Grapevine fanleaf virus: detection and distribution

The first three objectives of this study are dependent upon the fourth. That objective has been initiated with the establishment of the plant material in containers and the partial completion of the graft inoculations. We saved time establishing the plant materials by using rooted dormant cuttings supplied by the Department of Viticulture and Enologys field crew. These plants were potted into 1 gal containers and established. We also have ample numbers of additional established plants for re-grafting and to use as uninoculated controls. The majority of the rootstocks have been graft inoculated (see the table below) and we will soon begin another round of chip-budding. We will also use ELISA to assess the GFLV levels in the sample tissues both above and below the site of graft inoculation. The Muscadinia rotundifoliaand the Vitis berlandieri are now being propagated under mist conditions and may be graftable by Fall 1991. We sampled for fanleaf and tomato ringspot virus during the summer and fall of 1990 and found fanleaf widely scattered, but also found tomato ringspot in Napa, Sonoma and San Joaquin counties. We have resampled San Joaquin county this spring and with these results began to conclude this initial survey (the rough draft of a article for submission to California Agriculture article is included in Appendix 1). The incidence of TomRSV was higher than we expected, but does not pose a direct threat to the industry. TomRSV causes grapevine yellow vein disease, a disease which causes substantial yield reductions (on the order of fanleaf degeneration) on the east coast of the US. We suspect that this disease mimics fanleaf in California, but does not cause severe yield reductions. It is important for researchers and California Department of Food and Agriculture inspectors to recognize TomRSVs incidence and symptom expression to avoid confusion with fanleaf degeneration. Dr. Walker and Rowhani have completed a related research project determining which sample tissue produces the highest and most reliable ELISA reading over the course of the growing and dormant season (Appendix 2). Shoot tips and young leaves are the best sample tissue when growth is active, cambial scrapings of young phloem, cambium and young xylem are best after growth stops and before dormancy. During the dormant season actively growing tissues (shoots, callus, roots) forced from canes gave the highest values. We will use these results to best quantify the level of GFLV in the infected rootstocks. Elizabeth Frantz, a graduate student of Dr. Walker’s, is researching sampling strategies for GFLV detection in the vineyard. She completed sampling three 1225 vine plots with varying levels of GFLV incidence (low, medium and high) and is now testing each vine for GFLV with ELISA. We can then take the data and apply sampling strategies to it to determine how to best sample GFLV-infected vineyards.