Parameters for evaluating dwarfing ability in apple rootstocks

The goal of this study was to evaluate parameters related to the dwarfing ability in apple rootstocks and to provide some effective parameters for pre-selection of apple dwarfing rootstocks.Paraffin-wax cut-section was used to analyze the anatomical structure of leaves.PPO/POD activity and total phenol content were determined spectrophotometrically.The level of endogenous hormones was measured with ELISA and Hierarchical Clustering Method was used to evaluate these parameters.The result showed that the length of annual shoots,ratio of palisade/spongy of leaves,POD activity and content of endogenous IAA and ABA were significantly different at level P0.05 among tested rootstocks.The mean length of annual shoots of dwarfing rootstocks((19.51±2.03)cm)was markedly shorter than that of semi-dwarfing rootstocks and of the vigorous rootstock;the same tendency was noted in parameters such as total phenol content of leaves((9.23 ± 0.29) mg/g),PPO activity of phloem in spring,endo-IAA level((22.72 ± 7.62) mg/g)and ratio of IAA to ABA(0.18 ± 0.05),while the ratio of palisade/spongy of leaves from dwarfing rootstocks(1.15± 0.12)was markedly larger than that from semi-dwarfing and vigorous rootstock.The activity of POD in young leaves,content of ABA in phloem((118.21±13.85) mg/g) from dwarfing rootstocks in fall were markedly larger than those of and semi-dwarfing and vigorous rootstocks.From the Hierarchical Clustering Method′,none of the above of palisade to spongy leaves′ and the ratio of IAA to ABA of phloem′ was useful in distinguishing dwarfing rootstocks from parameters could evaluate the dwarfing ability of apple rootstocks.A combination of two parameters: the ratio standard stocks.Therefore,the ratio of palisade to spongy of leaves more than 1 and the ratio of IAA to ABA of phloem less than 1 are combined to exclude the putative standard candidates at first,and adding another parameters will ensure the early selection of dwarfing rootstocks successfully.