The Effect Of Exogenous Substances On Cold Tolerance Of Watermelon Seedling

One-third of the global land area is considered as potentially suitable for a farming.However, because of a variety of abiotic stress, only some10%of them are farmed. Lowtemperature is one of the most important abiotic stresses which limit growth, production anddistribution of agricultural crops. Every year significant losses can result from late coldspring and sudden frosts in fall. Watermelon[Citrullus lanatus (Thunb.)] is fond of hightemperature drying, less hardy.In recent years, with the rapid development of facility technique and adjustment ofindustrial structure, watermelon off-season and advancing cultivation area increased year byyear, so low temperature became the important limiting factor of watermelon production.Exogenous substances, such as Abscisic acid(ABA), Cytokinin, Salicylic acid, Scorbic acid,Proline, Hydrogen peroxide, etc, could directly or indirectly influence correlativelyphysiological and biochemical characteristics and the expression of genes in plant under lowtemperature, which plays a positive role in adapting adversity. Therefore, the study of theeffect of exogenous substances on the change of the physiological and biochemicalcharacteristics in watermelon seedlings, has important instruction meaning to explore aneffective method to improve cold tolerance of watermelon seedlings and early springwatermelon production.With three-leaf stage of watermelon the tested material, we studied the effects ofdifferent exogenous hormones and different concentrations of exogenous ascorbic acid on thephysiological and biochemical characteristics in watermelon seedlings after0d,1d,3d,5d,7dunder low temperature. The results were as follows:1. With chilling sensitive watermelon ‘linglongwang’ as the tested material, weinvestigated the effects of exogenous50mg/L1-Naphthaleneacetic acid(NAA),25mg/L6-Benzylaminopurine(6-BA),25mg/L Gibberellin-3(GA3),25mg/L ABA on chilling injuryindex, the main content of active oxygen and the activity of antioxidant enzymes ofwatermelon seedlings under low temperature stress. The results showed that appropriateconcentration of exogenous6-BA, GA3, ABA could effectively improve the activity of SOD,POD, CAT, slow down the acumination of H2O2and O˙ˉas well as MDA, mitigate thedamage of low temperature in watermelon seedling under low temperature stress, then strengthen the cold resistance of watermelon seedling. Furthermore, considering the cost andother issues,25mg/L6-BA could be applied to production. While NAA worked in theopposite direction.2. With chilling sensitive watermelon ‘linglongwang’ and cold tolerance watermelon‘M08’ as tested material, we studied the effects of different concentrations of exogenous A-scorbic acid (0,25,50,100,200mg/L) on the content of active oxygen, the activity ofantioxidant enzymes and Ascorbic acid-Glutathione (AsA-GSH) cycle of watermelonseedlings under low temperature stress. The results indicated that different concentrations ofexogenous AsA could increase the activities of SOD, POD, CAT, APX, DHAR, MDHAR, GR,the content of AsA and GSH, slow down the generation rate of O˙ˉand the content of H2O2and the acumination of MDA, mitigate the damage of low temperature in watermelonseedling under low temperature stress. And50mg/L showed the best effect in ‘linglongwang’,while50mg/L and100mg/L have the better effect in ‘M08’.