|ISMAIL, AHMED - University Of California
|PARVEZ, TARIQ - University Of California
|REZK, ALAAELDIN - University Of California
|COMSTOCK, STACEY - University Of California
|VIDALAKIS, GEORGIOS - University Of California
|BODAGHI, SOHRAB - University Of California
|EL-SHARKAWY, ISLAM - Florida A & M University
|Obenland, David - Dave
|EL-KEREAMY, ASHRAF - University Of California
Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2023
Publication Date: 10/26/2023
Citation: Ismail, A., Parvez, T., Rezk, A., Comstock, S., Vidalakis, G., Bodaghi, S., El-Sharkawy, I., Obenland, D.M., El-Kereamy, A. 2023. Unraveling the occasional occurrence of berry astringency in table grape cv. Scarlet Royal: A physiological and transcriptomic analysis. Frontiers in Plant Science. 14:1271251. https://doi.org/10.3389/fpls.2023.1271251.
Interpretive Summary: The table grape variety Scarlet Royal is a very popular grape grown in California that is much appreciated by consumers. Occasionally it is observed that the grapes of this variety can be astringent which greatly damages the eating quality by imparting an unpleasant drying sensation in the mouth. Why this occurs is poorly understood. In this study one field location (V7) was sampled where grapes did not develop astringency and another (V9) where it was known to occur. Analysis of various components of the grapes indicated that the location V9 had much greater levels of tannins, which have been previously shown to cause astringency, after late grape development. This corresponded to higher levels of gene expression of enzymes key to the synthesis of tannins in the grapes from location V9. It was also observed that astringency was also related to poor coloration of the grapes. This study gives information useful in the determination of how to prevent or minimize astringency in the variety Scarlet Royal.
Technical Abstract: Scarlet Royal, a mid-season ripening table grape, is one of the popular red table grape varieties in California. Occasionally and under certain circumstances, an undesirable astringent taste has been observed in this variety. In fact, several factors may contribute to the degradation of berry attributes, including the development of an undesirable taste. Of significant importance, the levels and compositions of polyphenols that define berry quality and sensory characteristics. The current study was designed to understand this phenomenon by comparing Scarlet Royal berries from two contrasting vineyards. Berries from the V7 location exhibited well-colored and non-stringent characteristics, whereas those from the V9 vineyard showed the opposite. The data revealed that the divergence in berry astringency stemmed from alterations in its polyphenol composition, most notably tannins, during the late ripening stage at the V9 vineyard. Through our research, we were able to determine that the threshold level of tannins causing the Scarlet Royal astringency taste is around 400 mg/L. Transcriptomic profiling of berries positively linked the flavonoid/proanthocyanidins (PAs) structural genes with the accumulation of PAs in V9 berries, subsequently leading to the development of astringency taste on one hand, and low red color intensity on the other hand.