Maha Afifi,* David Obenland, and Ashraf El-kereamy
*California Table Grape Commission, W Fallbrook Ave, Fresno, CA 93711 (maha@grapesfromcalifornia.com)

Deficit irrigation (DI) is an irrigation scheduling technique used to improve red color development in grapes. The red color in grapes is mainly due to the plant pigment anthocyanin.  Anthocyanin biosynthesis was investigated in Scarlet Royal grapes, grown in the San Joaquin and Coachella valleys and subjected to two different deficit irrigation strategies. Total berry skin anthocyanin contents and the individual pigment compounds increased with DI at both experimental sites. DI induced expression of several genes involved in anthocyanin accumulation. Expression analysis of genes involved in anthocyanin biosynthesis revealed the induction of key genes such as UDP-glucose: flavonoid-3-O-glucosyltransferase (UFGT) following DI. However, the expression of this gene was lower in Coachella Valley than in San Joaquin Valley. Data also showed an increase in the expression of chalcone synthase gene (CHS2) in response to DI treatments at both sites; however, the expression of this gene was higher in Coachella Valley, after ending the deficit treatment and re-irrigating the vines. This gene is well known to be involved in response to different stress conditions, besides its role in anthocyanin biosynthesis. Thus, the high expression of this gene in the Coachella Valley could be due to the induction by other environmental stress conditions. This data was supported by the fact that antioxidant genes expression showed a lower level in the Coachella Valley. Together, these findings suggest that the lack of red coloration in the Coachella Valley could be due partially to less antioxidant activity. The low level of the antioxidant activity allows the accumulation of free radicals, resulting in impairing anthocyanin biosynthesis.

Funding Support: California Table Grape Commission