Clonal selection of Vermentino grapevine variety in the Tuscan coastal area

The importance of the cultivar ‘Vermentino’, in the production of white wine in the Tuscan coastal area, has increased during the last years as indicated by the use as a main variety for the production of four IGT and twelve D.O.C. white wines, eight of them are varietal wines. In previous researches the ‘Vermentino’ variety proved to have the capacity to improve the quality of the Tuscan white wines. These indications suggested the opportunity to initiate a research project promoted by the Grosseto province (south of Tuscany) and supported from ARSIA, on clonal selection in the Tuscan coastal area. This work was performed following the current method on twenty-one vineyards and permitted to identify 115 mother plants. The ELISA tests performed on the presumed clones after a visual pre-selection in the vineyards revealed a low percentage of infection for nepovirus ArMV (1.7%) and GFLV (3.5%), while the presence of leafroll associated closterovirus was low for GLRaV1 (8.7%) but very height for GLRaV3 (49.6%). An intermediate situation was observed for GVA and GFKV, which values of infection varied respectively from 27.8 to 29.1%. The biological test with indexing on Vitis, executed only on some of the plants subjected to the ELISA test (50%), confirmed that vine choose during the visual phase, were fanleaf free, a disease easy to identify on the mother plants. Leafroll symptoms were observed on 22 % of plants tested and in almost all samples ELISA and biological tests gave very similar results, except few cases which suggested the presence of others clostervirus. Very high was the presence of the rugose wood complex especially for RSP (66.1%), but also the KSG presence was important (10.7%). On the contrary LN33 stem grooving and corky bark were absent. In addition it was not possible to find a close correspondence from the GVA and the presumed KSG response. At the end of sanitary tests twelve presumed clones, which resulted free from the main viruses as fanleaf, leafroll, rugose wood complex and fleck are suitable for homologation. Ampelographyc and bioagronomical observations, made during the 1995 through 1999 growing season on the experimental vineyard established on 1993 at Massa Marittima (Grosseto province), permitted to identify several biotypes of ‘Vermentino’ which differed in cluster and berry size, yield, time of ripening , berry sugar content and titratable acidity. Most of these presumed clones had loose or medium density clusters which weight ranged from 160 to 300 g, giving consequently a large variability on yield (from 1.6 to 3.5 kg for vine). Wines obtained from microvinification of single clones, performed for three years, were subjected to sensorial analysis using a non parametric structured sheet which was built from a panel using twelve descriptors (seven for aroma, 5 for taste and the overall appreciation). From the standardized data, subjected to factorial analysis, were obtained 5 new complex variables (factors), which represented around 61% of the total variability. Using a multiple linear regression a correlation between overall appreciation and the 5 factors was found. This permitted to estimate mathematically the overall appreciation from the evaluations of panel descriptors. The results obtained from this work suggest that the homologation of new clones of “Vermentino” having different characteristics could allow viticulturists to widen the possibility to choose clones to satisfy specific climatic, agronomic and enological requirements.