Effects of nano micronutrient foliar application on physiology and yield traits of kinnow mandarin (Citrus reticulata Blanco)

Despite the recognized importance of micronutrients in citrus production, limited research has been conducted on the synergistic effects of nano boron (nB) and nano zinc (nZn) in improving growth, yield and fruit quality of kinnow mandarin under Punjab’s agro-climatic conditions. A field experiment was conducted at the Department of Horticulture, Lovely Professional University, Punjab, to evaluate the effects of foliar application of nB and nZn on the vegetative growth, productivity and qualitative traits of kinnow mandarin (Citrus reticulata Blanco). The study followed a randomized block design (RBD) comprising nine treatments replicated thrice, using 27 uniform, twelve-year-old trees grafted onto rough lemon (Citrus × jambhiri Lush.) rootstock. Foliar sprays were applied twice at varying concentrations. Among all treatments, T9 [nB (60 mg/L) + nZn (200 mg/L)] significantly outperformed others in all evaluated parameters, showing the highest increment in tree height (5.94 %), canopy spread (6.06 % East-West; 6.23 % North-South), initial fruit set (53.17 %), final fruit retention (24.30 %) and ultimately yield (81.07 kg/plant). Fruit morphology and quality attributes were also significantly improved, including fruit size [length (5.92 cm) × diameter (6.75 cm)], number of fruits (512.67), fruit weight (158.20 g), rind weight (27.85 g), weight of pulp (130.35 g) and pulp percentage (82.40 %). Additionally, notable enhancements were observed in shelf life (8.68 days), total soluble solids (11.50 °Brix), total sugars (8.97 %), reducing sugars (3.92 %) and non-reducing sugars (5.05 %). Treatments T6 and T8 also showed significant improvements, though they were less effective than T9. Overall, the combined foliar application of nB and nZn proved highly effective in enhancing vegetative, reproductive and postharvest qualityattributes of kinnow mandarin.