Carry over effect of shoot trimming and deficit irrigation on fruit yield and berry total soluble solids

Abstract

Context and purpose of the study – The increase in air temperature that is occurring in many important wine-growing areas around the world is resulting in the decoupling between the phenolic and the technological maturity of grapevine berries. This new ripening pattern leads to the production of light-bodied high alcoholic wines, but this is in countertendency with the increasing consumers’ demand for wines with low-to-mid alcohol concentrations. The oenological techniques proposed to reduce wine alcohol content are often very expensive and lead to detrimental effects on wine quality. Many viticultural practices have been proposed to slow down sugar accumulation the berry. One possible strategy that was previously found to be suitable for Aglianico grapevine is post-veraison shoot trimming. The aim of this work was to assess the carry over effects on the following year of shoot trimming and vine water status on yield and total soluble solids because the expected reduction in vine fertility could lead to a reduction in the effectiveness of shoot trimming. 

Material and methods – The trial was carried out over four years (from 2017 to 2020) in a commercial vineyard located in Mirabella Eclano (Avellino, Italy). Vines were 13-year-old Aglianico grapevines (Vitis vinifera L.) grafted onto K5BB, spaced 2.5 × 1.0 m, trained to a bilateral spur cordon with a N-S row orientation. The experimental design was a randomized complete block design with nine treatments and four blocks; The treatments resulted from the combination of three levels of shoot trimming with three different irrigation strategies applied when the total soluble solids (TSS) were 12 °Brix. Shoot trimming treatments consisted in the removal of 30% and 60% of leaf area (respectively T30 and T60) and a untrimmed control (T0), whereas irrigation treatments replaced 0%, 50% or 100% of Etc (I0, I50, and I100, respectively). The harvest was performed when all the treatments reached phenolic maturity and yield and berry composition were measured.

Results – The results showed how severe shoot trimming can lead to a reduction in vine yield in the following years. This effect was manifested starting from the second year of the trial in rainfed vines exposed to severe trimmed, whereas this effect appeared later in irrigated and severely trimmed vines (3^rd year of experiment). We found a negative relationship between yield and the intensity of water stress in the previous year, but this relationship is affected by the intensity of shoot trimming applied. However, yield reduction did not cause an increase in TSS as compensating effect in T60 vines. Severe shoot trimming reduced TSS content each year but the effect was found to be greater for dryer years. Mild shoot trimming conversely increased TSS in berry juice in particular during mild seasons.