The effect of naphthalene acetic acid on growth, yield and fruit quality of okra cv. Kano Dwarf

Abstract
Background and objectives: Okra is an important economic crop that grows in tropical and subtropical regions of the world. Recently with the identification of okra properties, some studies to produce high-performance and high quality have been carried out. The use of plant regulators affects growth and qualitative characteristics of the plants. However, to determine the appropriate concentration for each plant, special investigation should be performed, because using inappropriate concentrations may have a negative impact on yield and quality of crops. Naphthalene acetic acid is one of the synthetic auxin compounds classified as a growth regulator and reproductive development. So this study was conducted to evaluate the effect of naphthalene acetic acid and determine the appropriate concentration for growth, yield and quality improvement of okra.
Materials and methods: This research was conducted in research farm of University of Zanjan. Experiment was set out in a randomized complete blocks design with three replications. Treatments include four levels of naphthalene acetic acid (0, 25, 50 and 100 mg.l-1) that were applied as foliar application. NAA concentrations used in NAA have been selected based on studies on Malvaceae family plants. Growth traits (plant height, number of branches, number of leaves, leaf area and ...), Quantitative traits (number of fruits, fruit fresh weight, total yield, number of seeds, weight of one thousand seeds and …) and fruit quality traits (vitamin C, total carbohydrates, mucilage percent and nitrogen, phosphorus and potassium contents of fruit) were studied.
Results: The results showed that naphthalene acetic acid had significant effect on growth, yield and fruit quality of okra. The highest plant height, leaf number, leaf area, number of fruits, yield, fruit dry matter, weight of one thousand seeds, total chlorophyll content and vitamin C were obtained with application of 25 mg.l-1 and the lowest values of this traits was observed in 100 mg.l-1 naphthalene acetic acid. The shortest time from flowering to harvest fruit observed in 25 mg.l-1 naphthalene acetic acid. The highest value of total carbohydrates, mucilage percent and amount of phosphorus and potassium of fruit were obtained in 100 mg.l-1 naphthalene acetic acid and the lowest values of this traits was observed in control plants.
Conclusion: On the basis of these results, application of naphthalene acetic acid affects growth, yield and fruit quality of okra. Growth and yield significantly decreased in response to increase in NAA concentrations. According to the results, 25 mg.l-1 of naphthalene acetic acid is recommended to improve growth and fruit yield of okra.