Masters Degrees (Viticulture and Oenology)

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Browsing Masters Degrees (Viticulture and Oenology) by Subject "Abscisic acid"

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    Bunch quality and fertility of Vitis vinifera L. cv. Prime as affected by gibberellic acid (GA3) and s-abscisic acid (s-ABA).
    (Stellenbosch : Stellenbosch University, 2022-12) Masikane, Nonkululeko Nosipho; Avenant, Eunice; Avenant, J. H. ; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Table grapes are one of the most cultivated, economically important fruit crops in the world and is one of the major fruit industries in South Africa. There is an increase competition in the market that leads to an increase production costs for South African table grape industry, to produce quality grapes that meet market requirements nationally and internationally. Market requirements for grapes are consumer driven, and are based on bunch structure, berry size, colour uniformity, flavour, texture, seedlessness and firmness. Plant growth regulators (PGRs) have become an important tool in producing grapes of high export quality, and to meet these market requirements. Gibberellic acid (GA3) is one of the registered plant growth regulators that is used as a chemical thinner in the grapevine, it is has been found to play a role in berry set, thinning and development. The effectiveness of PGRs dependent on cultivar, application time and concentration. This study aimed at establishing the effect of gibberellic acid (GA3) and abscisic acid (s-ABA) for thinning, combined with GA3 for berry sizing (applied at the recommended dosages, using different application volumes obtained with commercial spray equipment), on fertility of a 5-year-old Vitis vinifera cv. Prime block, grafted onto Ramsey rootstock on the farm Newgro at Kanoneiland in the Orange River Region. Four thinning treatments were combined with four berry sizing treatments, resulting in 16 treatment combinations. The thinning treatments comprised of a Control (No thinning); 1 ppm GA3 at 10% set and 3 days later; 1 ppm of GA3 x 5, with the first application at 10% set, followed by four more applications at 3-day intervals; and 1 ppm GA3 plus 400 ppm s-ABA at 10% set, followed by 1 ppm GA3 3 days later. All thinning treatments were applied at a volume of 1000 L.ha-1 with a Nobili 2000 T mist blower spray pump. The berry sizing treatments, applied at 7 to 8 mm and 8 to 10 mm berry diameter, respectively, comprised of a Control (Dipping) and three treatments applied by spraying. The same active ingredient dosage (2 x 20g GA3 ha⁻¹) was used for all treatments, however different application volumes were used for the spraying treatments (90 L ha-1 with an electrostatic spray pump (ESS); 250 L.ha-1 and 500 L.ha- 1 respectively with a Cima A T50S2.15.L11 mist blower spray pump. Bunches of all treatments obtained commercially acceptable bunch lengths (>20 cm) and Extra-Large berry size (> 18 mm in diameter). The control had the most compact bunches, but there was no significant difference between the three chemical thinning treatments, regarding bunch length, bunch compactness, berry size and berry size distribution. Therefore, producers could use any of these three chemical thinning treatments for Prime. There was a tendency that the largest berry size was obtained with the Dipping and ESS berry sizing treatments. Although there were significant differences, the percentage of extra small berries of all sizing treatments was very low (< 1) in both seasons. Potential fertility was assessed through forced budding in a glasshouse and bud dissections. Actual fertility was assessed in the vineyard. None of the thinning or sizing treatments negatively affected fertility. All treatments obtained commercially acceptable levels (> 80%) of bud break (ranging from 92 % to 97%) and fertility (more than one bunch per sprouted bud). Fertility was not affected by the GA3 treatments applied over three consecutive seasons, probably due to the dosage range used (1 to 5 g.ha-1 for thinning and 40 g.ha-1 for berry sizing). When making the final decision of which chemical thinning treatment and which berry sizing application technique to use, the effect on berry size and bunch quality should also be considered. None of the treatments evaluated negatively affected berry size and bunch quality. Any of the application techniques evaluated could be used, if GA3 within the recommended dosage range is used and applied at the recommended phenological stages for Prime. This study also provided data on the efficacy of GA3+ABA as thinning agent for table grapes, to be used to extend the registration of s-ABA on table grapes to include its use as a thinning agent.