Comprehensive Evaluation Of Several Apple Rootstock In Yunnan Province

Apple is an important cultivated fruit tree in China,and its planting area and yield rank the first in the world.Yunnan is located in the southwestern border of China,with high altitude,low latitude and unique three-dimensional climate characteristics,which results in the scattered distribution of main apple producing areas.The apple orchards in Yunnan are mostly located in mountainous areas with poor soil,poor fruit quality and severe plant diseases and insect pests.Most apples are propagated by grafting.Rootstock is an important factor affecting the growth and development of scions,yield and quality.Therefore,selecting appropriate combination of rootstocks is an effective means to improve stress resistance and yield of fruit trees.In this paper,21 apple rootstocks were identified by DNA barcoding,and the growth,development,branch composition and graft compatibility of different rootstock-scion combinations were preliminarily evaluated,so as to provide materials for the evaluation and collection of apple rootstocks in Yunnan,and lay a theoretical foundation for the development and utilization of apple rootstock-scion combinations suitable for local cultivation in Yunnan.The main results are as follows:1.Trait investigation for apple rootstocksIn this paper,the tree,branch,bud,leaf and fruit traits of 24 apple rootstocks in main apple producing areas of Yunnan were investigated and statistically analyzed,revealing that although the growth of tree No.5-19 was weak,the one-year-old branches and internode length were short,which suggested good tree dwarfing Rootstock No.1-8 could be used as candidates for dominant rootstocks because of their early fruit maturity and good traits.Moreover,Malus rockii Rehd.and G935were investigated,showing that rootstock ML had shorter intemode length and better dwarfing effect.2.Identification of genetic relationship of Apple Rootstock ResourcesThe phylogenetic and evolutionary relationship of apple rootstocks were preliminarily determined by DNA barcoding.Six DNA barcodes were selected and analyzed for the identification of phylogenetic relationship,including matK,rbcL,ITS4,ITS2,trnG-trnS and trnH-psbA.The amplification efficiency of these six DNA barcodes was all over 90%and the success rate of sequencing was about 90%,indicating that these fragments had good generality in apple and could be used as candidate fragments for the analysis of apple rootstocks.Comparing the phylogenetic relationship with the known Malus plants,it was found that 4 out of the 21 resources were closely related to Malus sieversii,15 to Malus corolla,and 2 to Malus rockii Rehd.2.Analysis of graft compatibility of different rootstock-scion combinationsAdditionally,in order to screen suitable rootstock-scion combinations,two apple rootstock-scion combinations of rootstock ML and Malus rockii Rehd.were evaluated.The results demonstrated that the combinations of ML and Nagafu No.2,Malus rockii Rehd.and Red Fuji had good performance.