| Walnut is an important dried fruit and oil tree species in China.In the north of China,walnut planting and fruit quality are affected by the stress of freeze injury and pests in winter.In this study,the walnut varieties ‘Xifu 1',‘Zhonglin 1' and ‘Xiangling' were used as test materials.Foliar application of 20 mg/L sodium selenite(single selenium fertilizer),20 mg/L sodium selenite and 2.5 g/L zinc sulfate(selenium zinc combined application),20 mg/L selenium Sodium and 2.5 g/L of ferrous sulfate(selenium iron combined application),water(CK).The effects of different treatments on the stress resistance and fruit quality of walnut were studied by measuring the changes of protective enzyme activity,osmotic regulatory substance,phenolic substance content,and the effects on fruit appearance quality,internal quality,and content of mineral elements.It provides theoretical reference for the planting of selenium-rich walnut in low temperature area.The research results are as follows:1.Influence on cold resistance of branches: in this study,selenium fertilizer,selenium and zinc combined application,selenium and iron combined application can promote the cold resistance of walnut,and the effect of iron selenium combined application is the best.(1)When selenium fertilizer was applied alone,the contents of soluble sugar,soluble protein and SOD activity of walnut branches were significantly increased by 26.17%,34.58%,35.32%(P < 0.01);the contents of proline and MDA were significantly decreased by 56.68% and 18.92%(P < 0.01),respectively,compared with CK,which promoted the cold resistance of walnut branches.(2)When selenium and zinc were combined,the soluble protein content and SOD activity of the branches were significantly increased by 33.55% and 24.89% respectively(P < 0.01);POD activity was significantly increased by 14.39%(P < 0.05);MDA and proline contents were significantly decreased by 33.04% and 17.25% respectively(P < 0.01),respectively,compared with CK.(3)The contents of soluble sugar,SOD activity and ascorbic acid in walnut branches were significantly increased by 20.46%,27.05% and 29.61%(P < 0.01);the contents of soluble protein and proline were increased by 6.39% and 7.43%;the contents of MDA were decreased by 9.99%,respectively,compared with CK.The fuzzy membership function analysis was used for analysis,and the results showed that the treatment of cold resistance from strong to weak was: selenium and iron application,selenium and zinc application,single application selenium fertilizer,clear water(CK).2.Effect on the disease resistance of branches: in this study,single application of selenium fertilizer,selenium and zinc combined application of,and selenium and iron combined application of can promote the disease resistance of walnut,and the effect of combined application of selenium and zinc is the best.(1)When the treatment was sprayed with selenium fertilize,the total phenol,flavonoids,tannin,ascorbic acid content and PPO activity of walnut branches were significantly increased by 46.00%,102%,24.92%,28.93% and 55.25%(P < 0.01),respectively,compared with CK.(2)When the treatment was sprayed with selenium and zinc,the total phenol,flavonoids,ascorbic acid content and PPO activity of the branches were significantly increased by 67.56%,95.91%,26.91% and 110%,and the tannin was increased by 20.91%,respectively,compared with CK.(3)When the treatment was sprayed with selenium and iron,the flavonoid content and PPO activity of branches were significantly increased by 79.82% and 98.47%(P < 0.01);the total phenol and tannin were increased by 9.93% and 17.75%,respectively,compared with CK.The fuzzy membership function was used for analyzing disease resistance physiology,and the results showed that the treatment of disease resistance from strong to weak was: selenium and zinc application,selenium and iron application,single application selenium fertilizer,clear water(CK).3.Effect on the quality of walnut fruit: in this study,single application of selenium fertilizer,selenium and zinc combined application,selenium and iron combined application can all improve walnut fruit quality,and the effect of selenium and iron combined application is better.(1)When the treatment was sprayed with selenium fertilize,the single fruit weight and kernel weight in walnut fruit appearance quality were significantly increased by 12.20% ~ 16.60% and 5.83% ~15.69%(P < 0.05);the contents of soluble sugar and total phenol in fruit were significantly increased by 12.41% ~19.22% and 8.17% ~ 16.47%(P < 0.05);the contents of selenium,calcium and manganese in mineral elements were significantly increased by 4.67 ~ 7.19 times,49.73% ~ 51.83%,13.65% ~ 51.01%(P < 0.01);and the content of copper was significantly decreased by 3.39% ~ 17.21%(P < 0.05),respectively,compared with CK.(2)When the treatment was sprayed with selenium and zinc,the single fruit weight of walnut fruit was significantly increased by 9.01% ~ 14.24%(P < 0.05);the contents of soluble sugar,soluble protein,total phenol and flavonoids in intrinsic quality were significantly increased by 12.02% ~17.34%,7.12% ~ 27.17%,17.61% ~ 24.19% and 16.63% ~ 21.32%(P < 0.05);the contents of selenium and calcium in mineral elements were significantly increased by 4.15 ~ 10.81 times,21.03% ~ 39.34%(P < 0.01);and the contents of manganese and zinc were significantly increased by 7.55% ~ 32.18%,12.35% ~ 21.13%(P < 0.05),respectively,compared with CK.(3)When the treatment was sprayed with selenium and iron,the single fruit weight and kernel weight of walnut were significantly increased by 7.50% ~11.71% and 11.51% ~ 18.86%(P < 0.05);the contents of soluble sugar,soluble protein and total phenol in intrinsic quality were significantly increased by 18.50% ~19.10%,19.17% ~ 30.87%,and 6.52% ~ 16.18%(P <0.05);the contents of selenium,calcium and manganese were significantly increased by 1.85 ~ 12.65 times,27.52% ~ 50.43%,19.18% ~ 64.90%(P < 0.01);and the contents of iron were significantly increased by 14.35% ~ 26.61%(P < 0.05),respectively,compared with CK.The fruit quality was analyzed by principal component analysis,and the results showed that the treatment of walnut fruit quality from high to low was: selenium and iron combined application,selenium and zinc combined application,single application of selenium fertilizer,water(CK).To sum up,the foliar application of selenium fertilizer,selenium and zinc combined application,selenium and iron combined application can promote the cold resistance and disease resistance of walnut branches,significantly improving the walnut fruit quality.The effect of selenium and iron combined application is the best.Different treatments can significantly improve the selenium content of walnut fruits.However,further studies are needed by maximizing the selenium content of fruits within the safe edible range,and adjusting the concentration of iron,zinc and selenium to achieve optimization of walnut resistance and fruit quality. |
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