Grapevine Viroids as Possible Factors in Disease, Clonal Variation and Wine Quality

The general overview of this project is to provide an understanding of the importance of the grapevine viroids to vine growth, productivity, and wine quality. In addition, viroids may provide a novel yet practical approach to “customize” vine growth and development to achieve such goals as the reduction in excessive vegetative vigor. VIROIDS were first identified in the 1970’s as causal agents of plant disease. It has been recognized that in some cases these sub-viral RNA molecules can be readily transmitted into receptive plant species without producing any apparent host plant reaction viewed as an expression of plant disease . Thus, the viroid-RNA can be considered as a transmissible yet non-infectious entity. Because of this condition, it is possible that the biological activity of a viroid may be expressed by altering a normal growth response of a plant. With our observation of a virtual ubiquitous occurrence of 1-3 viroids in all vines in California, the role of the viroids in grapevine tissue has become of interest. This unusual property of the widespread association of viroids with grapevines indicates that eyery vine characteristic including viticultural and enological property is viewed through a viroid background. Many of the accomplishments that have been achieved in this project have been published (enclosure copy of Szychowski et al., Vitis 30, 25-36, 1991) or presented in Sept. 1990 at the 10th Meeting b7 the ICVG (International Council for the Study of Viruses and Virus Diseases of the Grapevine) and at the Annual Meeting of the ASEV in June, 1990. These reports provide information concerning: 1) The first field trial of viroid-free grapevines now in the fourth growing season at the Oakville Experiment Station. 2) The commonality among the grapevine viroids from California and Europe. 3) The production and propagation of viroid-free varietals and rootstocks. 4) The comparative properties of viroids from grapevines which relate to the incidence of yellow speckle and vein banding diseases.