The Effect of Ascorbic Acid on Vegetative Growth of Olive Plants cv. ‘Baghmalek’ under Water Deficit Conditions

Plant establishment is difficult in some arid and semi-arid regions of Iran because of lacking rainfall and inadequate distribution and extreme heat. Previous studies stated that plant water parameters and growth characteristics such as plant height, fresh and dry weight of root, stem and leaf, which is known as the first reaction of plants, were decreased under drought stress. Therefor it is necessary to use practices with objectives to decease the effects of drought stress on plants and increasing water use efficiency. Several studies showed that various morphological and physiological characteristics in plants were influenced by ascorbic acid. In fact, ascorbic acid increased plant resistance to drought stress. The purpose of this research was to investigate the effect of ascorbic acid application on growth traits of ‘Baghmalek’ olive under 100%, 66% and 33% ETcrop < /sub> by analyzing growth traits and relative water content, stem water potential and stomata resistance.

This research was carried out in order to assess the effects of three levels of water deficit (100, 66 and 33 percent of evapotranspiration (ETcrop < /sub>)) and four concentrations of ascorbic acid (0, 250, 500 and 750 mg l-1) on some growth and physiological parameters of young olive plants cv. ‘Baghmalek’as a factorial experiment based on a randomized complete block design with three replications. Fresh and dry root, stem and leaf weight, leaf number, leaf area, stem diameter, relative water content, stem water potential and stomata resistance were measured in this research. Two years old olive trees (Olea europaea cv. ‘Baghmelak’) were used. Seventy two plants were grown in 10 L pots, containing a mixture of field soil: sand: manure (1:1:1). Plants were sprayed with four concentrations of ascorbic acid and irrigated every 10 days, based on the amount of evapotranspiration of plant (ETcrop < /sub>). Parameters such as relative water content, stem water potential and stomata resistance were measured at last week of the experiment and the other parameters were measured every week. Data analysis were performed using MSTATC software and means comparison were carried out by Duncan's multiple range test (DMRT) at 5% and 1% of probability levels.

The results indicated the growth quality was better in plants treated with 250 mg l-1 ascorbic acid under water stress. Fresh and dry weight of root, stem and leaf growth, stem diameter, leaf number, leaf area were higher in plants treated with 250 mgl-1 ascorbic acid than untreated plants. Interaction between water deficit stress ×ascorbic acid revealed information in plant characters such as fresh and dry weight, stem diameter and leaf area simply declined as sources of water (from 100 to 66 and 33 percent) become limited, in particular in the trees which not receiving ascorbic acid treatments. However, application of 250 and 500 mg l-1 ascorbic acid enhanced the amount of relative content of leaf and water potential of stem in trees under water deficit stress. While stomata resistance was decreased in trees receiving ascorbic acid treatments. Some researcher declared that limitation of photosynthesis could be one of the most important factors for decreasing growth under water deficit stress. In addition, relative water content, cell turgor potential, reduced cell division, cell enlargement and growth plant could be affected by water deficit stress. Also the results indicated that leaf area (5952 cm), leaf number (151.7), stem diameter (6.49 mm), stem length (63.33 cm), root dry weight (18.16 g) and leaf fresh weight (9.35 g) were obtained in irrigated plants with 33% ETcrop < /sub> and untreated with ascorbic acid. Our results showed leaf number (158.7), stem length (74 cm), root fresh weight (78.08 g), stem fresh and dry weight (46.45 and 28.43 g, respectively) and leaf fresh and dry weight (13.35 and 8.45 g, respectively) were highest in irrigated plants with 100% ETcrop < /sub> and treated with 250 mg l-1 ascorbic acid.

Water deficit stress could affect directly on relative water content, cell turgor potential and reduce cell division, cell enlargement, plants photosynthesis and plant growth. The use of ascorbic acid could effect on plants resistance to drought. In addition, various morphological and physiological traits could be influence by ascorbic acid. The results of this research indicated that 250 mg l-1 ascorbic acid concentration had more effects on water deficit and it seems ascorbic acid can be used to reducing the negative effects of drought in some regions that rainfall shortage and drought is important problems.