Objective   Morphological and physiological changes and waterlogging tolerance of three major peach cultivars in Zhejiang Province in response to flooding stress were studied.

  Method   One-year-old seedlings of early (Chunhong), mid (Shinkawa Nakajima), and late (Jinxiu) varieties of peaches grafted on Maotao rootstocks planted in pots were treated with or without simulated waterlogging. Phenotype, waterlogging index, and root cell anatomical structure of the plants were compared, and photosynthetic parameters, osmotic adjustment substances content, and antioxidant enzyme activities determined. Waterlogging tolerance of the cultivars was evaluated using the membership function and principal component analyses.

  Result  Prolonged waterlogging progressively damaged the tips of the peach plant roots showing lysed cortical cells with irregular air cavities, and the roots eventually rotted. As the waterlogging index continued rising the leaves also wilted, yellowed, and even shed. The index on Chunhong was significantly lower than those of Shinkawa Nakajima and Jinxiu. The leaf photosynthetic capacity was hindered by the waterlogging with significantly declined net photosynthetic rate (P_n), transpiration rate (T_r), and stomatal conductance (G_s), and raised intercellular CO₂ concentration (C_i). The Chunhong variety maintained a higher photosynthetic capacity than did either Shinkawa Nakajima or Jinxiu. Meanwhile, under the stress, the leaf cell membrane permeability continued to rise, while the contents of MDA and SS and the activities of SOD and POD increased initially and then decreased. The membership function and principal component analyses ranked the waterlogging tolerance of these cultivars as Chunhong＞Shinkawa Nakajima＞Jinxiu.

  Conclusion  Prolonged waterlogging could cause severe damages to the roots and photosynthetic function of the peach plants. The degree of tolerance to such stress varied significantly among the 3 cultivars, and Chunhong was seen most tolerant to waterlogging as shown in the pot experiment.