Abstract:

Objective: In this study, we measured the dynamic changes of photosynthetic physiological parameters, osmotic adjustment substances and protective enzyme system of mulberry leaves of different breeding methods under waterlogging stress. The main purpose of this study is to reveal the response strategies and differences of mulberry trees derived from different breeding methods to waterlogging stress, so as to provide a theoretical basis for the ecological restoration and sustainable development of mulberry under the adverse environment such as the water level fluctuation. Method: The seedlings of two mulberry varieties (SG and AY), which were reproduced by grafting (JJ) and cutting (QC), were selected as the test objects. and the waterlogging stress (YS) was simulated through covering a pot with another pot. The dynamic changes of photosynthetic parameters, chlorophyll content, osmotic adjustment substance content (soluble protein, soluble sugar, proline, malondialdehyde) and leaf protective enzyme activity (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase) were measured on 0 d, 3 d, 7 d, 12 d, and 18 d of the waterlogging treatment to explore the effects of different breeding methods on the response of mulberry trees to flooding stress. Result: 1) The chlorophyll content decreased with the increase of waterlogging days, and the chlorophyll content of different varieties was only slightly different (P>0.05); 2)The diurnal variation of net photosynthetic rate (P_n) of CK-treated leaves showed a bimodal curve, while the mulberry seedlings with YS treatment showed a single peak curve of diurnal variation of P_n. QC breeding had slightly greater P_n value than JJ breeding did (P>0.05). The dynamic changes of photosynthetic parameters (P_n, G_s and Tr) of mulberry leaves in all treatments showed a trend of first decline and then increase, and the P_n value of QC breeding was slightly greater than that of JJ breeding (P>0.05). 3) With the extension of waterlogging time, the content of osmotic adjustment substances in the leaves of each treatment showed a downward trend. 4)Mulberry in all treatments could remove reactive oxygen species and maintain growth by increasing superoxide during the entire flooding period, but the changes of peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) showed a downward trend. Conclusion: The waterlogging stress reduces photosynthesis of mulberry trees, but there are differences in photosynthetic capacity between seedlings with different breeding methods. The photosynthesis ability of QC breeding mulberry is stronger than that of JJ breeding in the waterlogging stress. With the prolongation of waterlogging time, the two mulberry varieties in this experiment do not reduce the osmotic potential by accumulating osmotic condition substances. The SOD is the main defensive enzyme of mulberry in response to waterlogging stress. As for the response speed to waterlogging stress, there is interaction between breeding methods and different varieties. SG seedlings bred by QC respond faster than that bred by JJ, while AY seedlings bred by JJ respond faster than that bred by QC. This experiment shows that SG is suitable for QC breeding while AY is suitable JJ breeding. Whether different breeding methods have an impact on the physiological and ecological response of other mulberry varieties under waterlogging stress still needs further research and verification.

Key words: mulberry, breeding methods, waterlogging stress, response difference