ملیحه فرهنگ پور

Tomato (Solanum lycopersicum L.) belongs to the Solanaceae family, which is one of the most widely cultivated and economically important vegetables in the world, 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. Ascorbic acid is antioxidant and anti-stress agent, and also acts as a signaling molecule in some plant physiological processes and defense mechanisms. Positive roles of such antioxidants in scavenging or chelating the free radicals and activating the natural resistance against different biotic and abiotic stresses have been reported in several fruit trees. Calcium has a vital role for normal growth and development of plants due to an important role in balancing membrane structures, increasing nutrient uptakes and activates of metabolic processes. Calcium 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 interaction effect of ascorbic acid and calcium chloride on tomato. Thus, the aim of this study was to investigate the foliar application of ascorbic acid and calcium chloride on quality and antioxidant capacity of tomato fruit.

To study the effect of foliar application of calcium chloride (Ca) and Ascorbic acid (AsA) on growth, yield and fruit quality of tomato, the field experiment was carried out from June to September 2021 at Research farm of faculty of Agriculture, at the University of Zanjan, Iran. Each treatment was carried out with three replicates. Different concentrations of Ca (0, 0.3, 0.6 and 0.9 %) and AsA (0, 100, 200 and 300 mg.l-1) were sprayed three times (0, 15, 30 days after full bloom). Fruits were harvested at two harvests stage (orange and red color) and transferred to the laboratory on the same day. 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 fruit harvested at red color stage had higher vitamin C, total soluble solid (TSS), total phenol, flavonoids contents and antioxidant capacity compared to fruit harvested at orange color stage. Foliar application of AsA and Ca had significantly improved tomato fruit quality. The highest value of TSS (4.9 °B), vitamin C (46.1 mg.100 ml-1), total phenol and flavonoids contents and antioxidant capacity (36%) was achieved with application of 300 mg.l-1 AsA and 0.9% Ca in fruit harvested at red color harvest time. The lowest value of pH and highest TA was observed in red color fruit treated with 300 mg.l-1 AsA and all Ca levels. Ca had significant effect on fruit firmness, which the highest fruit firmness was obtained from 0.9% Ca. The fresh tomato is an important source of ascorbic acid for human consumption. AsA significantly increased the amount of vitamin C in the plum and sweet pepper fruits. 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 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 and Ca 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 0.9%, may be proposed to improve fruit quality.

Water stress is the most prominent abiotic stress limiting agricultural crop growth and productivity. Deficit irrigation stress as a consequence of the progressive decrease in water availability has been a hot topic regarding food security during the last two decades. Growth and development of plants are influenced by reduction in turgor that results in decreased nutrient acquisition from dry soil. Due to the threat of climate change, there is a need to limit the use of water resources in arid and semi-arid climates. It is therefore important to find new approaches to avoid crop productivity losses in ‘limited fresh-water’ areas. Eggplant (Solanum melongena) is an important non-climacteric fruit grown in tropical and subtropical regions. The estimated total world production for eggplants in 2019 was 51287210 tons. Foliar application of agro-chemicals has widely been used in agriculture as a rapid, low-cost and effective way for enhancing growth and productivity of many vegetable crops under water deficit conditions. Ca is an essential macronutrient for plant growth and development, and is considered as an important intracellular messenger, mediating responses to hormones, stress signals and a variety of developmental processes. Amino acids are important bio-regulators which have promotive effects on plant growth and productivity. Cysteine is the precursor molecule of glutathione, the predominant non-protein thiol, which plays an important role in plant stress responses.

The field experiment was carried out at the Research Farm of Agriculture Faculty, University of Zanjan, Iran, during 2021. The experiment was performed using a split plot based on a randomized complete blocks design with three irrigation regimes (60, 80 and 100 %ETc) as the main plot and foliar spray of two levels of calcium lactate (CaL) (1 and 2 g L-1) and L-cystein (Cys) (0.15 and 0.5 %) as the sub-plot in three replicates. Distilled water was used as a control. Eggplant (cv. Greta RZ) seedlings were transplanted at the 4-5 leaf stage with 35 cm spacing within row and 100 cm spacing between rows. After plant establishment, eggplants were sprayed with different concentrations of CaL and Cys at 6-7 leaf stage. Second and third times of foliar application were performed at 10 and 20 days after the first spraying. Irrigation treatments were applied one week after the first spraying. Number of branch per plant, plant height and leaf area were measured as growth parameters in harvest stage. Total chlorophyll and carotenoid contents, proline, leaf relative water content, stomatal conductance and electrolyte leakage were measured as physiological characteristics. Also plant fruit yield and water use efficiency (WUE) were evaluated.

