Abstract: The root physiological changes of two kiwifruit varieties,Actinidia valvata "Shuixiu"  and Actinidia chinensis "Hongyang",were investigated under artificial waterlogging treatments of 6 h (early stage),24 h (middle stage),and 120 h (late stage).The results showed that in the early stage of waterlogging,the malondialdehyde (MDA) molar concentration in the roots of Actinidia valvata "Shuixiu" was relatively high,but then remained at a low level.In the early and middle stages of waterlogging,the molar concentration of superoxide anion (O-2) in the roots of Actinidia valvata "Shuixiu" was relatively low.In the early and middle stages of waterlogging,the root activity of Actinidia valvata "Shuixiu" was relatively strong.In the early,middle,and late stages of waterlogging,the superoxide dismutase (SOD) activity in the roots of Actinidia valvata "Shuixiu" remained at a relatively high level.With the extension of waterlogging stress time,the catalase (CAT) activity in the roots of Actinidia valvata "Shuixiu" first increased and then decreased,while the peroxidase (POD) activity first decreased and then increased.The activities of the three antioxidant enzymes in the roots of the Actinidia valvata "Shuixiu" waterlogging treatment group were always significantly higher than those of the control group,and were also higher than those of the Actinidia chinensis "Hongyang" waterlogging treatment group overall.Actinidia valvata "Shuixiu" can rapidly respond to waterlogging stress and activate the antioxidant defense system in time to alleviate the oxidative damage caused by waterlogging stress,showing strong waterlogging tolerance.The above indicators of Actinidia chinensis "Hongyang" were basically opposite to those of Actinidia valvata "Shuixiu",showing weak waterlogging tolerance.

Key words: Actinidia valvata, Actinidia chinensis, waterlogging stress, root vigor, antioxidant enzyme activity