DRYING RATE OF FRESH BERRIES FROM NATURAL DRY-ON-THE-VINE (DOV) GRAPE GERMPLASM
The California raisin industry is using mechanical harvest methods to increase production efficiency. Fruiting canes of raisin cultivars must be cut to induce the fruit drying process. Grape germplasm that has its fruit dry-on-the-vine (DOV) without having their canes cut have been identified. Understanding the fruit or plant charac-teristics that cause the natural drying process to occur would allow breeders to select this type of raisin grape with less field testing. The drying rates at 38°C of two natural DOV selections were compared to Summer Muscat (fast berry drying rate) and Thompson Seedless (slow drying rate). All berries compared were 14.3 mm diameter and 22°Brix determined by density flotation. The drying rate of one genotype was similar to Summer Muscat and the other dried slower than Thompson Seedless, even though both dry into raisins on the vine without cutting canes. Drying was slower for all genotypes when the pedicel was covered with wax to prevent water loss through the pedicel compared to two years when the pedicel was not waxed. Thompson Seedless drying rate was dramatically decreased by the wax compared to the other genotypes. The drying order was the same for all years except for Thompson Seed¬less, which was the slowest when waxed. The drying rate does not explain why the two natural DOV genotypes dry without cutting canes. The cultivars did not differ in cuticle or wax thickness, except one DOV selection had more wax, which should have caused slow drying rates. The DOV genotypes do not develop higher sugar levels early as might be expected. The causes that induce natural drying of grape fruit into raisins remain to be found. There may be other factors such as water transport out of the berry and through the leaves that might be causing the initiation of the natural DOV phenomena.
Ramming, D.W. (2014). DRYING RATE OF FRESH BERRIES FROM NATURAL DRY-ON-THE-VINE (DOV) GRAPE GERMPLASM. Acta Hortic. 1046, 281-286
breeding, raisin, mechanical harvest, Vitis vinifera