Study On Substance Selection And Treatment Techniques For Relieving Chilling Injury In Watermelon Seedlings

Watermelon enjoys a high-temperature and dry environment,but it is more sensitive to low temperature reactions,and most watermelon varieties are not cold-resistant.In the early spring and winter cultivation,low temperature has become one of the main factors limiting the growth and yield of watermelon.In this study,the watermelon varieties of’Academic University No.5’were used as materials,and watermelon seedlings were pretreated with exogenous substances,including bihu（BH）,calcium chloride（CaCl₂）,chitooligosaccharides（COS）,sodium hydrosulfide（NaHS）and rooting powder（RW）.Treatment methods include irrigation and foliar spraying.To study the characteristics of physiological,biochemical,chlorophyll content and antioxidant capacity changes of watermelon seedlings under low temperature stress,in order to screen out exogenous substances and treatment methods that can improve the low temperature resistance of watermelon seedlings.It is of great significance to early cultivation of watermelons in protected areas in early spring.The main results obtained of this study are as follows:1.Under low temperature stress,using different concentrations of NaHS and RW treatment rooted watermelon seedlings,we found that 0.1 mmol/L NaHS and 50 mg/L RW can significantly increase the leaf Pn,Fv/Fm and root activity,and the activity of enzymes（CAT,POD,SOD,APX,GR,MDHAR and DHAR）and the contents of antioxidants（AsA and GSH）,significantly decrease the content of MDA,H₂O₂,and the production rate of O₂.^-,slowing down the low temperature stress on watermelon seedlings’injury,and enhance the low temperature resistance of watermelon seedlings.2.Under low temperature stress,the treatments of 20 mmol/L CaCl₂ and 75 mg/L COS are the best way.They can increase Pn and the content of Chl a,Fv/Fm and AsA in leaves,reduce the content of MDA in leaves,and induce the increase of antioxidant enzymes activities,and remove reactive oxygen species,and alleviate the oxidative damage of watermelon seedlings under low temperature stress,and increase the low temperature resistance of watermelon seedlings.