First Reported Viral Disease of Swedish Ivy Caused by Alfalfa Mosaic Virus. J. E. Carroll, Cornell University Plant Disease Diagnostic Laboratory, Ithaca, NY 14853. R. Provvidenti, New York State Agricultural Experiment Station, Cornell University, Geneva, NY 14456. Plant Dis. 73:183. Accepted for publication 29 November 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0183C.
Plants of Swedish ivy (Plectranthus australis R. Br.) received by the Cornell University Plant Disease Diagnostic Laboratory from a Rochester, New York, commercial florist showed sunken necrotic ring spots and line patterns. Plants eventually recovered from these prominent symptoms, but new growth showed chlorosis, mostly confined to the margin of the leaves. The apparent causal agent was identified by immunodiffusion tests and diagnostic plant species (e.g., bean, cowpea, and pea) as alfalfa mosaic virus (AMV). In the greenhouse, Swedish ivy plants derived from cuttings of healthy plants were inoculated with isolates of AMV originally recovered from Swedish ivy, pea, Valerianella olitoria (L.) Poll. (1), and Ajuga reptans L. (2). All four isolates incited similar symptoms, consisting of very prominent local and systemic reddish brown sunken rings and oak leaf and linear patterns, accompanied by leaf malformation and plant stunting. This acute stage of infection was followed by a chronic stage, during which infected plants recovered from severe symptoms but continued to show some chlorosis and occasional necrotic spotting. All the Swedish ivy plants used in this study were assayed for AMV infection before inoculation and after the appearance of symptoms. During the unusually hot summer of 1988, AMY-infected plants showed prominent necrotic leaf scorching and scattered necrotic spots, whereas healthy plants under the same environmental stress were unaffected. This is the first report of AMY or any other virus affecting P. australis.