Abstract
There have been numerous reports of grapevine viroids, describing physical and biological properties suggestive of similar or identical molecular forms. With consideration of these properties and the application of random-primed and specific cDNA probes, four major groups of grapevine viroids have been defined. Designations which can be used to describe distinct viroids within the four groups include (i) CEVd-g, a grapevine isolate of citrus exocortis viroid, (ii) GVd-c, a grapevine viroid recovered from cucumber, and AGVd, Australian grapevine viroid, (iii) GYSVd-1 and GYSVd-2, two viroids inducing yellow speckle disease and (iv) HSVd-g, a grapevine isolate of hop stunt viroid.