VIEW ARTICLE

Etiology

Association of Viroids with a Graft-Transmissible Dwarfing Symptom in Australian Orange Trees. Mark W. Schwinghamer, Visiting Scientist, New South Wales Department of Agriculture, P.M.B. 10, Rydalmere, N.S.W. 2116, Australia, Present address: New South Wales Department of Agriculture, Agricultural Research Centre, Tamworth, N.S.W. 2340, Australia; Patricia Broadbent, Senior Research Scientist, New South Wales Department of Agriculture, P.M.B. 10, Rydalmere, N.S.W. 2116, Australia. Phytopathology 77:205-209. Accepted for publication 26 May 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-205.

Orange trees (Citrus sinensis on Poncirus trifoliata rootstock) dwarfed by graft-inoculation in earlier field trials were tested to determine if viroids were associated with dwarfing symptoms. Uninoculated trees without dwarfing symptoms were used as controls. Trees dwarfed with any of three sources of inoculum (isolates) gave positive results in three types of test for viroids, namely, symptom development in citron (C. medica), gynura (Gynura aurantiaca), and tomato (Lycopersicon esculentum), hybridization with a nucleic acid probe specific for citrus exocortis viroid (CEV), and polyacrylamide gel electrophoresis of nucleic acid extracts. Four other isolates gave mild viroidlike symptoms in citron and some faint hybridization reactions, but negative results in the other tests. The results suggest that viroids are consistently associated with dwarfing, that CEV is present in at least some cases, and that viroids that are harder to detect than (and possibly distinct from) CEV are present in other cases.