Colored hail‐nets as a tool to improve vine water status: effects on leaf gas exchange and berry quality in Italia table grape

Abstract

Context and purpose of the study ‐ Protecting table grape vineyards with white hail‐nets is a common practice in Southern Italy. Hail‐nets result in shading effects of 10‐20 %, depending on their density and type of weave, thus they act as a low shading nets and modify the vineyard microclimate. Darker nets are more opaque to solar radiation, increasing the shading effects. Colored nets have been introduced in horticultural crops aiming to alter the amount and composition of light available at canopy level, in order to getparticular light‐induced effects on microclimate, plant physiology, growth and production. Yellow and red nets are among the most studied. However, by now, results of different studies are not always consistent with each other. The present study aimed at assessing the performance of Italia table grape grapevine under yellow and red hail‐nets, with a particular interest to the chance of modulating the microenvironment to support the vine water status under the semi‐arid conditions of Southern Italy, evaluating also the effects exerted on the grape quality.

Material and methods ‐ The study was run in 2014 and 2015, in the BT province of Apulia region, on Italia covered with white, yellow and red nets, all having mesh of about 3×5 mm. PAR, air temperature and RH were monitored in warm hours of typical days of mid‐ and late‐ July and August. Leaf gas exchange and stem water potentials were measured. Leaf area was assessed ceptometrically. At harvest, berry fresh weight, skin color, juice total soluble solid concentration (TSS) and titratable acidity (TA), main skin and pulp phenol contents, and berry antioxidant activity (AA) were determined.

Results – Respect to the white net,the colored ones reduced the PAR available for canopy (especially the red net) and increased air temperature and RH (especially the yellow net). On average, they lowered the air VPD along the canopy profile by ~10% and improved the vine water status from 33 % (yellow net) to 38 % (red net). However, this improvement did not enhance the leaf gas exchange measured at maximum PAR 2 interception (~1450 ~mol/m /s); on the contrary, the leaf transpiration, and even more the net CO2 uptake, tent to be lowered by yellow net, but not, or at a little extent, by the red net. The leaf area did not change. According to literature, yellow color depresses the transmissivity of red and blue wavelengths, active on photoreceptors that stimulate stomata opening and PSII efficiency. At harvest, on average, the patterns of berry and bunch weight were similar to those of leaf gas exchange (especially to the transpiration one); the yellow component of the skin color decreased with both colored nets; the TSS/TA ratio increased. The skin phenol contents were lowered by the red net but not, or a very little extent, by the yellow one; the berry antioxidant activity progressively decreased passing from the white to the yellow and to the red net. In conclusion, under the trial conditions, the yellow and red hail‐nets did not influence the performance of Italia grapevine in univocal way. Some responses seemed more related to their low shading effects, while others to their spectrometric effects. They rose significantly the vine water status compared to the white net, but this improvement did not enhance other physiological parameters or any berry quality attributes.