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. `Angelikaʹ (Euphorbia pulcherrima) supports recent results that the causative agent responsible for branch- ing is a phytoplasma. Scions of phytoplasma contain- ing FB plants were treated with tetracycline at 100± 1000 parts per million (p.p.m.). The plants grew mono- podially and phytoplasmas were not detected for sev- eral weeks after grafting onto restricted-branching (RB) poinsettia. After prolonged growth without anti- biotic 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 `Angelikaʹ the same poinsettia branch-inducing (PoiBI) phytoplasma (X-disease group; subgroup H) was detected by restriction fragment length polymorph- ism analysis of 16S rDNA as previously found in the United States (Lee et al., Int. J. Syst. Bacteriol. 48, 1153±1169, 1998).