Shoot proliferation of curly birch (Betula pendula var. carelica) in vitro depends on the explant type

Three curly birch (Betula pendula var. carelica) explant types - whole plantlets developed in vitro, plantlets with removed apices, and plantlets with removed roots were cultured on basal and multiplication media with or without supplementation of 0.5 mg.l(-1) BAP. The best growth of lateral shoots occurred in the presence of exogenously added cytokinin on explants with removed apex. The presence of roots enhanced the number of lateral shoots regardless on the presence or absence of the apex. Root initiation on formed lateral shoots was significantly (P > 0.99) lower when the shoot length was less than 6 mm. Rooted shoots grew rapidly into vigorous plantlets which could be utilized again for the production of microcuttings with identical genotype in the same year.