Impact of light exposure on fruit composition of white 'Riesling ' grape berries (Vitis vinifera L.)

Microclimate and irradiation have long been known to influence winegrape (Vitis vinifera) quality. However, microclimate influence on white grape qual-ity has remained understudied, as most research efforts have focused on red varieties and their anthocyanin content. In this study, we investigated microclimatic effects on the phenolic and amino acid composition of white 'Riesling ' grapes using bunch shading and leaf removal to manipulate grape microclimate. Both treat-ments were applied directly after fruit set (modified E-L 27; (COOMBE 1995)) as well as at the onset of verai-son (E-L 34), and compared to a non-manipulated con-trol. The concentration of malic acid, amino acids and total nitrogen were decreased by illumination during the berry growth, while content and concentration of phenolics were significantly increased by illumination. Strong negative correlations were observed between accumulation of amino acids and flavonols. Although accumulation of flavonols occurred throughout berry development, the most important phase of accumula-tion was post-veraison. K e y w o r d s: Berry composition; leaf removal; light exposure; phenolics