Manipulation of Source Plant Material for Improved Virus Elimination

The tissue culture therapy technique described is highly successful for elimination of grapevine fleck virus and GLRV-2 from actively growing Cabernet Sauvignon grapevines. An average of 98%of explants which developed roots and were transplanted to soil tested ELISA negative for both viruses. The success was not dependent on whether source material was from the greenhouse or field or the month of excision. Generally, tips excised in May and June from both sources had optimal growth and rooting which supports ours and other labs’ experience that vigorously growing source plants increases tissue culture success. Virus elimination, however, was similar over all months; GLRV-2 was not detected in any successful explants from infected plants. GFkV was detected in plants in the May, June and July treatments. We also tested a subset of plants that grew poorly, were red and vitrified in tissue culture, and which developed no or only small roots; 100%were infected with GLRV-2. These plants would not normally be advanced in a tissue culture therapy program. This suggests that the high success rate of tissue culture therapy for virus elimination may be due, in part, to stress on the explant produced by the process of excision and tissue culture, since 40 – 60%of the plants excised did not develop roots and were not tested. A final ELISA test will be conducted in the fall of 2000 to check the virus status of the 1998 plants. The 1999-2000 research plan has been accomplished on schedule. Grapevine shoot tips were excised from Cabernet Sauvignon clone 5 mother plants with the same virus status grown in the field and in the greenhouse in each month from May to July to compare virus elimination success. Field tips were not available for the months of August, September and October due early vine maturation. Some preliminary information is now available as detailed in this report. Observations were made on rooting, contamination, and incidence of red, vitrified tissue. Generally, as seen in the first year, tips excised from greenhouse source plants in June had optimal growth and rooting. In the next few months, disease testing of the 1999 explants will allow us to strengthen our conclusions on the relative unimportance of source and time of year on successful virus elimination by tissue culture.