关键词: 苹果, 幼树, 黄土高原, 砧穗组合, 根系发育和分布

Abstract: It is one of the key practices for the high efficiency mode of apple production to properly select and combine scion and rootstocks. Flower formation and plant shaping of apple sapling are the important indexes to evaluate their performances，which was closely related to the root distributions with these combinations. With three year young trees from 8 kinds of typical scion-rootstock combinations as its subjects，this study investigated root distributions with the different scion-rootstock combinations by sectoral digging and trenching. The results showed that：the root architecture of young trees from 8 kinds of typical scion-rootstock combinations were classified into five types，M dwarfing rootstock combinations，SH dwarfing rootstock combinations，vigorous rootstock combinations，M dwarfing interstock combina- tions and SH dwarfing interstock combinations. It showed that the roots of the apple saplings with three years distributed horizontally and vertically within the limits of 0–60 cm，and the further away from their trunks and the deeper into soil，the less dense they distributed. With the different scion-rootstock combinations，the longest roots were roots with diameters of < 2 mm，followed by roots with diameters of 2–5 mm，and the shortest roots were those with diameters of more than 10 mm. There were more thick roots and less fibrous roots with the arborescent seedling root stocks than with the dwarfing clone rootstocks. Among the dwarfing rootstocks，fibrous roots dominated with the M rootstocks and less with the SH and Qingzhen rootstocks. Of the trees，stem diameters and crown diameters，but significantly positively correlated with the branch number，short-shoot proportion and flower bud number. Evaluations of the scion-rootstock combinations in terms of flower formation and plant shaping indicated that in irrigation-available regions of the Weibei Highlands，the trees from the M rootstock and interstock were able to set fruits early and easy to shape；the trees from the SH rootstock were easy to shape and poorly performed in early fruit set；and the trees from the arborescent combinations performed most poorly in early fruit set，which was closely related to the root distributions with these scion-rootstock combinations.

Key words: apple, sapling, loess plateau, scion-rootstock combination, root development and distribution