| Six melon varieties,failing into three cultivars ,were used as test materials.All cultivars were made in the situation of sub-low temperature in night(8~15℃)and normal in daytime by changing cover materials at melon seeding stage.The effects of sustained sub-low temperature for 30 days in night(8~15℃)and normal in daytime on the physiological and biochemical indexes at seeding stage, and also on the indexes of fruit were studied. This study provided the reference for resistance study to sub-low temperature of three melon cultivars at seeding stage.Also provided theoretical basis for the selection of melon varieties ,which were suitable for spring planting in hefei ;and the selection of new melon varieties, which had better adaptability to sub-low temperature in hefei. The main results showed as follows:1 The height of plant, the stem diameter, the leaf area and the dry weight of all the treated melon varieties were less than CK.; the indexes of all the treated varieties increased with the extension of time,which showed the treated melon varieties had lower growth than CK. The height of plant, the stem diameter, the leaf area and the dry weight of thick-skinned and intermediate varieties were larger than the CK in early period and the difference was not obvious in later period , the leaf area had the opposite situation. Jiuqingmi had the best tolerance of sustained sub-low temperature, Jiucuimi and Jiuhongrui had the worst in six melon varieties.2 The electrolytic leakage and MDA content of all the treated melon varieties were higher than CK except Jiuqingmi.; the ratio of treatment and CK had no difference among cultivars in preceding stage and the thin-skinned type was the smallest latter. The content of Chlorophyll for the treatment was less than CK; the ratio of treatment and CK for the thin-skinned typewas higher than other types. The electrolytic leakage of the thin-skinned type was less than other types all the time; the MDA content of all the treated melon varieties increased all the time except Jiuhongrui ; there was no difference among cultivars in preceding stage and the thick-skinned type was the highest latter; the content of Chlorophyll for all varieties increased all the time; there was no difference among cultivars in pre-period and the thin-skinned type was the highest latter., Jiuqingmi had the best tolerance of sub-low temperature in the three indexes .3 The content of proline and soluble protein for all treated varieties was smaller than CK all the time; the rate of proline content for all treated varieties in pre-period was bigger than the late; the ratio of treatment and CK for soluble sugar content increased first and decreased latter. The proline content of treatment in pre-period was bigger than the late; the soluble protein content for all treated varieties decreased all the time except Jiuqingmi. The soluble sugars of treatments were higher than CK for all varieties in pre-period and lower later.4 Only in the thin-skinned type ,the CAT activity, POD and SOD activities for all treated varieties were higher than CK all the time; the CAT activity of thin-skinned type was higher than thick-skinned type in pre-period time and thin-skinned type was higher than the intermediate type; there was no obvious difference among cultivars for POD activities in pre-period time and thick-skinned type had highest activities latter; the SOD activity of thin-skinned type was higher than the intermediate type and there was no obvious difference among cultivars latter.5 The impact of sub-low temperature for melon fruit after recover.The weight per fruit and dry weight of treatments were smaller than CK. The soluble sugar of treatments was smaller than CK except Jiuhongrui. The effect of sub-low temperature on the weight per fruit for thin-skinned type was lightest and for the intermediate type was worst; The effect of sub-low temperature on dry weight of fruit for thin-skinned type was lightest.
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