conference schedule and program with abstracts - Horticulture ...

P-91
Drying rate of fresh berries from natural dry-on-the-vine (DOV) grape germplasm.
David W. Ramming*
USDA-ARS San Joaquin Valley Agricultural Sciences Center, Parlier, California, USA
david.ramming@ars.usda.gov
The California raisin industry has turned to mechanical harvest 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. Identification of fruit or plant characteristics that cause the drying process to start
would be useful to aid in the selection of seedlings for natural DOV raisins. The drying rates at
38C 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 o 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 pedicle
was covered with wax to prevent water loss through the pedicle compared to two years when the
pedicle 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 Thompson
Seedless was the slowest when waxed. The drying rate does not explain why the two natural
DOV genotypes dry without cutting canes. The cuticle, wax and skin thickness is being
compared to see if they might be influencing drying rate. The DOV genotypes do not develop
high sugar levels early as might be expected. 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.
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