Remission of the free-branching pattern of Euphorbia pulcherrima by tetracycline treatment

Antibiotic-mediated suppression of the free-branching (FB) pattern of comme rcially available poinsettia cv. 'Angelika' (Euphorbia pulcherrima) support s recent results that the causative agent responsible for branching is a ph ytoplasma. Scions of phytoplasma containing FB plants were treated with tet racycline at 100-1000 parts per million (p.p.m.). The plants grew monopodia lly and phytoplasmas were not detected for several weeks after grafting ont o restricted-branching (RB) poinsettia. After prolonged growth without anti biotic treatment, phytoplasmas reappeared in most plants which became FB ag ain and one plant escaped from phytoplasma infection. In some poinsettia pl ants, the FB morphotype developed before phytoplasmas were detected by poly merase chain reaction. For the cultivar 'Angelika' the same poinsettia bran ch-inducing (PoiBI) phytoplasma (X-disease group; subgroup H) was detected by restriction fragment length polymorphism analysis of 16S rDNA as previou sly found in the United States (Lee et al., Int. J. Syst. Bacteriol. 48, 11 53-1169, 1998).