EFFECT OF VIROIDS ON GROWTH, YIELD, AND MATURITY INDEXES OF CABERNET-SAUVIGNON GRAPEVINES

The effect of viroids was tested by comparing shoot tip cultured (STC) , viroid-free Cabernet Sauvignon to STC vines reinoculated with two gr apevine yellow speckle viroids (GYSVd-1 and GYSVd-2) and hop stunt vir oid (HSVd-g), and to a commercial selection of Cabernet Sauvignon. Gro wth and yield components were measured over a three year-period (1991- 1993) on mature vines in the Napa Valley. On average, vegetative growt h was greater on STC vines as a result of heavier shoots. Viroids did not affect yield components but fruit of STC vines was higher in titra table acidity and lower in pH than STC + viroids. In these own-rooted vines, viroids do not cause recognizable ''disease.''