Clonal selection of "Vermentino" grapevine in Tuscany

The increasing interest in the 'Vermentino' grapevine variety for production of white wine in the Tuscan coastal region resulted in the initiation of a research project that studied the effect of various agricultural practices and techniques on several parameters of this variety. Clonal selection constituted the first phase of the study. The effect of 'Vermentino' clones on cluster and berry size, bud fertility, plant vigour and disease incidence was visually studied over 3 years (1991-1993). Seventeen vineyards located in the Tuscan coastal area were used. Each vineyard consisted of plants derived from grafts of local scions which ensured extensive variation in cultivar population. ELISA tests were performed on 114 mother plants to test for the most important virus diseases. These tests revealed a low percentage of infection of arabic mosaic virus (ArMV), grapevine fanleaf virus (GFLFV) and grapevine leafroll virus, a midrange presence of grapevine virus A and grapevine fleck virus and a high percentage of infection by grapevine leafroll virus 3. Biological tests using indexing indicators performed after the ELISA test showed that all the plants were free from fanleaf virus, grapevine corky bark (GCB) and LN stem grooving (LN33 SG), while 22 and 35%, of the plants were infected with grapevine leafroll virus (GLRV) and grapevine fleck virus (GFkV) respectively. Out of 53 plants tested for GVA and KSG, it can be noted that on ten presumed clones (18.8%) no correspondence between virus and viruses was found. Thus 7.5% samples gave a negative response to GVA and positive to KSG whereas 11.3% showed a GVA positive and KSG negative response. Grapevine vein necrosis (GVN) virus was present on all the surviving plants tested, while the vein mosaic (VM) was absent. Recovery work started on ten presumed clone affected by fleck and stem pitting. Ampelographic and productive observations made over a three-year period showed extensive variability between clones in cluster, berry size, yield, time of ripening and sugar content. Ten clones found to be free from the main viruses will be suitable for homologation. The different agronomical performances of these clones have the potential to satisfy the specific climatic and enological requirements of the coastal Tuscan are