Advancement of `Riesling' Fruit Maturity by Paclobutrazol-induced Reduction of Lateral Shoot Growth

in Journal of the American Society for Horticultural Science
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  • 1 Agriculture Canada Research Station, Summerland, B.C. V0H 1Z0, Canada

Paclobutrazol (PB) was sprayed on hedged `Riesling' (Vitis vinifera L.) vines at one of five concentrations (0, 1000, 2000, 3000, or 4000 mg·liter-1) as single annual applications over 3 years (1987-89). Observations were made on growth, yield, and fruit composition during the years of application and 1 year thereafter (1990) to test carryover effects. PB had no effect on vine vigor, expressed as weight of cane prunings, during the three application years, but reduced vine vigor linearly with concentration in 1990. Yield was reduced by PB in the first 2 years of the trial, while in one season cluster weight and berries per cluster were also reduced. °Brix was increased by PB during all 3 years of application; titratable acidity was reduced and pH increased in the first year of application. PB sprays significantly reduced lateral shoot length, mean leaf size on both main and lateral shoots, and total leaf area on main and lateral shoots. Winter injury to buds, cordons, and trunks was also reduced with increasing PB level. Residues of PB in fruit in the first year of application ranged from 9 μg·kg-1 at the 0-m·gliter-1 level to 638 μg·kg-1 at the 4000-mg·liter-1 level. PB shows promise as a viticultural tool for advancement of fruit maturity, with possible additional benefits such as improved vine winter hardiness. Chemical name used β -[(4-chlorophenyl) methyl]-α -dimethylethyl)-1-H-1,2,4-triazole-l-ethanol (paclobutrazol, PB).

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