Screening Of Waterlogging Tolerant Germplasm Resources And Research Of Physiological Mechanism In Actinidia

Actinidia is extremely sensitive to water stress because of its fleshy and shallow root system.Due to heavy annual rainfall and viscous soil in the South area of China and short-term torrential rain in the Northern China during summer,kiwifruit orchards with inadequate drainage tend to accumulate excess water because of the poor drainage,which leads to waterlogging stress on plant.As kiwifruit is mostly propagated by grafting,rootstock directly affects the growth and development of scions.However,waterlogging-tolerant rootstock breeding of kiwifruit does not receive enough attention at present.Waterlogging-tolerant rootstock of kiwifruit is still unavailable in production.In this study,in order to preliminary evaluate waterlogging-tolerance of kiwifruit germplasm resources,two-year-old potted-plants of 10 genotypes from four species Actinidia were treated with excess water to study the effects of waterlogging stress on plant growth.One genotype from each species of kiwifruit was selected as test materials,which were used to analyze physiological mechanism of waterlogging-tolerant kiwifruit by examing morphologic changes and physiological responses under stress.Then,according to the changes of each index in response to waterlogging stress,the waterlogging-tolerance of four genotypes of Actinidia was assessed by membership function.Finally,the selected waterlogging-tolerant kiwifruit ‘KR2' and common rootstocks were compared for the performace,while the ‘Zhongmi 2' was used as the scion,which aimed to study the effects of rootstock on waterlogging tolerance of scion.The main findings are summarized as follows:1.Screening of germplasm resources of kiwifruit for waterlogging tolerance: by comparing the morphologic changes of the plant,the waterlogging tolerance of four species Actinidia is varied in response to water stress.The result showed that Actinidia macrosperma and Actinidia valvata were more tolerant than Actinidia chinensis var.deliciosa and Actinidia arguta in response to water stress.2.Physiological responses of kiwifruits under waterlogging: With the waterlogging time,the waterlogging damage indexes of four species of Actinidia increased and the root activity decreased gradually.Three photosynthetic indexes(Pn,Tr and Gs)increased firstly and then decreased under waterlogging stress in general.The contents of O2-,H2O2 and MDA of ‘Yongfeng 1' and ‘15-13' increased significantly during waterlogging stress.However,the plantlets of ‘KR2' and ‘KR5' still basically kept healthy and maintained high root activity and high level of photosynthesis.The contents of O2-,H2O2 and MDA of ‘KR2' and ‘KR5' were almost stable during waterlogging stress,and there was no significant difference compared to the control.3.Comprehensive evaluation of membership function: The comprehensive evaluation value calculated from membership function of four kiwifruit genotypes ‘KR2',‘KR5','15-13' and ‘Yongfeng 1' were 0.753,0.720,0.303 and 0.298,respectively.Therefore the order of waterlogging tolerance of four kiwifruit genotypes was ‘KR2' > ‘KR5'> ‘15-13' >‘Yongfeng 1'.4.Analysis of physiological mechanism of waterlogging tolerant Actinidia genotype: the waterlogging-tolerant genotypes of kiwifruit have ability to alleviate active oxygen damage to maintain root activity during waterlogging stress,which ensures that the plant could maintain the function of root system.Healthy root can absorb water and nutrients from the soil effectively,which promots the normal growth of kiwifruit plants.Healthy leaves have strong photosynthetic capacity,which produce and accumulate carbohydrates.Then,the carbohydrate could be transported to the root and used as metabolic substrate,which benefit to maintain physiological functions of the root system.5.Effects of rootstocks on waterlogging tolerance of scion: the waterlogging tolerance of A.valvata ‘KR2' was stronger than common rootstocks,and the rootstock of A.valvata could significantly improve growth characteristics and photosynthetic ability of 'Zhongmi 2' under waterlogging.It was concluded that the rootstock of A.valvata enhanced the adaptability to waterlogging stress of 'Zhongmi 2'.