Effects of growth regulators and bunch trimming on size, maturity and yield of sultana grapes

Abstract

Three experiments were done over two seasons on the effect of gibberellic acid (GA) and parachlorophenoxyacetic acid (PCPA) sprays and bunch trimming on the yield, berry characters, maturity, and bunch quality of sultanas. GA applied at the shatter stage at 10 p.p.m. increased berry size and bunch quality of fresh fruit. When applied at full bloom, berry size was increased and earlier maturity was induced but berry set and yield were reduced. If applied at commencement of bloom. GA caused considerable thinning and the bunches were unattractive. Splitting the application into two 5 p.p.m. applications at commencement and full bloom was also unsatisfactory. A combined spray of PCPA and GA at shatter stage retarded maturity but increased berry size and yield over GA alone. It was shown that PCPA should be applied separately several days after shatter to avoid retention of shoe bellies. GA increased berry size mainly by elongation. Addition of PCPA produced larger berries of more normal shape. Bunch trimming decreased total yield of most treatments, but did not increase quantity of marketable fresh fruit. However, in general, berry length, diameter, and weight were increased by trimming. The importance of thorough wetting of the bunches by gibberellic acid sprays was demonstrated in a dipping experiment.