As the results showed, plant growth, physiological indices and WUE significantly affected by deficit irrigation. Water deficit stress significantly reduced plant length, leaf area and chlorophyll content, and increased carotenoid content. Decreased plant growth may be due to limited cell division, cell enlargement due to turgor loss, and inhibition of various growth metabolites. Foliar spray of CaL and Cys improved plant growth, fruit yield and physiological indices. Leaf relative water content (LRWC) is among the main physiological criteria affecting plant water relations and have been used for assessing drought tolerance. Based on the findings, deficit irrigation caused a significant reduction in LRWC and stomatal conductance, which is due to the reduction of leaf water potential and the decrease of root water absorption rate under drought conditions. The highest value of LRWC and stomatal conductance were obtained in plants sprayed with CaL 2 g L-1 under irrigation 100 %ETc. Free proline is one of the most important osmolytes whose accumulation is a common physiological response to drought stress in higher plants and is probably associated with osmotic regulation and membrane stability under stress condition. WUE, the physiological parameter of crop, describes the relationship between plant water consumption and dry matter production. The proline content and WUE increased under deficit irrigation treatments; in particular with sever deficit irrigation (60 %ETc). The maximum proline content and WUE were observed in plants treated with CaL 2 g L-1 and Cys 0.5 % under deficit irrigation of 60 %ETc. The results showed that deficit irrigation led to a significant increase in electrolyte leakage compared to control, and foliar application of CaL and Cys decreased electrolyte leakage under normal and deficit irrigation conditions. Water deficit stress caused significant reductions in yield. The highest fruit yield was obtained under irrigation of 100 %ETc along with application of CaL 2 g L-1 and Cys 0.5 %.

Water deficit has been shown to adversely affect plant growth and fruit yield. Foliar application of CaL and Cys positively improved plant growth, physiological traits and fruit yield, as well as WUE. According to the results, application of CaL 2 g L-1 or Cys 0.5 % can be proposed to improve growth, fruit yield and WUE of eggplant.

In order to evaluate the effect of L-cysteine and calcium lactate on yield and fruit quality of eggplant (Solanum melongena cv. Greta RZ) under deficit irrigation, a split plot experiment based on randomized complete block design with three replications was conducted at Research Farm of University of Zanjan, during 2021. Experimental treatments were included three levels of irrigation (60, 80 and 100 ETc%) and five foliar spray treatments (two levels of calcium lactate (CaL) 1 and 2 g.l-1 and two levels of L-cysteine (Cys) 0.15 and 0.5%) and distilled water as a control. The results showed that deficit irrigation stress significantly affected plant yield and fruit quality. The lowest fruit number and plant yield (1.8 kg), sepal chlorophyll and vitamin C (11.65 mg.100ml-1) contents, and the highest phenols and flavonoids contents, electron leakage, and Antioxidant enzymes activity were obtained at deficit irrigation 60% ETc.  Foliar application of CaL and Cys significantly improved fruit yield and quality under normal and deficit irrigation. The maximum plant yield (4.4 and 3.9 kg), vitamin C content (44.1 and 41.9 mg.100ml-1) and total soluble solid content (4.4 and 3.9 °B) were found with application of CaL 2 g.l-1 and Cys 0.5% respectively under irrigation 100 ETc%. CaL and Cys with increasing antioxidant enzymes activity (superoxide dismutases, catalases and peroxidase) and phenolic compounds led to an increase in fruit antioxidant capacity. According to the results, application of CaL 2 g.l-1 and Cys 0.5% is recommended to improve yield and fruit quality of eggplant under normal and deficit irrigation condition.