Disease Note.

A Viroid from Coleus Species in Brazil. M. E. N. Fonseca, Department of Vegetal Biology, University of Brasilia. L. S. Boiteux, R. P. Singh, and E. W. Kitajima. Department of Vegetal Biology, University of Brasilia; Agriculture Canada, Research Station, P.O. Box 20280, Fredericton, New Brunswick, Canada; and Department of Cellular Biology, University of Brasilia, 70919, Brasilia (DF), Brazil. Plant Dis. 74:80. Accepted for publication 8 September 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0080C.

During investigation of viroid diseases in Brasilia (OF), Brazil, a viroid infecting the Coleus blumei Benth. cultivar Amarelo was isolated from plants without diagnostic symptoms. Analysis by return-polyacrylamide gel electrophoresis (R-PAGE) of the nucleic acid preparations of young leaves revealed the presence of low molecular weight nucleic acids with mobility within the range of viroids; the isolated RNA was infectious. In comparative tests by fractionation on one dimensional PAGE or by R-PAGE, the Coleus viroid migrated faster than citrus exocortis viroid, potato spindle tuber viroid, and avocado sun blotch viroid, indicating either small size or a unique secondary structure. The viroid band was completely eliminated by ribonuclease treatment or alkaline hydrolysis, indicating its ribonucleic acid nature. Manual slash-inoculation of nucleic acids from plants containing viroid-like bands to seven viroid-free Coleus cultivars resulted in infection of three cultivars. Leaves of infected cv. Frilled Fantasy were slightly chlorotic, and those without bands had more purple pigment. The other two infected cultivars showed no symptoms. In Brazil, Coleus is usually propagated by cuttings, and it is possible that plants of cv. Amarelo came from a single source, because plants without viroid were not found in the Brasilia area.