The Effect of Foliar Application of Ascorbic Acid and Calcium Lactate on Growth, Yield and Fruit Quality of Sweet Pepper

  Sweet pepper (Capsicum annuum L.) is a worldwide used vegetable, which is an excellent source of ascorbic acid and has high antioxidant capacity against oxidative damage caused by free radicals. Ascorbic acid (AsA) is a water-soluble vitamin that plays a key physiological role in scavenging reactive oxygen species (ROS), and enzyme cofactor. In recent years, the application of exogenous AsA has received much attention for use as a biologically safe compound for postharvest quality maintenance of many horticulture crops. Calcium is an essential micronutrient that plays a vital role in maintains cell wall stability, integrity and determining the fruit quality. To our knowledge, however, little information is available regarding the effect of ascorbic acid and calcium lactate on pepper fruits. Thus, the aim of this study was to investigate the foliar application of ascorbic acid and calcium lactate on growth, yield and fruit quality of sweet peppers. To study the effect of foliar application of calcium lactate (Ca) and Ascorbic acid (AsA) on growth, yield and fruit quality of sweet pepper, the field experiment was carried out from June to September 2016 at Research farm of faculty of Agriculture, at the University of Zanjan, Iran. Pepper plants (cv. California Wonder) were cultivated by applying conventional farming practice for growing in open air conditions. 210 plants (30 plants for each treatment) were selected for uniform size and fruit load, and were sprayed three times (0, 15, 30 days after full bloom) with an aqueous solution containing different concentrations of Ca (0, 0.5, 1 and 1.5 g L-1) and AsA (100, 200 and 300 mg L-1). Each treatment was carried out with three replicates. Pepper fruit were harvested at commercial maturity stage, and transferred to the laboratory on the same day. Leaf area was recorded whit measurement leaf area (DELTA-T DEVICEC LTD, ENGLAND). After fruit harvested, plant length was measured. Fruit was weighted after harvest to determine mean fruit weight. The fruit number per plant and fruit yield per plant was measured to determine of total yield. The total yield expressed in kg ha–1. Flesh firmness was determined with penetrometer (model Mc Cormic FT 32), using an 8 mm penetrating tip. Results were expressed in kg cm-2. The pH values of solutions were monitored with pH meter. TSS was measured in the extract obtained from three fruit of each replicate with a digital refractometer Atago PR-101 (Atago Co., Ltd., Tokyo, Japan) at 20◦C. Total ascorbic acid content was expressed as mg per 100 g of juice. Antioxidant activity was measured using the free radical scavenging activity (DPPH) and calculated according to the following formula:  RSA%= 100(Ac-As)/Ac. Statistical analyses were performed with SPSS software package v. 20.0 for Windows, and means comparison were separated by Duncan’s multiple range tests at p < 0.05. The results showed that foliar application of AsA had significant effects on growth and fruit yield. The highest fruit yield (897.1 g plant-1) was achieved at 300 mg L-1 AsA that had no significant difference with 200 mg L-1 AsA. Foliar application of AsA markedly increased vitamin C content, and also the highest value of total soluble solid (5.7 °B) was recorded from 300 mg L-1 AsA. Ca had no significant effects on growth and fruit yield but significantly improved fruit firmness. The highest fruit firmness (2.13 and 2.16 kg cm-1) was obtained from 1 and 1.5 g L-1 Ca. The maximum antioxidant activity was achieved with application of 300 mg L-1 AsA and 1.5 g L-1 Ca. The fresh sweet peppers were an important source of ascorbic acid for human consumption. AsA significantly increased the amount of vitamin C in the plum and sweet pepper fruits. Foliar treatment of Ca increased vitamin C content. Increasing vitamin C content in fruits after treatment with Ca could be related to inhibiting action of calcium on the activities of ascorbic acid oxidase that use ascorbate as a substrate. The results indicated that treatment of Ca produced fruits with higher firmness compared to control and other treatments. Firmness and resistance to softening can be increased by the addition of Ca, due to interaction of calcium with pectate acid in the cell wall to form calcium pectate and retarding polygalacturonase activity. Differences in the percentage of TSS content at the time of harvest indicated the AsA and Ca effects on carbohydrate accumulation in fruits, which had different potential on respiration rates and consequently storability of plants. The exogenous application of AsA and Ca in sweet pepper plants indicated that treatments had significant effects on ascorbic acid content of sweet peppers. The antioxidant activity has positive correlation with total phenolic content, flavonoids and content of ascorbic acid. The results of our research indicated that per-harvest foliar application of AsA increased plant growth, fruit number and weight. Also, AsA and Ca treatments improved fruit quality attributes including vitamin C, fruit firmness, TSS and antioxidant activity. These results suggest that AsA and Ca treatments, especially AsA 300 mg L-1 and Ca 1.5 g L-1, may be proposed to improve fruit quality.