Effects of dwarfing interstocks on morphology and carbohydrates and nitrogen nutrition of Yanfu No. 3 apple nursery trees

Abstract:【Objective】The quality of nursery trees for planting have a significant effect on productivity during the early years of newly established orchards. Dwarfing rootstock plays an important role in vig-or control, early production and low labor cost. The effects of different dwarfing interstocks on the growth characteristics, root architecture, storage carbohydrates and nitrogen nutrients of apple nursery trees were clarified, aiming to screen suitable rootstock-scion combinations and produce high-quality apple seedlings.【Methods】Apple scions of Yanfu No. 3 were grafted onto 14 dwarfing interstocks (M9, M9-T337, M9-Pajam 2, M26, MM111, Mac9, P1, SH1, SH6, SH38, SH40, GM256, GM310 and Liaozhen No. 2), the nursery trees propagated in vitro of Malus baccata were used as primary rootstock.The morphological indicators such as the height, stem diameter, internode length, root depth, and root width of different interstock seedlings were measured after harvest of the nursery trees. The harvested nursery trees of each treatment were sampled and separated into four parts: leaf, branch, interstem and root. The root morphology included the surface traits of the individual root axis, such as root length, sur-face area, diameter, volume, tips, forks and crossings. The root morphology and architecture analysis was carried out by WinRhizo system. The contents of soluble sugars, starch, free amino acids and pro-tein were measured in different parts.【Results】Different dwarf interstocks had significant effects on the plant morphology, root architecture and storage carbohydrates and nitrogen nutrition of Yanfu No. 3 apple nursery trees. The trunk cross-sectional area (TCSA) and the height of the Yanfu No. 3 nursery trees with SH1 and MM111 interstocks were larger and growth vigor was stronger, while the TCSA and the height of the Yanfu No. 3 nursery trees with M9 and P1 interstocks were smaller, and the growth vig-or was weaker. The TCSA and height of nursery trees with Mark 9 interstocks were between those of the nursery trees with MM111 and M26 interstocks, so Mark 9 could be considered as a semi-vigorous interstem rootstock. SH series interstock tended to induce stronger growth vigor of the nursery trees. SH1 interstock had the highest effect on inducing strong growth vigor of the nursery trees, followed by SH38 and SH6, then SH40. GM310 and GM256 had an effect on inducing weaker growth vigor of the nursery trees, similar to M9 and P1. The ratio of Liaozhen No.2 interstock and the primary rootstock was close to 1. The ratio of the scion and SH38 interstock was 1.21, while those of the scion and other interstocks were less than 1. The internode length of 1-year-old shoot of the scion on SH38 interstock was the largest, although it was not significantly different from those on M9, SH1, SH6, M26, M9- T337, Mac9, SH40, GM310. The internode length of 1-year-old shoot of the scion on P1 interstock was the smallest, although it was not significantly different from those on Liaozhen No. 2, GM256 and M9- Pajam 2 interstocks. The root-shoot ratio of the nursery trees with GM256 interstock was the highest, al- though it was not significantly different from those with Mac9 and Liaozhen No. 2. The nursery trees with P1 and M9-Pajam 2 interstocks had the smallest root-shoot ratio. The nursery trees with Liaozhen No. 2 interstock had the largest root length, tips, forks and crossings. The nursery trees with SH1 inter- stock had the largest root surface area and root volume. The nursery trees with SH40 interstock had the smallest root length, root surface area and forks. The nursery trees with M9 interstock had the smallest root tips and crossings. The nursery trees with M9-Pajam 2 interstock had the smallest root depth and width, root diameter, root volume, and higher root length, root surface area, tips, forks and crossings. The soluble sugar contents in the leaves and roots of the nursery trees were higher than those in the branches and interstock parts. The soluble sugar contents in the leaves and shoots of the nursery trees with SH1 interstock were the highest, although it was not significantly different from those with MM111 interstock. The soluble sugar contents in parts of the interstock and roots of the nursery trees with MM111 interstock were the highest. The soluble sugar contents in the leaves and shoots of the nursery trees with P1 interstock were the lowest. The interstock part of the nursery trees with M9-Pajam 2 interstock had the lowest soluble sugar content. The root part of the nursery trees with M9 interstock had the lowest soluble sugar content. The starch contents were negatively correlated with the growth vigor of the grafted apple nursery trees. The nursery trees with M9, P1 and M9-Pajam 2 interstocks had the higher starch content, while the nursery trees with MM111, SH38 and SH1 had the lower starch con- tent. The content of free amino acids in each part of the nursery trees with M9-Pajam 2 interstock was the highest, the contents of free amino acids in the leaves, branches and roots were significantly higher than those on other interstocks. There was no significant difference between Mac9 and P1 in the part of the interstocks. The leaves of the nursery trees with MM111 interstock had the lowest free amino acids content. The content of free amino acids in shoots the nursery trees with SH40 interstock was the low- est. The interstock part of the nursery trees with SH1 interstock had the lowest free amino acids content, while the content of free amino acids in the roots of the nursery trees with SH6 interstock was the low-est. The contents of soluble protein in the leaves of the nursery trees on MM111 interstock were the highest. The contents of soluble protein in the shoots of the nursery trees with all interstocks were not significantly different. The soluble protein contents in the interstock and root system of the nursery trees with SH1 interstock were the highest. The leaves of the nursery trees with Mac9 interstock' had the low-est soluble protein contents. The contents of soluble protein in the interstock part of the nursery trees with Mac9 were the smallest, while the contents of soluble protein in the root part of the nursery trees with SH40 were the smallest.【Conclusion】The dwarfing interstocks were in a state of sugar depletion and reduced cellular activity to control the tree size by holding excess starch reserves at the expense of both root and scion growth. The scion trunk cross-sectional area, interstock starch content, interstock free amino acids content, leaf starch content, tree height, root tips, root volume, internode length, leaf free amino acids content and root surface area could be used as important indicators for evaluating the quality of apple nursery trees. Based on fuzzy comprehensive evaluation model of trapezoid subordi-nate function, according to a comprehensive consideration of dwarfing ability, root characteristics and storage nutrition, the comprehensive character scores of M9-Pajam 2 was the highest, so the combina- tions Yanfu No. 3/M9-Pajam 2/Malus baccata was the best.