Involvement of Viroids in Grapevine Diseases: Impact on Clonal Variation, Vine Performance, and Wine Quality

Executive Summary Statement of Research Findings VIROIDS are small, transmissible RNA molecules restricted to plants which are associated with disease. Viroids are extremely resistant to thermotherapy but viroid-free plants can be obtained by culture of very small shoot tips. The viroids we have detected in California and European grapevines present an unusual relationship for any crop with virtually every vine containing viroids. The basic goal of this project is to determine the significance of viroids to the growth and productivity of grapevines and wine quality. The widespread occurrence of viroids in grapevines throughout the world clearly indicates that all vine characteristics as well as wine quality, have been observed through a viroid background. The considerable investment made to the Viroid Trial at Oakville is returning information essential to our understanding of the impact of viroids on vine performance and wine quality. The viroid-free vines we have established at Oakville are the first control materials planted to a viroid test in the world and are critical to monitoring the effect of viroids on vines. Additional commercial, experimental, and germplasm cultivars have been entered into the viroid-free vine program to identify specific materials sensitive to the effects of grapevine viroids. Experiments designed to define the role of the grapevine viroids in YELLOW SPECKLE and VEIN BANDING diseases have been initiated. These studies are critical to the identification of the specific viroids present in vines and the scope of the threat of these diseases.