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Effect of gibberellic acid, CPPU and harvest time on browning of Vitis vinifera L. 'Regal Seedless'
- Avenant, J. H.
- Acta horticulturae 2017 no.1157 pp. 357-366
- Vitis vinifera, brix, commercial farms, cultivars, exports, friction, gibberellic acid, harvest date, rivers, rootstocks, sunburn, table grapes, South Africa
- The aim of this study was to investigate gibberellic acid (GA3) and N-(2-Chloro-4-pyridyl)-N-phenylurea (CPPU) treatments which can reduce or eliminate browning of white table grape cultivars. During two consecutive seasons (2008/09 and 2009/10), this study was conducted on mature 'Regal Seedless' with Ramsey as rootstock, on two commercial farms in the Berg River Valley. Twenty treatment combinations of GA3 (no GA3, 10, 20, 30 and 40 ppm) and CPPU (no CPPU, 1, 2 and 4 ppm) were applied and replicated three and four times respectively. Grapes from each treatment were harvested at 16 °Brix (1st harvest), 20 °Brix (2nd harvest) and 24 °Brix (3rd harvest). After packing as for export, cartons were stored at -0.5°C for 8 weeks plus 4 days at 7.5°C, before browning evaluation. Although delay in harvest time, resulted in decreased net-like and friction browning, an increase in mottled, physical, sunburn, peacock and internal browning occurred. Harvest time had a significant effect on browning of grapes. Grapes harvested at the second harvest date and last harvest date had significantly more mottled, physical, sunburn and peacock browning, compared to grapes harvested at the first harvest date, while less net-like and friction browning were recorded. Grapes harvested at the last harvest date had significantly more internal browning. Delay in harvest time, resulted in decreased net-like and friction browning. Net-like browning was decreased significantly with the use of GA3 only for grapes harvested at the first harvest date and second harvest date, but no significant effect was obtained between different GA3 concentrations. Sunburn browning was decreased with the use of CPPU. The results of this study indicated that GA3 can be used to decrease net-like browning of grapes harvested during the earlier part of the harvesting window (17 to 18 °Brix), while CPPU applied can be used to decrease internal browning of grapes harvested during the latter part of the harvesting window (approximately 24 °Brix).