Construction Of Progeny Population Of Cross Between Apple And Weeping Trait Crabapple And Preliminary Genetic Analysis

Plant type is of great significance for plant growth and development.It is also a trait closely related to actual production and cultivation.It determines the tree structure of fruit trees and has an important impact on the growth trend and fruit quality of fruit trees.At the same time,it also affects the difficulty of fruit tree shaping and pruning and cultivation man-agement technology.So far,the types of apple plants are relatively single,which requires fre-quent opening angle,shaping and pruning,resulting in high production costs and limiting the development of apple industry to a certain extent.As a unique phenotypic characteristic of ornamental crabapple plant type,there is little research on vertical branch character in recent years.Ornamental crabapple is rich in plant types,belongs to the same genus as apple,and has a relatively close genetic background.After crossing the weeping trait varieties with ap-ples lacking plant type types,it is expected to transfer the weeping trait to apples,so as to re-alize the light and simplified cultivation of apples,enrich type of apple plant types,reduce costs,and provide a theoretical basis for the regulation mechanism and genetic characteristics of weeping trait plant types.In this experiment,two apple cultivars Malus pumila cv.Fu Ji and Malus hupehensis Rehd.Gala were used as female parent,and four crabapple cultivars‘E1S1’,‘E1S9’,‘Honghua chuizhi’and Malus.‘Redjade’were used as male parent,and the hybrid population was constructed.The results show that:1.After artificial cross pollination between crabapple and apple,the hybrid population showed obvious weeping trait characters,and the separation ratio of straight branch and weeping trait characters was mostly 3:1.Straight branch crabapple branches grow nearly up-right and upward,and the extension angle of branches is usually between 0°and 90°（0°in the direction of anti-gravity）;The weeping trait refers to the drooping or creeping growth of branches,and the extension angle is usually greater than 90°.The base angle and extension angle of branches in the form of weeping trait were significantly greater than those in the form of straight branches;After measuring and analyzing the growth indexes such as photo-synthesis and mineral elements,it is found that the weeping trait plant type significantly af-fects the photosynthetic physiology and other indexes of the plant.The growth angle of the branch has a certain correlation with the photosynthesis of the leaves.The photosynthetic in-dexes of the weeping trait tree shape are improved compared with the straight branch.The analysis of mineral elements shows that the mineral element contents of the two plant types are significantly different,the content of Magnesium in the leaves of straight branch plant type was significantly higher than that of weeping trait,and the content of a large number of elements in the leaves of a few hybrid combinations.The content of straight branch plant type was higher than that of weeping trait plant type.The content of other mineral elements in straight branch plant type was lower than that of weeping trait plant type,and the shape of vertical branch tree was higher than that of weeping trait.2.We randomly selected 167 pairs of SSR primers from the public database of apple.Af-ter screening,93 pairs of SSR markers with clear bands,rich polymorphism and meeting the requirements of cooperative map were obtained,which were used in the hybrid F₂ population’Fuji’×’E1S1’.A total of 42 markers were located on 10 linkage groups,with a total length of192.2c M and an average distance of 4.58c M.The results showed that the method of drawing genetic linkage map for the constructed hybrid population was feasible,which laid a founda-tion for the construction of precise genetic linkage map for the expanded population in the future,and provided a theoretical basis.3.After transcriptome sequencing analysis of weeping and straight branch leaves,it was found that the difference genes were significant,and the enrichment analysis mainly focused on the metabolic pathway,indicating that the formation reason of weeping trait was highly correlated with secondary metabolites.The regulation mechanism of weeping trait is jointly regulated by multiple pathways.Through the preliminary screening analysis of differentially expressed genes,ILR and LAC genes may be related genes involved in regulating the for-mation of weeping traits.Their specific action principle and regulation mechanism will be further studied.In conclusion,this study constructed a hybrid population,and preliminarily expounded the genetic mechanism of weeping traits through physiological determination,genetic linkage map and transcriptome sequencing of crabapple of different plant types in the offspring of the hybrid population,which laid a foundation for gene mapping and detailed mechanism analy-sis of weeping traits in the later stage,and provided a theoretical basis.