The Effect of Winter Foliar Spraying of Urea on the Changes of Plant Hormones in Leaves and Buds and Its Relationship with Flowering in 'Kinnow' Mandarin

Document Type : Full Paper

Authors

• Fatemeh Karamnezhad ¹
• Nooroallah Moallemi ²
• Esmaeil Khaleghi ³

¹ Department of Horticultural Science, Faculty of Agriculture, Shahid Chamran University of Ahvaz,, Ahvaz,, Iran

² Department of Horticultural Science, Faculty of Agriculture. Shahid Chamran University of Ahvaz, ahvaz, Iran

³ Department of Horticultural Science, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Ahvaz, Iran

Abstract

Keywords

• Abscisic acid
• Auxin
• Gibbrellin
• Urea

Main Subjects

• Fruit Science

Extended Abstract

Introduction

 Nitrogen plays an important role in the nutrition management of citrus trees and the production of uniform and quality products. The role of nitrogen in vegetative and reproductive growth, resulting in an increase in yield, as well as the relationship between hormones and flower induction and fruit set are truly well-known in various plant species. It has been reported that ABA and IAA act to coordinate demand and acquisition of nitrogen. This study aimed to better understand of the role of hormones in the morphology of the tree and also mechanisms regulating the alternate bearing of Kinnow mandarin and methods to reduce this problem. The hormonal changes in leaves and nodes of Kinnow mandarin as affected by different concentrations of urea were investigated, to determine the optimum amount and foliar spraying time of urea, for higher yield and uniform fruits.

Materials and Methods

This study was conducted from late December 2016 through late January 2017, on the 17-year-old and uniform 'Kinnow' Mandarin (Citrus reticulate Blanco) trees, grafted on bitter orange (Citrus aurantium) rootstocks in a commercial orchard located in Dezful, Khuzestan Province of Iran. The orchard was established at 32 ̊, 24′ N altitude, and 48°, 23′ E latitude, and 140 m above sea level. The distance of the trees were 6 meter on and between the rows and were irrigated using a dirp system. Soil chemical and physical properties were analyzed and the results were illustrated. Different concentration of urea (0, 0.75 % and 1.5 %) (having forty six percent active ingredient of nitrogen) at the different times (22 Dec 2016 and 5, 22 Jan 2017) were sprayed on the selected trees in the winter. In order to extract polyamines and N fractions from leaves and nodes of the treated trees, 1, 3 and 5 weeks after the foliar treatments, samples of branches from four sides of the trees were collected and immediately frozen with liquid N before transferring to the laboratory. The concentration of N in dried material of leaves and nodes were determined using colorimetry as described by Walling et al. (1989). Hormones concentrations ABA, IAA and GA₃ were determined using HPLC according to the method described by Rivier and Crozier (1987).

Results and Discussion

The results indicated that after foliar application of urea, the highest leaf and node nitrogen content was obtained from trees sprayed with 1.5% concentration of urea on Jan 5 in the off-year. The highest leaf and node GA₃ content was recorded from untreated trees in the on-year. The highest amount of ABA in leaves was reported at 0.75% urea concentration on January 20. The highest leaf and node IAA content was obtained from plants sprayed using 1.5% concentration of urea in the off-year. Also, different concentrations of urea increased the number of flowers, so that the highest number was observed in the maximum urea concentration (1.5%). The hormones content in leaves and nodes varied according to the urea concentration and the spray time. Results showed significant differences in IAA, ABA and GA₃ between On- and Off- cropping years in leaf and node of 'Kinnow' trees.

Conclusion

The results of this experiment showed that spraying urea on 'Kinnow' Mandarin trees had a significant effect on the level of plant hormones in leaves and nodes. The highest amount of abscisic acid and auxin in leaves and nodes obtained after foliar spraying on 15th of January with urea concentration of 1.5%. Therefore, it is recommended that if the amount of leaf nitrogen is less than 2%, in the late fall, 'Kinnow' Mandarin trees should be sprayed with a concentration of 1.5% to 1.5% urea in order to reduce alternate bearing.