Frequently, in warm climates such as Mediterranean areas, a red-pink table grape ‘Crimson Seedless’ does not reach a good berry skin color; and an acceptable anthocyanin bioactive compounds content, responsible for the red color of berries. Harpin proteins are biotechnologically developed bio-activators that, if applied on plants during the growing period, trigger the expression of hundreds of genes among which those associated with the biosynthesis of bioactive compounds (such as anthocyanins).

This research aimed at using harpin proteins to test their suitability in improving the grape skin color.

Beta-harpin protein 1% p.a. (400 g/Ha) was applied to ‘Crimson Seedless’ vines three times at the beginning of veraison. Six samplings were carried out for both the treated and control grapes until commercial harvest. In the skin extracts, total and individual anthocyanins content was determined by UV-Vis and RP-HPLC-DAD analyses, respectively.

The collected results confirmed that the application of harpin proteins effectively stimulated the anthocyanin biosynthesis leading to make peonidin-3O-glucoside, cyanidin-3O-glucoside, and malvidin-3O-glucoside values from 2 to almost 10 folds higher in treated grapes than in control grapes (P < 0.05).

Actually, harpin proteins improved the color of the berry skin, leading to a significantly higher concentration of anthocyanins in treated than in control grapes.