fruit’,17+24-5,‘Hayward’,17-5-3,4-2,17-5,15-1,17-8-3,18-4.The system clustering method was used to analyze the comprehensive score,these germplasm resources can be divided into three types:high drought resistance（‘Jinkui’）,medium drought resistance（‘Jinnong 2’,16+22-6,17-16-8,16-18-5,‘Golden fruit’）,low drought resistance（17+24-5,‘Hayward’,17-5-3,4-2,17-5,15-1,17-8-3,18-4）.2.Twelve kiwifruit cultivars and their hybrid lines were selected and treated at-4℃,-8℃,-12℃,-16℃and-20℃for 8 hours respectively,the relative conductivity of kiwifruit treated with low temperature was measured,and the critical semi-lethal temperature(LT₅₀)was calculated by fitting Logistic equation.Four kinds of kiwifruit,‘Xuxiang’,‘Qihong’,4-2,16+23-1,were selected to measure the physiological indexes of the branches after different low temperature treatments.The results showed that:with the low temperature treatment,the REL of different dormant branches of kiwifruit increased,the contents of PRO decreased,and the contents of MDA increased and then decreased,the activities of CAT and POD increased at first and then decreased,but the activities of SOD and contents of ABA did not low of change obviously.The cold hardiness of four resources was evaluated by conductivity evaluation method and subordinate function comprehensive evaluation method,the two evalution results were 16+23-1>‘Xuxiang’>4-2>‘Qihong’and the correlation between the two evaluation results was-0.973,which reached the significant correlation.The results showed that the conductivity method could be used to evaluate the cold resistance of kiwifruit instead of the subordinate function method.The cold resistance of twelve kiwifruit germplasm resources was evaluated by electrical conductivity method,the evaluation results were ranked from strong to weak:‘Hayward’,16+23-1,‘Cuixiang’,‘Xuxiang’,7-5,‘Maohua’,4-2,‘Golden fruit’,‘Qihong’,16-18-13,X-7,15-1.The semi-lethal temperature was analyzed by systematic clustering method,these germplasm resources can be divided into high cold resistance（‘Hayward’）,middle cold resistance（16+23-1,‘Cuixiang’,‘Xuxiang’,7-5）and low cold resistance（‘Maohua’,4-2,‘Huangjinguo’,‘Qihong’,16-18-13,X-7,15-1）.