Studies on the coloration of grapes. VI.

Effects of shading on the coloration and pigmentation of Muscat Bailey A (black grapes)

Abstract

1. This experiment was conducted in 1964 to observe the effects of shading on the berry coloration and pigmentation of Muscat Bailey A grapes (black variety). Each cluster was enclosed with either kind of bags made of alminium foil or cheese cloth, receiving only 0 or 25% of natural light intensity respectively. Shading was done at the different stages of berry development of (I) June 4 to July 7 (stage of rapid growth), (II) July 7 to August 5 (stage of depressed growth), (III) August 5 to September 7 (stage of final swell), (IV) June 4 to August 5(I+II), (V) July 7 to September 7 (II+III) and (VI) June 4 to September 7 (I+II+III).
2. Complete shading of clusters at the stage of rapid growth reduced greatly the yield of berries, so that it improved somewhat the coloring of the remained berries, increasing both the contents of the anthocyanins in the skin and the reducing sugars in the juice. Shading at the stage of depressed growth gave only a slight bad effect on the berry color. However, shading at the stage of final swell depressed markedly the berry color, lowering both the contents of the anthocyanins and the reducing sugars remarkably.
3. As berries formed the anthocyanins in their skin even when shaded throughout their growing seasons, the 25% treatment was not so effective as the 0% treatment. The content of anthocyanins correlated highly with the color degree of berries and the content of reducing sugars. In the result of the photodensitometric measurement, seven kinds of anthocyanins were isolated, but their qualitative differences seemed to be not so important as their total amount for the color development of berries.