Effects Of Uniconazole And Grafting On Growth And Physiology Of Watermelon Seedlings Under Low Temperature Stress

Watermelon is originally produced in tropical Africa and is sensitive to low temperature.At present,low temperature has become one of the restricting factors for the development of watermelon facility cultivation and industrialized nursery.In this experiment,the effects of uniconazole on the growth and cold tolerance of watermelon seedlings were studied by spraying different concentrations of uniconazole and low temperature treatment of watermelon seedlings,and the appropriate concentration of uniconazole was screened;Seventeen pumpkin rootstocks were treated at low temperature to study the effect of low temperature on their cold tolerance,and the varieties of pumpkin rootstocks with cold resistance and non-cold resistance were screened out;The effects of uniconazole treatment on watermelon seedling growth and physiology were studied with the selected uniconazole concentration and pumpkin rootstock,and the physiological mechanism of the interaction between uniconazole and grafting to improve the cold tolerance of watermelon seedlings was discussed,which provided theoretical support and reference for relieving watermelon low temperature stress.The main results are as follows:1.After treated with uniconazole,the shoot growth of watermelon seedlings was inhibited to varying degrees,and the inhibition effect increased with the increase of uniconazole concentration;Low concentration uniconazole treatment could promote the main root length,total root length and root volume of seedlings in different degrees,after the concentration of uniconazole reached 50 mg·kg^-1,the treatment of uniconazole showed an inhibitory effect;Uniconazole treatment significantly increased the chlorophyll content,and as the concentration increased,it first increased and then decreased.With the increase of the concentration of the watermelon seedlings treated with uniconazole,the fresh weight root-shoot ratio first increased and then decreased,and the dry weight root-shoot ratio was significantly higher than the control group.2.Under low temperature stress,as the concentration of uniconazole treatment of watermelon seedlings increased,the fresh weight and dry weight of the underground parts increased first and then decreased.After the concentration of uniconazole reached 100mg·kg^-1,the treatment of uniconazole showed an inhibitory effect.After the treatment of uniconazole,the ratio of fresh weight root to shoot increased significantly.Uniconazole treatment of watermelon seedlings could significantly reduce chilling injury index.As the concentration of uniconazole increased,Fv/Fm,Y（Ⅱ）,and q N increased first and then decreased,r ETR gradually increased,and q L gradually decreased.Under low temperature stress,uniconazole treatment decreased MDA content and relatived conductivity,and increased soluble protein content,POD,CAT and SOD activities.3.According to the measured chlorophyll fluorescence parameters of 17 pumpkin rootstocks under room temperature and low temperature stress,the yichihei rootstock had the strongest cold resistance,and the huangjindadang rootstock had the worst cold resistance.4.Under low temperature stress,grafting significantly promoted the growth of watermelon seedlings,increased root-shoot ratio,decreased chilling injury index,increased Fv/Fm,Y（Ⅱ）,q N,r ETR,POD,CAT,SOD activity,and decreased MDA content,and cold-resistant rootstocks had better grafting effects than non-cold-resistant rootstocks.Under low temperature stress,the interaction of uniconazole and grafting significantly increased the dry and fresh weight,fresh weight root-shoot ratio and dry weight root-shoot ratio of grafted watermelon seedlings,decreased chilling injury index,increased Fv/Fm,Y（Ⅱ）,q N and r ETR of watermelon seedlings,increased POD,CAT,SOD activities and soluble protein content of watermelon seedlings,and decreased relative conductivity and MDA content.The interaction of grafting and uniconazole significantly improved the cold tolerance of watermelon grafted seedlings.The interaction of cold-resistant rootstock grafting and uniconazole was better than that of non-cold-resistant rootstock grafting and uniconazole.