The Effect of Abscisic Acid on Tomato Calcium Partitioning and Fruit Quality

Tomato (Solanum lycopersicum) is a widely employed plant model system for studying fruit metabolism, development and ripening. Various environmental stress factors, such as drought and high relative humidity, can cause calcium (Ca) deficiency and lead to physiological diseases such as blossom-end rot (BER) in tomato fruit. Recent studies demonstrate that abscisic acid (ABA) triggers whole-plant and fruit-specific mechanisms to increase fruit Ca uptake and prevent BER development. The objective of this study was to evaluate the effects of exogenous ABA applications during plant development on tomato carotenoid pigments, soluble sugars, organic acids, aromatic volatiles, carbohydrates, and mineral nutrient content in ripe fruit, and to assess the impacts of ABA applications on BER by evaluating how exogenous ABA will affect the distribution of Ca between the leaves and fruit. There were a series of three experiments that examined two types of tomato plants, micro tomato and a commercial tomato cultivar 'Mt. Fresh Plus'. ABA was exogenously applied to the foliar and/or root tissue. Leaves were harvested and analyzed for chlorophylls, carotenoids, and Ca concentrations. Fruit tissue was harvested at red ripe maturity and analyzed for yield, BER and fruit quality parameter, such as carotenoids, soluble sugars, organic acids and aroma volatiles. The results indicate that applications of ABA treatments to tomato plants decreased the partitioning of Ca into the leaves while increasing concentrations in the fruit tissue. ABA treatments, in combination with the Ca treatment of 180 mg⋅L^-1 (milligram per liter), decreased the incidence of BER. Further, ABA treatments decreased BER even in the presents of low Ca in the fertilizer solution. Results indicate that ABA treatments are most effective in the early stages of plant development. This study demonstrated that ABA is a viable treatment to significantly improve tomato fruit quality. Specifically, ABA treatments increased tomato fruit carotenoids and soluble sugar, while decreasing organic acid concentrations. However, ABA treatments had a detrimental effect on aroma volatile concentrations. ABA treatment applications in conjunction with low Ca treatments did not prove to be effective in improving tomato fruit quality. This study demonstrated that foliar spray ABA applications are more effective than root ABA applications.