Anthocyanin variation in individual 'Shiraz' berries as affected by exposure and position on the rachis

This study was done on 'Shiraz'/Richter 99 grapes with the intention to define the variation of skin anthocyanin content in a single berry. The effects of berry position (on the rachis), berry exposure, berry weight category, part of the skin of a single berry, and their interactions, were analysed. The anthocyanin concentration of externally facing berries decreased and that of the internally facing berries increased from the apical part to the basal part of the bunch. Highest values were recorded in internally facing berries and lowest values in the externally facing (exposed) berries, of the basal rachis area. Anthocyanin values of small berries seemed to decrease from the apical part of the rachis to the basal part, whereas those of the larger berries generally increased. Anthocyanin distribution in the skin of a single berry was similar for all the berry weight categories. The median concentric layer of the berry showed the highest anthocyanin concentration. The study showed significant intra-berry variation, indicating that even at full ripeness stage there is still variation in every single smaller or larger berry. The results highlighted the very complicated management challenges to grape producers to increase bunch uniformity in quantity and quality.