Response of 2A Clone grape to GA3 sprays for berry thinning as influenced by cane regulation on two training systems under tropical conditions

Abstract

With an aim to minimize manual thinning in 2A Clone of ‘Thompson Seedless’ grapevine trained on bower and extended Y trellis and grafted on “Dogridge” rootstock, investigations were carried out in growers’ vineyards around Nashik, Maharashtra during 2013–14. Gibberellic acid (GA3) was sprayed at 10 ppm thrice or 15 ppm twice. Since the response to GA3 for berry thinning is stage specific, attempts were made to induce uniform bud break by retaining the canes of uniform diameter, consequently achieve uniformity in the stage of panicles that is ideal for GA3 sprays. Efficacy of GA3 sprays in reducing the cluster compactness on different training systems (bower or extended Y trellis) and with cane regulation was assessed. Less cane diameter but more uniform bud break was observed on extended Y trellis and cane regulated vines. Uniformity in the stage of panicle was not influenced by either the training system or cane regulation. Clusters were less compact in spite of the larger berries on Y trellis with two sprays of GA3 @ 15 ppm. Although this combination was highly effective in reducing the cluster compactness, clusters in all the treatments were in the range of loose to wellfilled. Cane regulation coupled with two sprays of GA3 @ 15 ppm or retention of all canes coupled with three sprays @ 10 ppm resulted in more yield. These interactions were more pronounced on bower. Total soluble solids content and berry specific gravity were more on extended Y trellis while the titratable acids content was less on this trellis in cane-regulated vines. Taking cluster compactness, yield and quality into consideration, two sprays of GA3 at 15 ppm on extended Y trellis but three sprays @ 10 ppm on bower, with or without cane regulation were found best.