Effects Of Exogenous Melatonin,grafting And Their Interaction On Growth Physiology Of Watermelon Seedlings Under NaCl Stress

Watermelon is one of the most important melon vegetables in the world.In recent years,the secondary salinization of soil has become an important factor that hinders the watermelon production,and more and more serious.It has been found that grafting can improve the adaptability of crops in stress,and different rootstocks have great differences in resistance.At the same time,the application of exogenous melatonin may also enhance the tolerance of plants to stress.In this experiment,’Zao Jia’watermelon was used as scion and17 varieties of pumpkin as rootstock.The effects of different concentrations of exogenous melatonin and different application methods on the growth and physiology of watermelon seedlings under NaCl stress were studied.On the other hand,the salt tolerance of different rootstocks was compared,and the most salt tolerant and least salt tolerant rootstocks were selected for subsequent experiments.Finally,the effects of grafting and interaction with melatonin on the growth and physiology of watermelon seedlings under NaCl stress were studied..The main results are as follows:1.Under NaCl stress,melatonin treatment with 50,100,150μmol/L could improve the growth indexes of watermelon seedlings to different degrees,such as the maximum photochemical efficiency（Fv/Fm）,the actual photochemical efficiency（Y（II））,the electron transfer rate（ETR）,the photochemical quenching（q P）,the superoxide dismutase（SOD）,the peroxidase（POD）,the catalase（CAT）enzyme activity and the proline content,and at the same time the salt damage index,Non photochemical quenching（NPQ）and malondialdehyde（MDA）contents were decreased.All above these improved the salt resistance of Watermelon Seedlings.However,with the increase of melatonin concentration,the growth and physiological indexes,chlorophyll fluorescence parameters and salt resistance of watermelon seedlings gradually decreased,and the high concentration of melatonin increased the salt damage of seedlings.Therefore,melatonin treatment with 100μmol/L was the best.2.Under NaCl stress,the growth index,Fv/Fm,Y（II）,ETR,q P,CAT enzyme activity,transpiration rate（Tr）,net photosynthetic rate（Pn）,stomatal conductance（Gs）,proline,ascorbic acid（ASA）content of watermelon seedlings treated with spraying 100μmol/L melatonin were higher than those of root treatment,MDA,NPQ,intercellular CO₂concentration（Ci）were all reduced,and the alleviative effect of spraying treatment on watermelon seedlings was better than that of root treatment.3.Under NaCl stress,salt damage index and dry matter accumulation of 17 rootstocks increased gradually.Y（II）,ETR and q P of"Huang Jin Da Dang"were thehighest among all varieties.The NPQ of"Jiu Zhen Yi Hao"was the highest.The activity of SOD,POD,CAT and the content of proline in"Huang Jin Da Dang"were significantly higher than that in"Jiu Zhen Yi Hao",and the content of MDA was significantly lower than that in"Jiu Zhen Yi Hao".Comprehensive comparison showed that the most salt tolerant variety was"Huang Jin Da Dang"and the least salt tolerant variety was"Jiu Zhen Yi Hao".4.Under NaCl stress,rootstock grafting with strong salt tolerance could improve the growth indexes,Fv/Fm,Y（II）,ETR,q P,chlorophyll content,SOD,POD and CAT activities,half saturated light intensity（lk）,Pn,Gs,Tr,proline,ASA content,and reduce the salt injury symptoms,NPQ and MDA content of watermelon seedlings,so as to improve the salt resistance of watermelon seedlings.However,the salt tolerant varieties did not significantly improve the salt resistance of watermelon seedlings under NaCl stress.On the whole,the salt tolerance of watermelon seedlings could be improved by rootstock grafting.5.Under NaCl stress,the growth indexes,Fv/Fm,Y（II）,ETR,q P,chlorophyll content,SOD,POD and CAT activities,initial slope（alpha）,maximum electron relative transfer rate（ETRmax）,Pn,proline,ASA content of atermelon seedlings were increased with spraying100μmol/L melatonin and grafting combination,and the salt injury symptoms,NPQ,Ci and MDA content of the seedlings were decreased more than those of the single grafting or melatonin treatment,and the salt resistance of the seedlings was better than that of the single grafting or melatonin treatment.There was significant interaction effect on some indexes,and the effect of interaction between rootstock grafting with strong salt tolerance and exogenous melatonin was better.