INFLUENCE OF REGENERATION METHOD AND TISSUE SOURCE ON THE FREQUENCY OF SOMATIC VARIATION IN POPULUS TO INFECTION BY SEPTORIA-MUSIVA

Septoria leaf spot and canker are serious diseases of many hybrid poplar clones in plantations established for biomass production. Developing resistant clones through breeding is the best long-term strategy to minimize tree damage caused by this disease. Tissue culture and somaclonal selection techniques may reduce the time needed to develop disease resistance in poplars. We used a single source clone of a hybrid Populus to determine the influences of explant tissue source and regeneration method on the frequency of somatic variation in disease resistance. Plants were regenerated adventitiously via shoots and somatic embryos from callus derived from several tissue sources and from axillary buds. The resulting plants expressed somatic variation in disease resistance in different frequencies, except for the plants regenerated from hardwood cuttings. Several regenerated plants from various tissue sources exhibited variant morphological phenotypes, providing further evidence of the instability of this clone when cultured in vitro. Although mutagenic effects of the culture regimes alone cannot be ruled out, results of this study suggest that the explant source and culture method influenced how frequently variant plants were recovered.