Selma Pete is a white seedless “Thompson-type” raisin grape from the USDA-ARS, selected by Ramming and Tarailo (Okie, 2002) and named after former UC Davis viticulture specialist L. Peter Christensen. Selma Pete was selected for its early maturity, ripening approximately 14 to 21 days earlier than ‘Thompson Seedless’, making it suitable for dry-on-vine (DOV) (Fidelibus, 2021; Petrucci, 2002). Selma Pete is currently the earliest-ripening Thompson-type raisin grape grown in California. It is less productive than Fiesta, but ripens sooner, dries faster, and usually produces a higher proportion of ‘B and better’ raisins (Fidelibus et al., 2008; Fidelibus, 2021). Selma Pete berries have the highest titratable acidity of Thompson-type raisin grape varieties, and the raisins are tarter as a result (Parpinello et al., 2012).
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Solbrio is an early-season black-skinned table grape (Vitis vinifera L.). Solbrio vines produce large berries with a crunchy texture and full color without the need for plant growth regulators. Berry taste is sweet and neutral. This variety is licensed exclusively to the California Table Grape Commission.
Fiesta is a white seedless “Thompson-type” raisin grape from the USDA-ARS, selected by Weinberger and Loomis (1974). Selected for its early maturity, Fiesta ripens approximately 10 to 14 days earlier than ‘Thompson Seedless’, making it less susceptible to rain damage and more suitable for dry-on-vine (DOV) raisins (Fidelibus, 2021). Raisin varieties that ripen earlier than Fiesta have since been released, but Fiesta remains popular because it is among the most productive raisin grapes available, and ripens early enough to DOV. However, Fiesta’s large crops tend to limit soluble solids accumulation, and thus result in lower raisin quality compared to other Thompson-type DOV raisin grapes (Fidelibus et al., 2008; Fidelibus, 2021). Therefore, the need to balance acceptable soluble solids accumulation, which is critical for raisin yield and quality, against timely cane severance, which is critical to ensure adequate drying, is more difficult for Fiesta than it is for varieties such as Selma Pete or DOVine, which ripen sooner than Fiesta (Fidelibus, 2021). Fiesta is also particularly susceptible to powdery mildew, and the fruit may have fewer but larger seed traces than Thompson Seedless (Christensen et al., 1983).
Sunpreme is a white seedless raisin grape bred by David Ramming, USDA-ARS. It is the first raisin variety to spontaneously dry-on-vine, without cutting canes or otherwise separating the fruit from the vine. It has fruitful basal nodes and may be spur-pruned. The combination of spontaneous drying and fruitful basal nodes should make it possible to harvest and prune Sunpreme with machines, a degree of mechanization that is not possible with other raisin varieties. However, Sunpreme is also prone to preharvest fruit drop caused by the abscission of cluster branches. Compared to other Thompson-type raisin grapes, Sunpreme has larger, rounder, berries, and heavier raisins that are lighter in color. Sunpreme grapes and raisins also have a pleasant, mild, Muscat flavor.