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Managing irrigation efficiently is paramount given the uncertainty in the future availability of water and rising demand for this resource. Scheduled irrigation significantly influences vegetative growth through improving crop physiology and nutrient uptake and use efficiency. Influence of different irrigation treatments (100%, 75%, and 50% volume of Class A pan evapotranspiration) applied at four different phenological stages (flowering and fruit set (C1), fruit growth stage (C2), pre-harvest stage (C3), and throughout the growing season (C4)) through drip along with a control (rainfed) on leaf physiology, nutrient content, and uptake through gene expression was studied on Super Chief Sandidge variety raised on M9T337 (5 and 6 years old) grown at a spacing of 1.5 × 3 m (2222 plants/ha) under high density condition of Kashmir Himalayan range of India. A comparison of data reveals that drip irrigation at 100% Crop evapotranspiration (ETc) increased leaf area by 60% compared to rainfed conditions. Leaf area significantly increased in plants irrigated throughout the growing season (C4) and during flowering and fruit set stage (C1). Irrigation amount likely does not have any influence on leaf development after the fruit growth stage. Stomatal opening and their size greatly vary from no irrigation to optimum irrigation in these plants. High density apple trees exposed to optimum irrigation levels (100% and 75% ET) had significantly higher concentrations of nutrients (N, P, and K) in their leaf tissues. The concentration of Ca and Mg content in leaf tissues are greatly influenced by the optimum supply of water during the early growth stages of apple growth. The availability of water significantly influences nutrient transporter gene expression and thus nutrient uptake by regulating such transporter genes. It is therefore observed that proper irrigation during C1 and stage C2 stage are the critical growth stages of apple for optimum leaf physiological activity and proper nutrient uptake.

The present investigation entitled “Regulation of growth, fruiting and biochemical characteristics in Fuji Zehn Aztec and Red Braeburn apple cultivars through application of growth retardants under high density planting system” was conducted in the Experimental Block of the Division of Fruit Science at Sher-e-Kashmir University of Agricultural Sciences & Technology of Kashmir, Shalimar campus, Srinagar (J&K) during the years 2020 and 2021. Four-year-old apple cultivars Fuji Zehn Aztec and Red Braeburn on M9-T337 planted at a distance of 3×1 meter of uniform age, vigor and girth were used for the study. The experiment comprising of seven treatments viz., control, prohexadione-calcium @125 ppm, prohexadione-calcium @250 ppm, prohexadione-calcium @500 ppm, paclobutrazol @200 ppm, paclobutrazol @400 and paclobutrazol@600 ppm was laid out in randomized complete design with three replications. The chemicals were sprayed one week after petal fall, three weeks after 1st spray and three weeks after 2nd spray. Paclobutrazol@600 ppm resulted in maximum reduction in vegetative growth parameters in both the apple cultivars under study.

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