Preliminary Study On The Mechanism Of Grafting Promoted Gene Mutual Introgression Between Yellow Cassava SC9 And Waxy Cassava SC102

Cassava(Manihot elculenta Crantz)is a plant of the Cassava genus in the Euphorbiaceae family.It is a staple food for nearly 1 billion people in tropical regions such as Africa and Latin America,and is also an important food security guarantee for China.South China No.9(SC9)is a yellow edible cassava with rich nutritional value and β-carotene content.However,SC9 has a slightly higher amylose content and a slightly harder taste,which affects people’s eating taste and thus affects the sales of edible cassava.Therefore,this study aims to create a new cassava germplasm with low amylose content,soft and glutinous taste,and rich β-carotene to meet people’s eating taste.South China No.102(SC102)cassava,commonly known as glutinous cassava,has a high content of branched starch,a soft and glutinous taste,and good edible quality.However,SC102 has a low β-carotene content and low nutritional value.How to combine the excellent characteristics of SC9 cassava and SC102 cassava? Cultivate a new edible cassava variety with high amylopectin content,soft and glutinous taste,and rich in β-carotene.The cassava genome is highly heterozygous,resulting in severe segregation of offspring traits and a long breeding cycle;It is difficult to achieve the expected variety in a short period of time through traditional hybrid breeding methods.Grafting can promote the mutual infiltration of genes between rootstocks and scions through the fusion site of grafting,especially the horizontal migration of genetic material between rootstocks and scions,achieving the goal of adjusting growth potential,enhancing adaptability,avoiding pests and diseases,and improving yield and quality.Through cassava grafting technology,this study used cassava SC9 with yellow heart and cassava SC102 with glutinous nature as experimental materials,used each other as scions and rootstocks for cross grafting,cut the grafting fusion parts that had been grafted for 1 year,2 years and 3 years,planted them in the field,and analyzed 10 months later,created 9 new germplasm with good properties of cassava SC9 with yellow heart and cassava SC102 with glutinous nature,served the cassava industry,promoted rural revitalization,and assisted the "the Belt and Road" initiative.The research results are as follows:(1)By analyzing the starch content of grafted offspring grown from fused stem segments after 1 year,2 years,and 3 years of grafting,it was found that compared to the control SC9 and SC102,the starch content of root tubers in all grafted offspring plants significantly changed,but generally decreased.(2)Analyze the amylose content of grafted cassava plants grown from fused stem segments after 1,2,and 3 years of grafting.The amylose content of the root tubers of grafted cassava plants is between SC9 and SC102,with grafted cassava plants 3(SC9/SC102)＿SC9 is 17.19%,lower than the 25.08% of the control SC9.(3)Analysis of β-carotene content in the root tubers of grafted cassava plants showed that the grafted offspring plant 2(SC9/SC102)＿SC9 has the highest β-carotene content,reaching 4.31 μ g/g,significantly higher than the control SC9’s 3.15 μg/g.(4)The three-generation sequencing technology of the whole gene was used to analyze the differences at the genome level between the grafted progeny plants growing from the 2-year grafted fused stem segments and the SC9 and SC102 control groups,and determine the influence of grafting on gene infiltration.The results showed that the distribution of SNP mutation types,insertion or deletion length distribution of CDS region,and insertion or deletion length distribution of genome of the grafted progeny plants growing from the grafted fused stem segments were significantly different.Allelic differences were identified from 137474 genes,among which 16 important gene loci were speculated to drive gene infiltration in offspring plants of SC102 grown from grafting fusion segments;It is speculated that there are 18 important gene loci driving gene infiltration in the offspring plants of SC9 grown from the grafting fusion segment;Most of these genes have not directly interacted with each other.(5)Eighteen members of the WOX gene family were identified from the important introgression genes,and their effects on graft healing and affinity were analyzed.The results of q RT-PCR analysis showed that 18 members of the WOX gene family were expressed within one year after the cross grafting of SC9 and SC102 cassava.With the extension of grafting time,the number of WOX family members was gradually reduced.Some members of the WOX gene family were no longer expressed,and only WOX1,WOX4,WOX7,and WOX12 were continuously expressed.