Research On Grafting To Improve Salt Tolerance Of Garden Chrysanthemum

Garden chrysanthemum is a huge variety of chrysanthemums,and plays an important role in garden landscape design and flower sea design.The increasing soil salinization has limited the application and promotion of ground cover chrysanthemum in many areas.Research proves that grafting can improve the resistance of plants,the proper combination of rootstock and scion is the key element for successful grafting.Therefore,screening rootstocks with strong salt tolerance and studying the mechanism of grafting to improve the salt tolerance of chrysanthemums are of great significance for using this technology to improve the salt tolerance of garden chrysanthemums.In this study,five species of Artemisia were evaluated for salt tolerance,and Artemisia annua L.,which had stronger salt tolerance,was selected as the rootstock,was used as the scion for grafting.and the chrysanthemum ’Zhongshan Yanhong’,was used as the scion for grafting.NaCl stress treatment of 120 mmol·L-1 was used to compare the changes of morphological indexes,physiological indexes and ion distribution of grafted seedlings,self-rooted seedlings and self-rooted chrysanthemums of ’Zhongshan Yanhong’,and combined with RNA-seq technology to analyze salt stress The molecular mechanism of the next graft affects the salt tolerance of chrysanthemum.The specific work and main results are as follows:1.Five species of Artemisia vulgaris,Artemisia vulgaris Variegate,Artemisia rubripes Nakai,Artemisia yunnanensis,Artemisia annua were studied.Subjects were treated under the conditions of 1/2 Hogland nutrient solution culture with different concentrations of NaCl(0,80,120,160 mmol·L-1).After 6 days of treatment,physiological indicators were measured.The method of combining principal component analysis and membership function was used to comprehensively evaluate the salt tolerance of 5 Artemisia species.The order of the salt tolerance of 5 Artemisia plants from strong to weak is:Artemisia vulgaris Variegate>Artemisia vulgaris>Artemisia annua>Artemisia rubripes Nakai>Artemisia yunnanensis,and the comprehensive evaluation values of Artemisia vulgaris,Artemisia vulgaris Variegate,Artemisia annua are similar.They are relatively salt tolerant and can be grafted as candidate rootstocks.2.The garden chrysanthemum ’Zhongshan Yanhong’ was used as the scion,and Artemisia annua was used as the rootstock for grafting.Then,the physiological characteristics of the self-root seedlings,self-root grafted seedlings and rootstock grafted seedlings of chrysanthemum under 120 mmL-1NaCl stress were analyzed,as well as the Na+and K+ion contents in leaves and stems.The results showed that:(1)the leaf damage rate of rootstock-grafted seedlings was lower than that of self-grafted and self-rooted seedlings of ’Zhongshan Yanhong’ under NaCl stress;(2)Under NaCl stress,the relative water content,malondialdehyde content,and proline content of the rootstock-grafted seedlings were lower than those of the self-grafted and self-rooted seedlings,and the chlorophyll content,SOD,and POD content were higher than those of the self-grafted and self-rooted seedlings;(3)under NaCl stress,the Na+ content in the middle,lower leaves and upper stems of rootstock-grafted seedlings was lower than that of self-grafting and self-rooted seedlings,the Na+ content in the lower part of the interface was higher than that of self-grafted and self-rooted seedlings.Studies have shown that when Artemisia annua is used as rootstock for grafting,the higher Na+ enrichment capacity of Artemisia annua stem reduces Na+ accumulation in the upper part of the grafting interface.At the same time,the interaction between the rootstock and the scion gives the grafted seedlings stronger photosynthetic properties and anti-oxidant ability.Therefore,the damage caused by ionic stress to the leaves of chrysanthemum is alleviated,and the salt tolerance of chrysanthemum ’Zhongshan Yanhong’ is improved.3.Transcriptome sequencing was performed on the leaves of the self-rooted,self-grafted and rootstock-grafted chrysanthemum ’Zhongshan Yanhong’ under the stress of 120 mmol·L-1 NaCl for 8 days.The results showed that,a total of 133567 unigenes were obtained in the transcriptome.under salt stress,1533,378,and 269 genes were differentially expressed in self-rooted seedlings,self-grafted seedlings,and rootstock-grafted seedlings,among which 59 DEGs were co-expressed,and 1294,131,and 100 genes were specifically expressed.Through GO functional enrichment and KEGG pathway analysis,it was found that grafting under salt stress affected the gene expression pattern of chrysanthemum ’Zhongshan Yanhong’ leaves,and screened genes that contribute to salt tolerance from differentially expressed genes and analyzed them,Such as inducing the regulation of transcription factors and hormone transduction,increasing the expression of osmomodulin and antioxidant enzyme genes,and inhibiting the degradation of chlorophyll.Fifteen genes selected at random were verified by qRT-PCR,and the results showed that their expression patterns were consistent with the transcriptome sequencing results.