Postharvest evaluation of cold-hardy table-grape breeding lines

The University of Minnesota grape breeding program has evaluated a small number of cold-hardy cultivars and advanced selections for postharvest storage traits. This is the first experiment for comparing advanced selections to table-grape cultivars for these traits. Nine genotypes were evaluated for cluster weight and fruit chemistry at harvest. Three clusters per genotype were packed in ventilated polyethylene bags and arranged in carton boxes. Paper pads and SO₂ pads were placed on top of the bunches in each carton. The cartons were stored at 2.2°C for 2, 4, 6, and 8 weeks. Clusters were destructively sampled at each storage time point and evaluated for change in fruit weight, berry splitting, berry decay, juice chemistry, and an overall rating of acceptability. An advanced selection, ‘MN1296’, was the top-performing seedless cultivar for overall acceptability for postharvest traits, but has berries that tend to shatter. ‘Louise Swenson’, ‘Swenson Red’, and ‘MN1296’ were rated as the best-performing lines for stem dehydration, in descending order. ‘Swenson Red’ is the largest-fruited Elmer Swenson/UMN cultivar, but has limited commercial planting because of its seeded berries; ‘Swenson Red’ also had no shattering after storage. Berry splitting was worst in ‘Louise Swenson,’ a seeded white grape with multiple uses including wine. ‘Jupiter’ had severe rachis browning after 8 weeks, but little at 2, 4, or 6 weeks, whereas ‘Vanessa’ and ‘MN1369’ both suffered from decay. ‘Jupiter’ and ‘Vanessa’ had the largest clusters, but can be grown in Minnesota with only marginal success using the J-vine training system. Additional research on bud survival and consumer preference will be needed to determine whether any of the advanced selections are suitable for cultivar release.