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

Antibiotic-mediated suppression of the free-branching (FB) pattern of commercially available poinsettia cv. 'Angelika' (Euphorbia pulcherrima) supports recent results that the causative agent responsible for branching is a phytoplasma. Scions of phytoplasma containing FB plants were treated with tetracycline at 100-1000 parts per million (p.p.m.). The plants grew monopodially and phytoplasmas were not detected for several weeks after grafting onto restricted-branching (RB) poinsettia. After prolonged growth without antibiotic treatment, phytoplasmas reappeared in most plants which became FB again and one plant escaped from phytoplasma infection. In some poinsettia plants, the FB morphotype developed before phytoplasmas were detected by polymerase chain reaction. For the cultivar 'Angelika' the same poinsettia branch-inducing (PoiBI) phytoplasma (X-disease group; subgroup H) was detected by restriction fragment length polymorphism analysis of 16S rDNA as previously found in the United States (Lee et al., Int. J. Syst. Bacteriol. 48, 1153-1169, 1998).