The Effects Of Exogenous Hormones IAA And GA₃ On Endocarp Hardening Of Walnut

Walnut（Juglans regia L.）is a typical economic woody oil crop with nutrient-rich fruit.The inner peel of walnut contains lignin,cellulose and hemicellulose,which can improve the mechanical strength of the shell and protect the integrity of the kernel.Incomplete shell development can easily lead to walnut kernel breaking,which is not conducive to walnut processing and transportation,and affects walnut fruit quality.Plant hormones gibberellin and auxin can regulate plant growth and development,promote lignin synthesis,and use exogenous hormones to avoid walnut’kernel’phenomenon,which is of great significance to promote the sustainable and healthy development of walnut industry and improve farmers’income.In this experiment,’Xinxin 2’and’Wen185’,two main varieties of Walnut in Xinjiang,were used as materials,and different concentrations of IAA and GA₃were used to spray the walnut,to explore the effects of different concentrations of IAA and GA₃on the lignin deposition of walnut inner peel and the contents of walnut shell components（lignin,cellulose and hemicelluloses）.The regulation effect of different hormones on walnut endocarp hardening was investigated by measuring the content of endogenous hormones in walnut endocarp,the content of related metabolites and enzyme activity in lignin synthesis.The correlation analysis was conducted on the contents of endogenous IAA and GA₃in walnut endocarp and the activities of enzymes related to lignin metabolism,and the relationship between different concentrations of exogenous hormones IAA and GA₃and walnut endocarp hardening was explored.The appearance index and intrinsic quality of mature walnut were measured,the effects of different concentrations of IAA and GA₃on walnut quality were analyzed,and the quality results were comprehensively evaluated by principal component analysis,and finally the optimal auxin or gibberellin concentration was obtained.In order to provide reference for further clarifying the mechanism of hormone regulation of walnut endocarp hardening,and to provide theoretical reference for rational use of"Wen185"and"Xinxin 2"walnut growth regulators.The results are as follows:（1）Different concentrations of GA₃and IAA can promote the endopericarp hardening of’Wen185’and’Xinxin 2’walnut,and low concentrations of GA₃and IAA have the best effect on walnut shell development.After different concentrations of GA₃and IAA treatment,the dyeing degree of endocarp of the two walnut varieties increased to different degrees,and the promoting effect was further proved by the determination of lignin,cellulose and hemicelluloses in the endocarp of walnut.The results showed that the contents of lignin,cellulose and hemicellulose in walnut inner peel increased with the increase of hormone concentration 10 days after hormone spraying,while 50 mg/L GA₃and IAA significantly increased the contents of lignin,cellulose and hemicellulose 17 days after hormone spraying.Different concentrations of GA₃and IAA treatment on walnut endocarp endogenous hormone content,lignin biosynthesis pathways of enzyme activity and the effects of the content of intermediate metabolites vary,endogenous IAA content was significantly associated with lignin and hemicellulose content,PAL,C4H and CAD and walnut endocarp composition show significant correlation,It is suggested that walnut endocarp hardening can be regulated by regulating endogenous IAA content and PAL,C4H and CAD activities.（2）Different concentrations of GA₃and IAA increased walnut fruit thickness and shell mechanical strength,and 50 mg/L GA₃and IAA treatments had the best effect.Principal component analysis showed that 50 mg/L GA₃treatment had the highest comprehensive score.Different concentrations of GA₃and IAA treatment had different effects on the internal nutritional indexes of walnut.Principal component analysis showed that 100 mg/L GA₃treatment had the best internal quality of’Wen185’walnut,and 150 mg/L IAA treatment had the best internal quality of’Xinxin 2’walnut.The appearance index of’Wen185’and’Xinxin2’walnut treated with 50 mg/L GA₃is the best,and the comprehensive score of its influence on fruit quality is high.Therefore,the cultivation and management of’Wen185’and’Xinxin 2’walnut treated with 50 mg/L GA₃is recommended.