Effects Of Different Exogenous Substances And Their Combinations On Growth Of Watermelon Seedings On Cold Stress

Watermelon（Citrullus lanatus（Thunb.）Matsum.et Nakai.）is one of the important horticultural crops in China,which is thermophilic and heat resistance,the most suitable temperature is 25～35℃.Low temperature and the cold snap during spring often occur in early spring cultivation,which will prevent the normal development of seedlings root.At the same time,the root viability will decrease,the aboveground growth will be blocked and the leaf photosynthetic rate will be reduced,which will seriously affect the formation,future growth and development of seedlings.At present,the effect of antichiling agent for watermelon on the market is not satisfactory.Therefore,studying the effects of different exogenous substances and their combinations on growth of watermelon seedings on cold stress can improve the cold tolerance of watermelon in early spring.In this study,the effects of leaf spraying with Trehalose,potassium dihydrogen phosphate and potassium fulvic acid on the low-temperature resistance of watermelon seedlings were studied by analyzing physiological indicators such as chlorophyll fluorescence,relative electrical conductivity,dry fresh weight,malondialdehyde content,chlorophyll content,root growth,root viability,and antioxidant enzyme activity,and the most suitable concentrations were screened.And it was further combined with methyl jasmonate（MeJA）,and the anti-refrigerant Bihu,which is commonly used in production as a comparison.After the greenhouses were planted in advance and the leaf spraying pretreatment was completed,various physiological indicators were determined to screen out the best combination,which provided a reference for the study of cold stress of watermelon and build a foundation for the research and development of related products.The main findings are as followes:1.After spraying watermelon leaves with 1.0,1.2,1.5,2.0 g·L^-1Potassium dihydrogen phosphate and followed by 10/7℃（day/neigh）,it was found that suitable concentration of Potassium dihydrogen phosphate pretreatment could increase the maximum photochemical efficiency and root viability of watermelon seedings,increase the dry fresh weight of seedings,reduce the relative electrical conductivity and malondialdehyde content of leaves,and enhance the cold resistance of seedings,among which 1.5 g·L^-1Potassium dihydrogen phosphate treatment had the best effect.2.After spraying watermelon leaves with 5,10,15,20 m M Trehalose and followed by 10/7℃（day/neigh）,it was found that suitable concentration of Trehalose pretreatment could increase the maximum photochemical efficiency and root viability of watermelon seedings,increase the dry fresh weight of seedings,reduce the relative electrical conductivity and malondialdehyde content of leaves,and enhance the cold resistance of seedings,among which 15m M Trehalose treatment had the best effect.3.After treated with 5000,6000,7000,8000 times diluted Potassium fulvic acid to the leaves of watermelon seedings and followed by 10/7℃（day/neigh）,it was found that suitable concentration of Potassium fulvic acid could increase the maximum photochemical efficiency and root viability of watermelon seedings,increase the dry fresh weight of seedings,reduce the relative electrical conductivity and malondialdehyde content of leaves,and improve the cold resistance of seedings,among which 7000 times diluted Potassium fulvic acid treatment had the best effect.4.The leaves of watermelon seedlings were treated with Trehalose+Potassium dihydrogen phosphate+MeJA,Trehalose+mineral Potassium fulvic acid+MeJA,Potassium dihydrogen phosphate+mineral Potassium fulvic acid+MeJA and Trehalose+Potassium dihydrogen phosphate+mineral Potassium fulvic acid+MeJA,and followed by 10/7℃（day/neigh）.It was found that the combination of Trehalose+Potassium dihydrogen phosphate+mineral Potassium fulvate+MeJA had the best effect on increasing the maximum photochemical efficiency and root viability of watermelon seedlings,increasing the dry fresh weight of seedlings,reducing the relative electrical conductivity of leaves and enhancing the cold resistance of seedlings.5.Under the circumstance of low temperature in the field,the combination of Trehalose+Potassium dihydrogen phosphate+Potassium fulvic acid+MeJA could reduce leaf conductivity,improve leaf chlorophyll content,antioxidant enzyme activity and root viability of watermelon seedings,and increase dry fresh weight and root growth.