The Effect of Foliar Spray of different Calcium Sources on Antioxidant Properties and Quality of Cauliflower (Brassica oleracea cv. botrytis ‘Romanesco’)

Introduction  Cauliflower is one of the world’s most important vegetable crops. The edible head of the cauliflower is called curd, which is composed of many florets formed of aborted floral meristems. Curd has various components with high nutritional value including glucosinolates, vitamin A and C, phenolic compounds, and carotenoids, which exert beneficial effects on our health. Calcium is an essential macronutrient that plays a vital role in maintains cell wall stability, integrity and determining the fruit quality. Several researches have explored the effects of calcium salts on plant growth and quality in many horticulture crops. Various studies indicate that Ca2+ reduced peroxidation of lipid, increased activity of antioxidant enzyme and improve osmotic adjustment of cell membranes. Plant roots absorb calcium from the soil solution in the form of Ca2+ ions. The mobility of calcium in plant is low, and the root uptake from fertilized soils is poorly effective in increasing the calcium content in leaves and fruits. Deficiency of Ca will appear in younger leaves and in fruits, due to its low rate of transpiration. Thence, it is necessary to have a constant supply of calcium to continue growing. The direct application of liquid source of calcium on leaves and fruits may offer an alternative solution. The efficiency of foliar application with Ca depends on the source of Ca and applied dosage. To our knowledge, however, little information is available regarding the effect of different calcium sources on cauliflower. Thus, the aim of this study was to investigate the effect of foliar spray of calcium sources on quality and antioxidant properties of cauliflower cv. Romansco. Material and Methods  In order to evaluate the effect of different sources of calcium on antioxidant properties and quality of cauliflower cv. Romansco, the field experiment was carried out as a randomized complete block design with three replication during 2018 at Research farm of faculty of Agriculture, at the University of Zanjan, Iran. Cauliflower plants (cv. Romanesco) were cultivated by applying conventional farming practice for growing in open air conditions. Different calcium sources including calcium nitrate (Ca(NO3)2, 0.5, 1 and 1.5 %), calcium chloride (CaCl2, 0.3, 0.6 and 0.9 %) and calcium lactate ( C6H10CaO6, 0.5, 1 and 1.5 g L-1) were sprayed in vegetative stage and 10 days after curd formation for 2 times onto the leaves and curd until runoff using a mechanical mist sprayer. Distilled water was used as a control. Potassium, phosphorus, total soluble content, titratable acidity, ascorbic acid content, total phenols and flavonoids, free radical scavenging activity (DPPH) were measured. Statistical analyses were performed with SPSS software package v. for Windows, and means comparison were separated by Duncan’s multiple range tests at p < 0.05. Results and Discussion  The results showed that foliar spray of different Ca sources significantly increased K content and decreased P content. The highest amount of K (5.6 µg mg-1DW) was achieved in CaCl 0.9% treatment. The highest value of flavonoids (0.86 and 0.85 %) was found in plants treated with CaL 1.5 g L-1 and CaCl 0.9%, respectively. In this study, also it was found that foliar spray of CaN 1.5% and CaCl 0.9% increased respectively 49.3 and 40.4% vitamin C content compared to control plants. Ca application with increasing phenolic compound and vitamin C contents, improved antioxidant capacity and the maximum antioxidant capacity (26.19%) was found in CaL 1.5 g L-1 and CaN 1.5% treatments. Application of Ca sources increased TA and TSS content. The highest TSS content (12.5 and 13.3 ºB) was achievd in CaCl 0.9% and CaL 1.5 g L-1 and the maximum TA (28.8%) was found in plant treated with CaCl 0.9%. In this regard, foliar application of high level of calcium sources was more efficient than of lower levels on cauliflower quality. Therefore, the leaf application of calcium can be effective in improving the quality of vegetables, especially cauliflower. Conclusion  Study results suggest that spraying different Ca source improved quality and antioxidant properties of cauliflower cv. Romanesco, so that with the application of Ca salts increase K, vitamin C, phenol and flavonoids contents. Among the calcium treatments used, higher levels of all three salts of CaCl, CaN and CaL had the most influence, so these calcium treatments are recommended to improve the quality and antioxidant properties of Romanesco cultivar.