|AFIFI, MAHA - California Table Grape Commission|
|Obenland, David - Dave|
|EL-KEREAMY, ASHRAF - University Of California|
Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/30/2021
Publication Date: 8/18/2021
Citation: Afifi, M., Obenland, D.M., El-kereamy, A. 2021. The complexity of modulating anthocyanin biosynthesis pathway by deficit irrigation in table grapes. Frontiers in Plant Science. 12. Article 713277. https://doi.org/10.3389/fpls.2021.713277.
Interpretive Summary: Deficit irrigation is a common practice to improve the coloration of table grapes but sometimes the results are not satisfactory, particularly under very hot growing conditions. In this two-year study deficit irrigation was applied to table grapes in the Coachella Valley (high temperatures night and day) and in the San Joaquin Valley (more moderate temperatures) and the development of coloration and changes in plant regulatory factors studied. In both locations deficit irrigation induced the development of anthocyanins, pigments in the grapes responsible for the expression of color, although in the Coachella Valley there was less anthocyanin development. This difference in the response of the two locations was found to be tied to a lesser expression of genes involved in anthocyanin synthesis and an alteration in related plant hormone content. In addition, an impairment in antioxidant activity in table grapes from the Coachella Valley may also be involved. These findings indicate that deficit irrigation is an effective process in enhancing the color of table grapes but that under adverse environmental conditions, such as in the Coachella Valley, additional actions in the vineyard may be needed to achieve full coloration. These actions may include treatments to enhance light interception, hormonal balance, or antioxidant activities.
Technical Abstract: Deficit irrigation (DI) is one of the cultural practices that has been used to improve grape coloration, however, the result is not always satisfactory. Weather conditions, especially temperature, plays a crucial role in regulating anthocyanin pathway and it can play a role in the success of the DI technique. In the present study, we attempted to investigate the anthocyanin biosynthesis in ‘Scarlet Royal’ table grapes grown under two climate conditions in California (San Joaquin and Coachella valleys) and subjected to different deficit irrigation strategies. Our goal was to identify potential regulatory factors that might lead to applied treatments to be used in improving red color in grapes, especially under warm climate conditions. In both locations, deficit irrigation at veraison induced anthocyanin accumulation and enhanced red color in berries at harvest time. However, anthocyanin accumulation was lower under the warmer condition of the Coachella Valley compared to the San Joaquin Valley. The lower level of anthocyanin was associated with lower level of the expression of key genes involved in anthocyanin biosynthesis such as flavonoid-3-O-glucosyltransferase (UFGT) and myb-related regulatory gene (MYBA1). Gene expression analysis revealed the association of ABA biosynthesis gene 9-cis-epoxycarotenoid dioxygenase (NCED1), 1 aminocyclopropane-1-carboxylic acid oxidase (ACO3), a major gene in ethylene biosynthesis, and the gibberellic acid (GA) catabolic gene GA2 oxidase in the induction of anthocyanin biosynthesis. An increase in the chalcone synthase gene (CHS2) was observed in response to deficit irrigation treatments in both sites; however, its expression was higher in Coachella Valley after ending the deficit treatment, suggesting the involvement of the environmental stress in elevating the level of the CHS2 transcripts. Coachella Valley is characterized by high temperatures during the day and night in contrast to the less extreme temperatures of the San Joaquin Valley. This data was also supported by the fact that antioxidant gene expression and enzyme activities showed a lower level in the Coachella Valley compared to the San Joaquin Valley. The present data suggested that the lack of red coloration could be at least partially due to the lower level of the antioxidant activities resulting in accelerated anthocyanin degradation and impaired anthocyanin biosynthesis. It seems that under challenging warmer conditions several factors are required to optimize anthocyanin accumulation by deficit irrigation, including an active antioxidant system, proper light perception and hormonal balance.