| The current micropropagation procedure of Virus-free pear can not meet the need of pear tree production development, because of the difficulty on rooting induction and propagation coefficient in tissue culture. In vitro shoots of quince BA29, a dwarf rootstock of occidental pears, and Pyrus betulaefolia Bunge, a mainly rootstock of oriental pears in northern China, were taken as explants for rooting study. Effect of the factors such as the basal media, auxin, temperature, pH value, sucrose concentration, days of darkness culture, two-stage rooting protocol, the combination methods of days of darkness culture and two-stage rooting protocol on the root formation was studied, as well as the transplantation of different matrixes, hardening-off time, the relative humidity of the atmosphere, transplanting stage; the anatomical observation of the root primordia formation and development by paraffin section method in vitro; the elementary application of rooting ex vitro. The aim was to improve the rate of rooting and survival and the propagation technique system of pear rootstock on BA29 and Pyrus betulaefolia Bunge. The main results were as foliowes:1 The rooting rate of BA29 was about 60% on the condition that the optimum root medium was 1/4 QL + sucrose 20.0 g-L-1 + agar 6.0 g-L-1 + IAA 1.0 mg-L-1 + IBA 0.5 mg-L-1 + NAA 0.1 mg-L-1 and the optimum cultural method was darkness culture for 46 days and the optimum temperature was (25±2) / (23±2)°C 30±2 / (28±2)°C.2 The rooting rate of Pyrus betulaefolia Bunge was over 80% on the condition that the optimum root medium was 1/4QL + sucrose 20.0 g-L-1 + agar 6.0 g-L-1 + IAA 0.5 mg-L- 1 + IBA 1.0 mg-L-1 + NAA 0.1 mg-L-1 and the optimum combination cultural method was darkness culture for 26 days with auxin and conventional culture without auxin and the optimum temperature of (25±2) / (23±2)°C.3 The induced root primordia originated from division and differentiation of the parenchyma cells in vascular cambium developed into the adventitious roots. Genotype plays an important role in the efficiency of rooting time. The rooting time of BA29 was focused on the first 10 days cultured in the optimum root medium. The Pyrus betulaefolia Bunge had a longer duration of rooting time growing in the optimum root medium and had more number of roots than that of BA29.4 The transplanting survival rates of BA29 and Pyrus betulaefolia Bunge were above 90% on the condition that the optimum hardening-off times was 912 days and the suitable proportion transplant media was the combination of vermiculite, perlite, and nutrition soil ( Half mixed with 1/2 vermiculite + 1/2 nutrition soil, the other mixed with 2/3 vermiculite + 1/3 perlite ) and the best transplanting stage was April or/and November and the optimum transplanting temperature was about 20°C and the RH was above 80% in the first 7 days.5 The result of rooting ex vitro showed that vigorous seedling of shoot proliferation after hardening-off had a lower rooting rate than the shoot of no rooting afer root induction by miniplant cutting method and moisture retention. The latter had the rooting rate of about 50%, dipping them in the rooting hormone solution (IBA 20.0 mg-L-1 or NAA 0.5 mg.L-1) for one minite.
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