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).
Origins and History
Selma Pete was the result of a complex cross of other V. vinifera varieties, selected by Ramming and Tarailo, and released by the USDA-ARS in 2001.
Selma Pete is suitable for head or cordon training (Fidelibus et al., 2008), but basal buds have low fertility, so it must be cane-pruned, and canes are also necessary for dry-on-vine since cane severance initiates the raisin-drying process (Fidelibus et al., 2020). Selma Pete is a moderate to vigorous variety which sometimes produces shoots, clusters, and tendrils with atypical morphology, including bifurcated or fasciated shoots and clusters, and tendril-like shoots. The canopy of Selma Pete tends to be less dense than Fiesta, due to weaker lateral shoot development. Leaf blades are five-lobed, with toothed margins. The central lobe of each leaf is elongated, and the main veins in each lobe often have some pink or red color at their base.
Basal bud fruitfulness is low, so Selma Pete vines are cane pruned to achieve adequate yield, and cane-pruning is necessary for DOV, since cane severance initiates the drying process. Selma Pete is prone to zinc deficiency, especially on certain rootstocks such as Freedom. Zinc deficiency can be corrected with dilute foliar sprays applied prebloom to bloom (Christensen, 2000). Clusters are medium (average 1 lb), conical, with medium (2.2 g), ovoid-elongated berries. Fresh berries are astringent, but dried berries are not. Selma Pete typically ripens in early to mid-August in the San Joaquin Valley, and typically retains higher titratable acidity than other raisin grapes at the same level of soluble solids (Fidelibus, 2021). Selma Pete berries have small seed traces.
Selma Pete is generally grown for DOV raisins, with either open-gable (Fidelibus et al., 2008) or overhead arbor trellises (Fidelibus, 2021). Vines on either type of trellis can be head-trained or cordon-trained, and cane pruned. It may be easier to maintain spur positions on head-trained versus cordon-trained vines, but cordon training can facilitate canopy management and pruning. Selma Pete has longer internodes than other raisin varieties, and pruners thus need to leave longer canes to retain a similar number of nodes, as compared with other varieties. Fruit on an open-gable trellis may dry better than they do on an overhead arbor, as canopy management practices, such as hedging, can allow for better sun exposure. However, vines on an overhead arbor have a higher yield potential. Production data have been published in open-access journals and are available online (Fidelibus et al., 2008; Fidelibus, 2021). Cost and return studies for DOV raisin grapes on open gable and overhead arbor trellises are available (Fidelibus et al. 2016a; Fidelibus et al., 2016b).
Selma Pete DOV raisins have finer wrinkles than other Thompson-type raisin grapes (Angulo et al., 2007; Parpinello et al., 2012) and typically have excellent quality grades. Selma Pete berries generally retain higher acid levels than other raisin grapes, and their raisins have a tarter flavor as a result (Angulo et al., 2007, Parpinello et al., 2012). Raisin color can be dark and uniform (Angulo et al., 2007), or lighter and variable (Parpinello et al., 2012) depending on soluble solids (Uhlig and Clingeleffer, 1998), or sun exposure.
Fidelibus, M.W., L.P. Christensen, D.G. Katayama, and D.W. Ramming. 2008. Early-ripening grapevine cultivars for dry-on-vine raisins on an open-gable trellis. HortTechnology 18:740-745.
Angulo, A., M.W. Fidelibus, and H. Heymann. 2007. Grape cultivar and drying method affect sensory characteristics and consumer preference of raisins. Journal of the Science of Food and Agriculture 87:865-870.
Parpinello, G.P., H. Heymann, S. Vasquez, K.A. Cathline, and M.W. Fidelibus. 2012. Grape maturity, yield, quality, sensory properties, and consumer acceptance of Fiesta and Selma Pete dry-on-vine raisins. American Journal of Enology and Viticulture 63:212-219.
Fidelibus, M.W. 2021. Grapevine variety and number of canes affect dry-on-vine (DOV) raisin production on an overhead arbor trellis. Horticulturae 2021, 7(10), 356; DOI:10.3390/horticulturae7100356
Cathline, K.A., G. Zhuang, and M.W. Fidelibus. 2020. Productivity and fruit composition of dry-on-vine raisin grapes pruned to 15- or 20-node canes on an overhead trellis. Catalyst: Discovery into Practice. DOI:10.5344/catalyst.2020.20002
Christensen, L.P, and W.L. Peacock. 2000. Mineral nutrition and fertilization, p. 102-114. In: L.P. Christensen (ed.). Raisin production manual. University of California Agricultural and Natural Resources, Oakland.
Fidelibus, M.W., A. Ferry, L. Jordan, G. Zhuang, D.A. Sumner, and D. Stewart. 2016a. Sample costs to establish a vineyard and produce dry-on-vine raisins - open gable trellis system. University of California Cooperative Extension, Department of Agricultural Resource Economics, Davis.
Fidelibus, M.W., A. Ferry, L. Jordan, G. Zhuang, D.A. Sumner, and D. Stewart. 2016a. Sample costs to establish a vineyard and produce dry-on-vine raisins – overhead trellis system. University of California Cooperative Extension, Department of Agricultural Resource Economics, Davis.