The effect of various thidiazuron concentrations and 2,4-d exposure on somaclonal variation and shoot morphogenesis in birch

Abstract

In vitro propagation techniques have been used on many plant species with varying degrees of success. Several species of birch, a diverse group of ornamental and forest trees, have been propagated using these techniques. Birch plantlets have been produced from axillary shoots, organogeneic callus, and somatic embryos. Organogenic callus and somatic embryogenesis involve cultural conditions that promote rapid unorganized cell growth. The auxin, 2,4-D is frequently used in these cultural systems. This study examined the effect of 2,4-D exposure on the ability to regenerate birch shoots from callus using thidiazuron (TDZ) and compared the subsequent rate of somaclonal variation in the plants produced via organogenesis and axillary shoot proliferation. Callus tissue was cultured on medium supplemented with 10 uM 2,4-D and 1.0 uM BA for up to 24 weeks and then was transferred to media with varying concentrations of TDZ. A minimum concentration of 0.01 uM TDZ was required for shoot organogenesis to occur, but a higher frequency of regeneration was obtained with either 0.1 or 1.0 uM TDZ. The number of explants differentiating shoots increased with increasing time of exposure to TDZ. Exposure to 2,4-D delayed and decreased the number of calli producing shoots, and calli exposed to 2,4-D for 18 weeks or more rarely produced shoots regardless of the TDZ concentration or exposure. The formation of albino and chimeral shoots was highest on explants exposed to TDZ without prior exposure to 2,4-D. Rooting, acclimation, and field establishment was not influenced by either 2,4-D or TDZ exposure. More plants survived the stressful conditions in the field from treatments with prior exposure to 2,4-D than from either axillary shoot cultures or plants that had been exposed to TDZ only. Further work needs to be undertaken to determine whether the surviving plants are truly more stress tolerant and to determine if and how 2,4-D might be influencing this stress tolerance.