Effects of abscisic acid (ABA) applications on color quality of table grapes - a meta analysis

The quality and value of colored table grapes are determined by the general appearance of the bunch, as well as the coloration and the amount of anthocyanins from phytochemicals. These criteria are important quality characteristics for consumers. Less color development and lower anthocyanin levels in colored grapes are due to various factors. In recent years, different external chemicals have been applied to grapevines to improve the pigmentation of the fruit. One of the most researched chemicals for this purpose is abscisic (ABA) acid. There is no consensus on the most appropriate ABA application time and dose to continuously improve the berry skin color and phytochemical content. The aim of this study was to evaluate the effects of ABA application on color parameters of fruits in colored table grapes by meta-analysis method. To achieve this aim, meta-analysis of 46 publications related to ABA in table grape varieties was reduced to 26 studies with 10 data editing steps. L, Croma (C*),CIRG (Color index of red grapes), hue (h0) and anthocyanin parameters in peel were taken into consideration in meta-analysis. In meta-analysis, values of control and most effective dose were used in articles. Effect Size Calculations (Cohen's d) was performed for the parameters related to the effect of ABA application on color quality and also correlation analysis was performed to understand the relationships between color parameters in the data set. According to the studies, forest plot was used to evaluate effect sizes and confidence intervals and Funnel plot was used to evaluate publication bias. In funnel plot, observations of the spread of studies, asymmetric distribution and potential publication bias were made. In the forest plot, the distribution of studies, the direction of effects, heterogeneity and detailed location and comments of the studies were made. Detailed comments were made on the articles that showed distribution at 3 different points as mean difference in the forest plot and location of the effect size line in the funnel plot. As a result of the activity analyzes, Forest plot and Funnel plot and T test; it was determined that ABA applications had a significant and positive effect on L*, Croma, h0, CIRG and anthocyanin values compared to the control. Meta-analysis shows that the application group significantly decreased L; Croma and, h0 values compared to the control group, and increased the amount of CIRG and anthocyanin. These effects were statistically confirmed by meta-analysis and paired t-test. The distribution of effect sizes and confidence intervals of the studies revealed significant heterogeneity among the studies. This indicates that the effect of the treatment varies across studies. These differences may be due to sample size, methodological differences, different ecologies and varieties in which the studies were conducted, or other study conditions. It is recommended that studies with larger sample sizes be conducted in the future.