Response To Chilling Stress And Cold-resistance Evaluation Of Walnut Cultivats And Superior Lines In Shaanxi Province

This paper focused on the cold hardiness of walnuts, mainly including three parts. Inorder to select the high cold-resistance walnut cultivars and superior lines, the cold-resistanceability of annual dormant branches of9cultivars and superior lines was evaluated firstly. Thesecond part was the late freezing disaster simulation test of Xiangling walnut seedlings tomake sure the cold tolerance of Xiangling seedlings. As a result, these two parts could help usto study the cold-resistance response and mechanism of walnut under chilling stress. Theinfluence of exogenous GA₃on walnut flowering phenology was studied in the third part toprovide theoretical basis for exploring measures to delay walnut female flowering phase.Draw the following main conclusions:（1） Walnut annual dormant branches were treated by atifical low temperature. The resultsshowed that the lower processing temperature, the higher relative electrical conductivity（REC） of branches, superoxide dismutase （SOD） activity, the free proline and soluble sugarcontent first increased then droped, while malondialdehyde （MDA） content increased first,then droped and increased last. With the lengthening of treatment time, REC and MDAcontent of branches increased, and SOD activity and soluble sugar content increased first,then droped and increased last. While, the content of free proline increased or first increasedthen droped. The range of ratio of free water to bound water of9cultivars and superior lineswas0.83¹.61, and the median lethal temperature (LT₅₀) was17.196²4.484, with significantdifference among different cultivars and superior lines. Through the correlation analysisamong different physiology indexes of walnut under low temperature stress, it showed thatthe response of walnut branches was an outcome of closely related action and the changes ofphysiological indexes under different treatment that treated with different low temperature forthe same time or different time at the same tempertare was not completely consistent.According to comprehensive evaluation based on subordinate function value analysis, thearray of cold-resistance ability of9cultivars and superior lines from high to low was LuW06-1, JinLong, Qingxiang, Qing-16, Xilin3, Qinglin, Qing7-2, Xiangling, Xiluo3.（2） Xiangling seedlings were treated with low temperature in the early and middle ofApril. The lower temperature, REC of seedling leaves treated both in the early and middle of April became higher. The highest REC of seedling leaves was87.85%and78.70%respectively, which were treated at-4℃after12h, however, after returning to roomtemperature REC was81.48%and46.74%respectively. Under different treatment, freeproline content of seedling leaves after returning to room temperature were higher than treatedwith12h. It interpreted that seedlings recovered itself during the temperature rising slowing,and the self-recovery ability of seedling leaves in the middle of April was higher than theearly.（3）Proteins from the branches of Lu W06-1, Xiangling and Xiluo3and leaves ofXiangling seedlings treated with chilling stress were studied by the polyacrylamide gelelectrophoresis （SDS-PAGE）. It was obviously found that electrophoretic protein patterns ofbranches and seedling leaves were different, but showed similar among cultivars andtreatments even though there were some differential protein bands. With the temperaturedecreasing, there was an addition in the expression of38.9kD and83.3kD in three cultivars（superior lines）. And there existed a new protein band of56.6kD in Lu W06-1at-30℃. Withthe treatment time increasing, the expression of87.9and75.3kD increased and reached themaximum level in Xiangling and Lu W06-1after36h, and the addition of57.1kD expressionwas only observed in Xiangling. But, the expression of32.8kD in Xiluo3was decreased withprolongation of the treatment time. There was a new protein band of42.5kD in leaves witheach treatment. With the temperature decreasing, there was an increasing in the expression of47.8⁴8.0kD. Band of86.3kD was only observed in leaves of seedlings treated with-2℃after12h at early of April. And, band of83.6kD was only observed in leaves of seedlingstreated with-4℃after12h at middle of April.（4） The ultrastructural characteristics of cells in the seedling leaves after low temperaturetreatment were observed. The following major changes were observed upon treatment at2℃after12h: phenolics aggregated around plasma membrane of the epidermal cells; mesophyllcell structure was complete; a few of chloroplasts were swollen and disordered. But theultrastructure of leaves which returned to room temperature after2℃treatment was similarwith the control group. Thus, it suggested that the injury of2℃was reparable. After treatingwith-2℃, part of mesophyll cell occurred plasmolysis, chloroplast outer membrane damaged,plasma membrane became concave. After12h treating at-4℃, the protoplast dehydrationappeared, protoplast shrank, and most of the parenchyma cells deformed. The chloroplastenvelope ruptured, the stroma disordered and the thylakoid system displaced. What’s more,the ultrastructure of leaves which returned to room temperature after-4℃treatment can’trescovered. It was clear that the injury of-4℃was irreversible. （5） In order to study the influence of exogenous GA₃on walnut flowering phenology,different concentration of gibberellin （GA₃） was sprayed on the9walnut cultivars. It wassignificant different among the content of3kinds of polyamines in mixed buds of differentcultivars. Besides, the content changes of polyamines after spraying GA₃were also different.The putrescine （Put） content in mixed bud of Xinjufeng increased with increment of GA₃concentration, and the content of Spd reached the peak under the concentration of100mg L-1treatment, and Spm content in mixed buds with every treatment were significantly higher thanthe control group. By investigating the following flowering phenology, it was found thattreating with appropriate concentration of GA₃can delay the flowering phase of Xiluo3,Luguang, Xingjufeng and Vina. The buding and full-bloom stage of female flowers ofXinjunfeng treated with100mg L-1GA₃were delayed to13d and16d, respectively.