Radiometric properties, vine physiology and yield parameters of irrigated ‘Sublima’ table grape under different plastic films in South Italy

Covering plastic materials are used to protect vines and grapes from adverse weather conditions and to influence the microclimate, aiming at modifying the growing conditions in comparison with those in open field. This technique may advance or delay berry ripening in table grapes according to the period of covering. The radiometric properties of the plastic covering films influence canopy microclimate, leaf functioning, yield components and berry quality of grapevines. Three polyethylene films were tested in Southern Italy during the 2012 season: two commercial films, coded "YELLOW" and "NEUTRAL" according to their color, and an experimental film coded "BASF", as it was provided by BASF Italia SpA. The plastic films were tested on a seedless grapevine variety (Vitis vinifera 'Sublima Seedless') grown with three different irrigation treatments, i.e. V1, V2 and V3 corresponding to 100, 80 and 50% of the estimated vine evapotranspiration. Radiometric tests were carried out in laboratory on the plastic films at the beginning and at the end of the vegetation period. In the field, environmental parameters, such as photosynthetic photon flux, air temperature and relative humidity, were recorded. Vine water status and leaf gas exchange were measured during berry growth. At harvest, the vine productivity and the grape quality were assessed. At the beginning of the growing season the plastic films were characterized by PAR total transmissivity coefficient equal to 86.3% for the BASF film and 86.0% for YELLOW films; this coefficient was lower for NEUTRAL film (81.8%). Concerning the solar IR transmissivity coefficient, the YELLOW film was characterized by the highest value (90.0%), while BASF film by the lowest one (81.0%). Vines that received the lowest irrigation volume showed the worst water status and the lowest rates of leaf gas exchange, as expected; moreover, they limited their leaf area expansion. Leaves of vines under NEUTRAL film showed a tendency for a higher stomatal conductance and leaf transpiration, but not for a higher photosynthetic rate. The cluster weight was reduced on vines that received the lowest irrigation volume, while the berry reached the highest sugar content. The skin color parameters (L∗, a∗, b∗) were influenced by the different irrigation treatments and the different covering plastic films.