Ashraf El-kereamy,* Ahmed Ismail, Tariq Tariq, Alaaeldin Rezk, and David Obenland
*University of California Riverside, 900 University Ave, Riverside, CA, 92521 (ashrafe@ucr.edu)

Scarlet Royal, a mid-season ripening table grape, is a popular red grape variety in California. However, its berries develop an undesirable astringent taste under certain conditions. A series of trials have been conducted to comprehend the underlying mechanism and control of astringency development. First, we used total phenolic analysis to determine the components responsible for the astringent taste. Second, we identified the pathway involved in this process. By comparing Scarlet Royal berries with non-astringent varieties, we determined the threshold of tannin levels that cause the berry’s astringent taste. Our data showed that berry astringency is correlated with high petiole nitrogen levels and can be managed through N fertilization. Additionally, our data showed that a lower cluster number per vine could contribute to the induction of berry astringency. Further, berry astringency is associated with late harvest dates after the middle of September; however, it is not associated with high sugar content, as some people believe. It was associated with a lower level of anthocyanin in the berries at harvest. Table grapegrowers could control the induction of berry astringency in Scarlet Royal table grape by monitoring and maintaining a reasonable N level during flowering and berry development, and by not reducing the cluster number to 20 clusters per vine.

Funding Support: California Table Grape Commission