Evaluation Of Heat Resistance Of Muskmelon Germplasms And Alleviating Effect Of Exogenous Substances On Heat Stress

Melon（Cucumis melo）is one of the most important horticultural crops in China.As the greenhouse effect increased in recent years,high temperature fall frequent extreme weather,facilities melon cultivation in China mainly in spring and autumn,spring late cultivated in the greenhouse temperature is high,high early autumn,the growth of melon seedling stage and flowering fruit-bearing stage caused serious influence,which finally impact on the yield and quality of melon,high temperature stress affected facilities melon industry sustainable and healthy development.It is urgent to improve the heat resistance of muskmelon and alleviate the adverse effects of high temperature stress on muskmelon.At present,the main measures to solve the high temperature stress are to use various genetic methods to breed varieties with strong heat resistance or to use exogenous chemical substances to induce the high temperature tolerance of crops.In this study,the heat resistance of 25 muskmelon germplasm resources was evaluated firstly.Then,the effects of exogenous MT and CaCl₂ on the growth and physiological characteristics of muskmelon seedlings,as well as the fruit yield and quality under high temperature stress were studied using‘Nongdatian No.5’as the test material.The main results are as follows.1.To evaluate heat resistance 25 melon germplasm resources,at seedling stage,using artificial climate incubator for 4 d processing,high temperature stress,respectively,estimated the thermal pollution index of the seedlings and seedlings were measured plant height,stem diameter,relative water content,chlorophyll content,photosynthetic rate,relative conductivity and malondialdehyde content,relative calculation of indicators,using the method of subordinate function analysis,According to the value of membership function,the 25 muskmelon materials were divided into 4 groups,including 14 strong heat resistant germplasm,7 medium heat resistant germplasm,2 heat resistant germplasm and 2heat sensitive germplasm.2.Effects of exogenous MT and CaCl₂ on the growth and physiological characteristics of muskmelon seedlings under high temperature stress:Under high temperature stress,the growth of muskmelon seedlings was significantly inhibited,spraying exogenous MT and CaCl₂ had a certain promotion effect on the growth of muskmelon seedlings;The application of exogenous MT and CaCl₂ could increase the chlorophyll content of muskmelon seedlings.Under high temperature stress,spraying exogenous MT and CaCl2could increase the activities of antioxidant enzymes（SOD,POD,CAT）in melon seedlings,and remove excessive reactive oxygen,which showed that the content of hydrogen peroxide（H₂O₂）decreased and the production rate of superoxide anion（O2·-）decreased.The damage to cell membrane structure was reduced by relative conductivity and malondialdehyde（MDA）.The best treatments were 150μmol/L MT and 20 mmol/L CaCl₂.3.Effects of exogenous MT and CaCl₂ on the yield and quality of muskmelon under high temperature stress:After high temperature stress,the yield of muskmelon decreased significantly,spraying exogenous MT and CaCl₂ could alleviate the inhibitory effect of high temperature stress on the yield of muskmelon,and spraying 150μmol/L MT and 10mmol/L CaCl₂ had the best effect on increasing yield.Spraying exogenous MT and CaCl₂could significantly increase the contents of soluble solids,soluble total sugar,reducing sugar and soluble protein in melon fruits,and the optimal MT concentration was 150μmol/L,and the optimal CaCl₂ concentration was 20 mmol/L.