An Efficient Procedure for Plant Regeneration from Long-term-cultured Callus Tissue of Hybrid Poplar(Populus sieboldii Miq.*Populus grandidentata Michx.).

Abstract

Plant regeneration via shoot differentiation was achieved using calli derived from leaf or stem explants of four genotypes of hybrid poplar (Populus sieboldii Miq.×P. grandidentata Michx, Y-63, Y-78, Y-79 and Y-102). The callus was induced and maintained in the presence of 2.0mg/l 2, 4-dichlorophenoxyacetic acid (2, 4-D). A high concentration of 2, 4-D permitted the proliferation of friable calli from explants and supported the active growth of homogeneous callus tissue during subculture. In all the genotypes tested, more than 60% of the calli from explants regenerated shoot-buds when transferred to a modified Linsmaier and Skoog medium with 2, 4-D omitted and containing 0.2 to 2.0mg/l zeatin. However, as the calli were repeatedly subcultured, the frequency of shoot regeneration under these conditions was reduced to less than 2% within a year. To imporve the shoot regeneration from these calli, they were first incubated for two weeks on a medium without any growth regulators, and then cultured in the presence of 0.6mg/l zeatin. With this procedure, the calli from a genotype Y-63 differentiated shoot-buds with an efficiency of 36%, which was markedly higher than the value obtained for calli grown continuously, without any change in the zeatin concentration. With a similar procedure, shoot regeneration from calli was possible for all the genotypes tested. The regenerated shoots differentiated roots when grown in a medium supplemented with a low concentration of auxin, and developed into mature plants after transfer to soil in a greenhouse.