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EFFECT OF CUTTING MEDIUM TEMPERATURES ON ROOTING PROCESS AND ROOT PRIMORDIUM DIFFERENTIATION OF HARDWOOD CUTTINGS OF TETRAPLOID ROBINIA PSEUDOACACIA CUTTING MEDIUM TEMPERATURES OF TETRAPLOID ROBINIA PSEUDOACACIA

In this study, to examine the effect of heat treatment on the rooting and root development of hardwood cuttings of the tetraploid Robinia pseudoacacia, cuttings of 1-year-old stems were taken from 3–year-old mother trees and treated with IBA solution (1000 mg/L) for 6 h, with water was as a control. Treated cuttings were rooted in heated or unheated nursery beds. Samples were collected on day ten after planting, and then for every five days. The bases of the cuttings were embedded in paraffin and sectioned before being examined under a microscope to determine whether there had been any morphological changes. We found no root primordia in the tissues of the hardwood cuttings of the tetraploid Robinia pseudoacacia before cutting. In the heated bed, adventitious roots originated from callus tissue and the junction between the pith rays and cortical parenchyma cells, and in the unheated bed, adventitious roots originated only from callus tissue. The rooting process involved callus formation, adventitious root formation and elongation; rooting occurred 5-7 days earlier in the heated cuttings than in the unheated ones, and rooting rates were significantly higher in the former 30 days and 50 days after cutting; the minimum effective accumulated temperatures for these three stages were 109.25 o C, 211.68 o C and 301.38 o C, respectively. Our results revealed that heating the soil can promote adventitious root formation, speed up the rooting rate, and cut the propagation period of the tetraploid Robinia pseudoacacia.