|Authors: ||M. Keller, N. Torres-Martinez|
|Keywords: ||Vitis vinifera, growth, gas exchange, fruit quality, phenolics, anthocyanins, flavonols, amino acids|
Ultraviolet (UV) radiation is known to influence plant growth, development, morphology, and physiology, but its effects on the fruit composition of grapevines are unknown.
Potted ‘Cabernet Sauvignon’ and ‘Chardonnay’ grapevines were grown in Australia under either ambient or reduced (2% of ambient) UV during two conescutive seasons.
UV reduction was achieved using diacetate films suspended above the plants.
In addition, two nitrogen treatments were applied at bloom in the first season and two water regimes were imposed from fruit set to leaf fall in the second season.
Ambient UV reduced early-season shoot growth but stimulated lateral shoot growth later in the season and enhanced root growth.
UV had no clear effect on leaf chlorophyll and gas exchange but reduced leaf water content and increased carotenoid and flavonoid concentrations.
Flower calyptra contained high concentrations of flavonols, but this UV protection was temporarily lost during cap fall (anthesis), making the flowers vulnerable to UV. The combination of ambient UV and low nitrogen stress resulted in reduced fruit set.
Nevertheless, UV failed to influence yield and fruit sugar content.
Ambient UV increased the flavonol content in ripening post-veraison berries, but had no effect on anthocyanins and hydroxy-cinnamic acids.
The impact of UV on fruit amino acids varied with individual compounds, but was insignificant for the predominant amino acids proline and arginine.
Hence, of the fruit composition parameters examined, only flavonols were notably affected by UV radiation.
Compared with ‘Chardonnay’, vegetative growth of ‘Cabernet Sauvignon’ was more tolerant, but reproductive growth was more sensitive to UV. In general, low nitrogen stress enhanced the UV effect, but low water stress reduced it.
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