The Effect of Foliar Application of Ascorbic Acid and Oxalic Acid on the Physiological Responses of Strawberry cv. Camarosa

Introduction In recent years, the use of organic acids has increased due to their role in the quantitative and qualitative yield and resistance to environmental stresses. Ascorbic acid (vitamin C) is one of the important antioxidants and plays a role as the primary substrate in cyclic pathways to remove toxicity and neutralize superoxide and single oxygen radicals. Ascorbate is also involved in the regulation of cell division and photosynthesis and has nutritional value for humans and is probably important for the tolerance of plants against photo-oxidative stress. Oxalic acid is a metabolic end product in plants that has many physiological functions, the main ones is the induction of resistance to disease and environmental stress by increasing the activity of enzymes involved in resistance and secondary metabolites such as phenol, flavonoid, etc. Considering the importance of the physiological traits of the plant in the production of quantitative and qualitative yield of strawberry and on the other hand, the lack of sufficient information about the effect of external application of ascorbic acid and oxalic acid on the physiological traits of the plant, the present research work aimed to investigate some physiological and qualitative traits of strawberry leaves and fruits affected by foliar spraying of ascorbic acid and oxalic acid.   Materials and Methods The experiment was conducted based on randomized complete block design (RCBD) with three replications in Darkalate village of Ramiyan city of Golestan province to investigate some physiological responses of strawberry cv. Camarosa to the foliar application of organic acids. The experimental treatments consisted of three levels: non-spraying as control, spraying with 1 mM ascorbic acid and 1 mM oxalic acid, which was performed in three stages (from end flowering stage to the green fruit stage) at 6 days intervals. Finally, three plants were selected from each experimental unit and leaf samples were taken and transferred to the laboratory to measure physiological traits i.e. leaf area, fresh and dry weights, total chlorophylls, chlorophyll a and chlorophyll b, total carotenoids, total sugars, total phenols and flavonoids. Also, when at least 75 percent of the fruit surface turned red, the fruits were harvested from each plot separately and immediately transferred to the Plant Physiology Laboratory of Gorgan University of Agricultural Sciences and Natural Resources. The physicochemical traits of strawberry fruits including total soluble solids (TSS), titratable acidity (TA), flavor index, vitamin C, total phenol, flavonoid, antioxidant activity, total anthocyanins were measured. Analysis of data were performed using SAS 9.2 statistical software and comparison of mean data were undertaken based on LSD statistical test.   Results and discussion The results showed that the foliar application of ascorbic acid and organic acid had a significant effect on the leaf area, fresh and dry weights, total chlorophylls, chlorophyll a, chlorophyll b, carotenoids, total sugars, phenols and flavonoids. The highest mean leaf area (314.08 cm2), leaf fresh and dry weights (1.78 and 0.56 grams, respectively), chlorophyll a (0.43 mg/g), total carotenoids (0.29 mg/g), total sugars (1.43 µg/g), total phenols (0.70 mg/g) and flavonoids (0.19 mg/g) were observed in the application of oxalic acid. The control had the lowest mean in all studied traits (except carotenoids). The application of both ascorbic acid and oxalic acid resulted in an increase in photosynthetic pigments, elevating the total chlorophyll content by an average of 22% compared to the control group. Additionally, foliar spraying with ascorbic and oxalic acid led to higher levels of total soluble solids, increased antioxidant activity, and enhanced total flavonoid content in the fruit compared to the control group.Moreover, fruits harvested from plants treated with oxalic acid before harvest exhibited higher levels of total anthocyanin and phenol compared to fruits from plants treated with ascorbic acid before harvest and the control group. Fruits of plants treated with ascorbic acid compared to plants treated with oxalic acid had lower vitamin C and titratable acidity and higher flavor index. The physiological influence of oxalic acid was more superior than that of ascorbic acid and had higher positive effects in the studied traits were recorded. However, since ascorbate is one of the precursors of oxalic acid biosynthesis. Therefore, the changes caused by oxalic acid are indirectly influenced by ascorbic acid. Ascorbic acid acts as a cofactor in photosynthetic reactions and prevents the destruction of chlorophylls and carotenoids due to its antioxidant property, and by interfering in cell division and increasing the surface area of leaves; it increases photosynthesis and the production of carbohydrates. In general, according to the results, it was found that the application of ascorbic acid and oxalic acid improved the quality characteristics and the content of health related compounds of Camarosa strawberry fruit by increasing photosynthetic pigments and biomass.