Rachis browning in four table grape cultivars as affected by growth regulators or packaging

• Gibberellin and cytokinin were applied to four grape cultivars according to vineyard practices.
• Rachis browning after harvest was determined by image analysis.
• None of the PGRs had a consistent effect on rachis quality and rachis thickness did not correlate to browning.
• Shelf-life to reach 50% browning was determined with grapes in open or covered punnets.
• Water loss was not the only cause of rachis browning.

Plant growth regulators (PGRs) are used to increase berry size in table grapes. The objective in this study was to determine if the levels of PGRs used commercially affected rachis postharvest quality. Three seedless table grape cultivars, ‘Mystery’, ‘Superior’, and ‘Crimson’ were treated with gibberellin (GA), cytokinin (CPPU), or both at berry diameter of 6–8 mm, while a seeded cultivar, ‘Redglobe’ was treated at 13 mm. The fruits were harvested at commercial maturity and held for 7 days shelf-life either immediately after harvest or after 2 weeks storage at 0 °C. The combination of GA and CPPU increased berry weight and diameter, and rachis diameter in all three seedless cultivars, but had minor or no effect on TSS and acidity. Rachis quality was measured by a browning scale derived from image analysis. Browning was lower after storage for rachis of ‘Mystery’ treated with GA, while the other three cultivars showed no difference between PGR treated and control rachis. Reduction of water loss by covering punnets of control clusters with microperforated film had a significant positive effect on decreasing weight loss in all cases and a positive effect on slowing rachis browning. Calculation of the shelf-life required to reach 50% rachis browning found that shelf-life was longer for the microperforated packaging as compared to open packages in all the cultivars, with stronger influence during shelf-life after storage than shelf-life after harvest. However, the data also indicated that rachis browning cannot only be attributed to weight loss, either from the whole cluster or from the rachis.