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In many cases the diagnosis of a viral disease in perennial woody plants requires indexing by grafting on indicator plants. In the case of grapevine leafroll and corky-bark diseases, indexing requires 2 to 3 years for symptom recording. Both diseases are found in all grapevine-growing countries. It would therefore be advantageous to develop a sensitive, quick, and reliable diagnostic technique. Explant shoots infected with corky-bark were micrografted onto healthy indicator rootstocks and maintained in vitro. Typical corky-bark symptoms appeared on the indicator within 8 to 12 weeks. Osmotic stress, in vitro, induced by sorbitol, enhanced leafroll symptoms. Explants expressed symptoms after 2 to 3 months of growth on these media. The advantages of these techniques are: Rapid indexing, saving of space and labor, could be performed year-round. Further experiments are underway for adaptation of the micrografting to leafroll disease and the stress method for corky-bark disease.
Grapevine (Vitis vinifera L.) explant shoots indexed forcorky-bark and rootstocks from healthy LN33 indicator plants were sterilized and maintained in vitro. When infected shoot tips were micrografted onto LN33 shoots, typical corky-bark symptoms appeared in 8 to 12 weeks. We suggest developing this method further to replace the regular, 2-year indexing procedure.