Potential of thidiazuron and arginine foliar spray to enhance vegetative growth and chemical composition of Washington navel orange saplings

Abstract

The slow vegetative growth of citrus saplings during the nursery stage prolongs their nursery residence time and increases production costs. Therefore, a study was carried out on Washington navel orange saplings from April to December 2025 in the shade house at Department of Horticulture and Landscape Gardening, College of Agriculture, University of Anbar, Iraq, to show the effect of spraying with the growth regulator thidiazuron (TDZ) at concentrations of 0, 5, 10 and 15 mg L-1 and arginine at doses of 0, 100 and 200 mg L-1 on vegetative growth and chemical content. The experiment was conducted using a factorial design within a randomised complete block design (RCBD) with 3 replicates. The results indicated that both studied factors significantly affected all the examined traits, particularly at higher concentrations. The combined application of TDZ (15 mg L-1) and arginine (200 mg L-1) significantly enhanced most evaluated parameters and recorded the highest values among treatments. It increased the number of primary branches (6.67 branch sapling-1), length of primary branches (15.90 cm), number of leaves (122.67 leaf sapling-1), total leaf area (30.42 dm2), dry weight of the vegetative growth (88.46 g) and percentage of carbohydrates in branches (9.40 %). It also improved leaf nitrogen (2.58 %), potassium (1.86 %) and total chlorophyll content (1.57 mg g-1 fresh weight). These findings demonstrate the potential of combining TDZ and arginine to improve the growth and nutritional status of citrus saplings, providing a practical approach for enhancing nursery production and sapling quality.