Physiological And Biochemical Characteristics Of Thick-skin Melon In Chilling Resistance And The Effects Of Exogenous Substances On Them

Chilling injury one prominent problem suffered in protected farming of thick-skin melon. In order to provide chilling-resistance breeding and chilling injury prevention and control in protected farming of thick-skin melon with theoretical basis and references, the study conducted the seed germination experiment of different types of thick-skin melon varieties at low temperature and then screened two of the varieties that presented the most different chilling resistances; and then it studied the effects of low temperature stress and exogenous salicylic acid, oxalic acid and abscisic acid on chilling resistance-related physiological and biochemical characteristics of thick-skin melon seedling;and the chilling resistance-related physiological and biochemical characteristics of thick-skin melon plants at different growth stages were compared. Its main results were as follows:1. 16℃was the optimal temperature for detecting chilling resistance of thick-skin melon varieties by low temperature germination; the averages of the membership functions developed in terms of germination vigor, relative germination rate and relative germination index were probably used as the integrative indexes for testing chilling resistance of thick-skin melon varieties by low temperature germination.2. Two varieties were tested by low temperature germination to have the most different chilling resistances; the one with the strongest chilling resistance was"Yujinxiang"and the other that presented the weakest chilling resistance was"Bailangua".3. After the two varieties were placed at 6℃for four hours and six hours, the seedlings of the variety with the weakest chilling resistance presented a larger increase in electric conductivity than those of the variety with the strongest chilling resistance; after they were placed at 4℃or 6℃for six hours, the seedlings of the variety with the strongest chilling resistance presented remarkably higher CAT and POD activities and solvable sugar in their leaves than those of the variety with the weakest chilling resistances. Therefore,6-hour placement at 4℃or 6℃could be adopted as the optimal conditions for biochemical and physiological testing of chilling resistance of thick-skin melon.4. The melon plants showed different sensitivities to lower temperature in different stages of growth. They were less sensitive to low temperature at the seedling stage and sensitive to low temperature at the flower bud forming stage and the fruit-setting stage, but their sensitivities did not differ greatly between the latter two stages. The values of the membership functions, which were developed in terms of the increment rates in the electric conductivities, the activities of defending enzymes (SOD, POD and CAT) and solvable protein contents of the leaves under low temperature stress, could be adopted as the integrative indexes for testing chilling resistance of thick-skin melon varieties.5. After their leaves were treated with salicylic acid, oxalic acid and abscisic acid, the seedlings of"Yujinxiang"and"Bailangua"got their chilling resistances significantly enhanced. Salicylic acid presented favorable effect in increasing chilling resistance of thick-skin melon by its spraying at the concentration of 5 mmol/L and better effect in increasing chilling resistance of the varieties with strong chilling resistances by its spraying at 7.5 mmol/L; Oxalic acid presented favorable effect in increasing chilling resistance of thick-skin melon by its spraying at the concentration of 10 and 15 mmol/L; abscisic acid presented favorable effect in increasing chilling resistance of thick-skin melon seedlings by its spraying at the concentration of 0.5 mmol/L and better effect in increasing chilling resistance of the seedling of the varieties with strong chilling resistances by its spraying at the concentration of 0.75 mmol/L.