Micronutrient dynamics in Vitis vinifera L. cv. Red Globe as influenced by bunch regulation, berry thinning and bioregulators

Abstract

An investigation was conducted during 2023-24 and 2024-25 at the Main Horticultural Research and Extension Centre, University of Horticultural Sciences, Bagalkot, to evaluate the influence of bunch regulation, berry thinning and bioregulators on petiole micronutrient status of grapevine (Vitis vinifera L.) cv. Red Globe. The experiment was laid out in a Split-Split Plot Design comprising two levels of bunch regulation (control and 30 bunches per vine), three levels of berry thinning (no thinning, 15 % and 30 %) and four bioregulator treatments (control, ABA 300 ppm, Ethrel 200 ppm and ABA + Ethrel). Petiole samples were collected at 45 and 90 days after October pruning and analysed for iron, manganese, zinc and copper using Atomic Absorption Spectrophotometer (AAS). Micronutrient content at 45 days after pruning was non-significant. However, at 90 days after pruning, vines regulated to 30 bunches per vine recorded significantly higher iron (48.68 ppm), manganese (157.60 ppm), zinc (67.88 ppm) and copper (5.71 ppm), compared to unregulated vines. Among berry thinning treatments, 30 per cent thinning recorded the highest iron (49.72 ppm), manganese (157.53 ppm), zinc (70.35 ppm) and copper (5.79 ppm), whereas the lowest values were recorded in unthinned vines. Bioregulator treatments and their interactions were non-significant. The results indicate that crop load optimization through bunch regulation and moderate berry thinning enhances micronutrient accumulation by improving source-sink balance under semi-arid tropical conditions.