ffect of Foliar Application of Zinc and Boron on Quantitative and Qualitative Characteristics of Strawberry Fruit (Fragaria ananassa cv. Aromas) in Hydroponic System

Strawberry (Fragaria × ananassaDuch.,Rosaceae). fruitis rich of fiber, vitamin C, potassium and antioxidants. Since the balance of nutrients at the appropriate time for commercial fruit production, yield improvement and fruit quality is essential, so foliar application at key stages could have a positive effect on the quantitative and qualitative characteristics of perennial crop fruits. Among essential mineral nutrients that are involved on plant physiology, micronutrients of zinc (Zn) and boron (B) because of their association with synthetic hormones are particularly important. In a study by Lolaei et al. (2012) conducted showed that the foliar application at flowering stage increased fruit quality and yield of strawberrycultivar ʻCamarosa’. The results of Rafeii and Pakkish(2014) indicated that spraying of strawberry cultivar ʻCamarosa’ with boric acid had a significant effect on yield, fruit weight, chlorophyll and leaf area. So according to the importance of micronutrients on horticultural yield improving and environmental protection, this investigation was conducted to evaluate the effect of foliar application of zinc and boron and combination of them on quantitative and qualitative characteristics of strawberry cultivar ʻAromas’ in hydroponic system.
Material and The experiment was arranged in factorial based on a complete randomized block design with 9 treatments and 9 replications in 2015 and 2016 in greenhouse and laboratory of Genetics and Agricultural Biotechnology Institute of Tabarestan (GABIT), Sari Agricultural Sciences and Natural Resources University, Sari, Iran. Experimental treatments were included: zinc at three levels (0, 100 and 200 mg l-1) of fertilizer source zinc sulfate and boron at three levels (0, 500 and 1000 mg l-1) of fertilizer source boric acid as alone or combined. Spraying of strawberry cultivar ʻAromas’ at 3 stages in hydroponic system were applied after the chilling requirement treatment. When Fruits were stained 75-80% and have appropriate size, were harvested. Traits that were evaluated include: vitamin C, antioxidant activity, total soluble solids (TSS), titratable acidity (TA), taste index (TSS/TA), pH of fruit juice, chlorophyll a, chlorophyll b, carotenoid, fruit weight, fruit length and diameter, leaf number, petiole length and plant height. The data collected were statistically analyzed using the computer software using SAS 9.1 and MSTATC, Analysis of variance techniques were employed to test the overall significance of the data, while the least significant difference (LSD) test (P ≤ 0.05) was used to compare the treatment means. Results indicated that foliar application of Zn and B significantly affected on the vitamin C, antioxidant activity, TSS, TA, TSS/TA, pH of fruit juice, chlorophyll a, chlorophyll b, carotenoid, fruit weight, fruit length and diameter, leaf number and plant height (1% or 5% of probably level), while the Petiole length was not significantly affected. Between the different nutrient levels of zinc sulfate application at the concentrations of 100 and 200 mg l-1, boric acid application at the concentration of 500 mg l-1, the combination of zinc sulfate at 100 and 200 mg l-1 with boric acid at 500 mg l-1 play a significant role at increasing studying characteristicsexcept the content of TA. Zinc is effective at the formation of growth hormones and chloroplasts, it is also necessary for chlorophyll biosynthesis and also plays a very important role at cell division and the protein synthesis and carbohydrates metabolism. It seems this subject caused increased plant height, leaf number, petiole length, diameter, length and weight of the fruit and chlorophyll by foliar application. Boron is an element which increases weight by effect of reproductive growth and help to material production, production and transfer of carbohydrate, and nutrient by boron is necessary for fruit set and fruit retention. The results showed that zinc sulfate is effective on TSS, TA, taste index and pH, the increase may be attributed to their effects on different enzymes which are involved in the formation of proteins, acids and sugars, also enough amounts of boron in the plant, increased carbohydrate transport to fruit and areas of active growth and its effect is evident in increasing the amount of fruit sugar. Because of increased vitamin C and antioxidant capacity of plants had been sprayed with boron and zinc can be attributed to zinc that plays an active role in auxin production in plants, and vitamin C increases the production of auxin. Similarly, Kazemi (2014) reported the highest pH of fruit juice, TSS and TA at 150 mg l-1 of Zn for strawberry cultivar ʻPajaro’ and the lowest of these parameters was recorded in control. The results of our study is in accordance with Mashayekhi and Atashi(2012) who reported a significant positive correlation between chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid content of strawberry cultivar ʻCamarosa’ leaves that had been sprayed by B and sucrose. As Khan et al. (2015) simultaneously combined application of Zn and B in the ʻKinnow’ mandarin fruit increased vitamin C, tree height and fruit weight, diameter and length significantly that was consistent with our results. Since the foliar application of zinc sulfate at 100 and 200 mg l-1 with boric acid at 500 mg l-1 showed significant effect on quantitative and qualitative properties of strawberry, so to reduce the environmental effects caused by the indiscriminate use of chemical fertilizers, foliar application of micronutrients is recommended as an effective management solution in the production of strawberry cultivar ʻAromas’ under hydroponic culture.