Water and physiological response to early leaf removal of cv. Verdejo in rainfed conditions, at different times of the day, in the D.O. Rueda (Spain)

Aim: Early leaf removal, generally applied before flowering, is mostly conceived as a technique to control grape yield and improve the health of grapes and focused on the final objective of increasing wine quality.

New knowledge of its possible physiological effects in the cv. Verdejo, in rainfed conditions, should facilitate the understanding of agronomic, vegetative and qualitative behaviour of the vineyard, thus generating more possibilities of adaptation to optimize the grape ripening process.

Methods and Results: Leaf removal was carried out by removing the first eight adult leaves, from the base, on all shoots. The trial was carried out with cv. Verdejo, grafted onto 110R, planted in 2006 and trained on a vertical trellis, in rainfed conditions, in the D.O. Rueda.Throughout the period of 2016-2018, the physiological response of the vines to early leaf removal (before flowering) was studied through measurements of water potential at 7, 9, 11 and 12 hours (solar time) and stomatal conductance, transpiration and net photosynthesis at 9 and 12 hs.

The water potential measured at different times of the day showed no differences between treatments. The values were slightly higher in the control vines sometimes and higher in the leaf plucked vines other times, but more frequently favourable to the control vines in 2017 and 2018, especially in the measurements at 9 and 11 hs. Gas exchange (Gs, E, An) also did not show statistically significant differences between treatments. Some values were slightly favourable to the leaf removal treatment, such as at 9 hs in 2016, and other values were slightly favourable to the control treatment, such as at 12 hs in 2017 and at 9 hs in 2018.

Conclusions:

The results observed in the water potential and in the gas exchange at different times of the day have not generally discriminated between the leaf removal applied at the beginning of flowering and the control treatments.

Significance and Impact of the Study: The agronomic benefit intended with the early leaf removal, generally to lighten the compactness and weight of the bunch, as well as its aeration and luminosity, does not have to be questioned from the water or physiological point of view in the cv. Verdejo on rainfed conditions.