Effect of foliar application of urea and nano-urea on the cell wall of Monastrell grape skins

The foliar application of urea has been shown to be able to satisfy the specific nutritional needs of the vine as well as to increase the nitrogen composition of the must. On the other hand, the use of nanotechnology could be of great interest in viticulture as it would help to slow down the release of urea and protect it against possible degradation. Several studies indicate that cell wall synthesis and remodeling are affected by nitrogen availability.

The study was carried out over three years (2019, 2020 and 2021), the effect on the main components of the cell wall of Monastrell grape skins was compared to control after foliar treatments with urea and nano-urea. The treatments, in triplicate, were manually applied with a spray dispenser.

The proportion of isolated cell wall was increased in both treatments every year. This rise would indicate a thickening of the cell walls. Proteins were enhanced in 2019 and 2021 in grapes from the two treatments, whereas in 2020 they were not modified. Phenolic compounds were not affected in 2019, decreasing in the nano-urea treatment in 2020 and in the urea treatment in 2021. Cellulose was diminished in 2019 in the nano-urea treatment and in both treatments in 2021, but was not affected in 2020. Hemicellulose was increased for both treatments in both 2019 and 2021, but only for urea in 2020. Finally, uronic acids were lower compared to control for both treatments in 2019, but raise in the two subsequent years.

In conclusion, the cell wall was modified by both treatments, which may have implications on its rigidity and therefore on the extraction of the compounds of interest present in the grape skins. The treatments applied in the form of nano-urea had comparable effects to those obtained with urea in the conventional way, despite being applied at a significantly lower dose.

Acknowledgements: To all the staff of Estación Enológica de Jumilla