Effect of Foliar Application of Castor Oil and NAA on Physicochemical Properties of Apple (Malus pumila Mill.) Fruits

Abstract

This study aimed to evaluate the effects of foliar application of castor oil and naphthalene acetic acid (NAA; commercially known as Stavals) on the physicochemical characteristics of apple (Malus pumila Mill.) fruits under Iraqi environmental conditions. The experiment was conducted during the 2024 growing season using a randomized complete block design (RCBD) with three replicates. Twenty-seven uniform trees were subjected to nine treatments, including individual and combined applications of castor oil (3% and 5%) and NAA (30 and 60 mg L ⁻ ¹). The results demonstrated that foliar treatments significantly (P ≤ 0.05) improved key physical attributes of the fruits. In particular, the combined application of 5% castor oil and 60 mg L ⁻ ¹ NAA resulted in the highest fruit moisture content and juice percentage, along with a substantial reduction in fruit cracking compared to the control. Conversely, chemical characteristics such as total soluble solids (TSS), anthocyanin content, and vitamin C showed a decreasing trend under most treatments, although the differences were not consistently significant across all treatment combinations. In conclusion, the combined foliar application of castor oil and NAA represents a promising strategy for improving the physical quality and reducing physiological disorders of apple fruits. However, further optimization is required to achieve a balance between enhancing physical traits and maintaining chemical and nutritional quality.