New UC Davis Prune Cultivars Prove Promising

Sarah Castro & Dr. Ted DeJong, Prune Breeders, UC Davis Department of Plant Sciences

The UC Davis Prune breeding program is eager to promote three promising new cultivars that have excited growers. The new cultivars offer a range of superior flavors, harvest dates, pruning strategies and dry away ratios. This year, all three cultivars were dried using commercial dehydrators in cooperation with interested growers.  Not all information has been returned from the dryers for the 2020 harvest, but preliminary results are very encouraging. As shown in the data table below, the dry away ratios are low, and the sugars are high for these three items. All three have been successfully pitted in previous years but will be processed again using commercial processors such as Sunsweet and Mariani.

Table 1. 2020 Summary data for the three promising new cultivars from the UC Davis prune breeding program. All items have a limited number of nursery budded trees available for growers to plant in their orchards for testing.

Solano Gold
Solano Gold (test name F11S- 38) is a vigorously growing tree that produces round, yellow fruit. It ripens one month before Improved French and starts to dry on the tree before harvest. Its ability to dry on the tree creates an unusually low dry away ratio upon dehydration. The dried fruit comes out of the dryer with a deep mahogany color and darkens as the dried fruit is stored. The 2019 fruit was pitted via an Ashlock pitter and the fruit was given away as samples during the Prune Summit in February 2020.

Yolo Gold
Yolo Gold (test name G2S- 8) is an upright growing tree that produces oval, yellow fruit. The tree is precocious and will usually produce fruit in its second leaf. The tree should not be long pruned, and crop loads are consistently high most years, thus requiring thinning. The fruit is typically larger than Improved French and has superior fresh and dried flavor in comparison to Improved French.

H13S-58
H13S-58 is a tree with yellow fruit that also begins to dry on the tree. Its fruits’ ability to dry on the tree can create unusually low dry away ratios and durable fruit that is able to withstand many hours in the bin before drying. The fruit harvests 1-2 weeks after Improved French, but has such a long harvest window, that it can be harvested early with Improved French when necessary (see Madera harvest data in Table 1). Anecdotal feedback from growers with trial trees claim H13S-58 would not need as much pruning as Improved French because it does not grow many excess branches. It might be a candidate for mechanical hedging because it does not appear to respond to pruning with excess growth. Mechanical pruning compatibility has not yet been investigated by the UC Davis breeding program. This tree is extremely precocious and will not do well with long pruning. Notes from a grower with second leaf trees said he needed to thin his second-year fruit so that it would not over-crop too early. The breeding program highly recommends to not grow too much fruit during its second leaf, otherwise the tree will not set up strong scaffolds for future crops.

Advanced Selections
In addition to these three new selections we have obtained very encouraging results from a set of six new advanced selections that include five with purple and one with yellow fruit that mature before and along with Improved French. All selections develop fruit with very high sugar content and have low dry away ratios and great taste (see Table 2). They offer differing harvest dates but produce dried fruit that would be able to be easily mixed with Improved French. We are looking for grower cooperators to plant test trees of these items.  If you are interested in becoming a grower cooperator, please notify the program manager, Sarah Castro (scastro@ucdavis.edu).

Table 2. Newest promising items available for testing from the UC Davis Prune Breeding program. All items start to dry on the tree before harvest and have had at least two years of promising fresh and dried evaluations.

The UC Davis breeding program would like to thank participating grower cooperators. Because of you, the program was able to perform multiple tests this year. A few growers not only grew the trees but helped transport fruit and encouraged their processors to get involved. The collaboration between growers, the breeding program and the processors is essential for determining the acceptability of these items for commercial production.

The prune breeding program is funded by the Prune Board of California. The goal of the breeding program is to breed new cultivars that will save growers on operational costs and stabilize prune production in California.  The main costs the program tries to reduce are drying costs (via dry away ratio) and pruning costs. The program has many new items every year that are commercially viable candidates for future release. The items in the seedling test blocks prove to be more and more remarkable as the years unfold. The program is confident that they have items that can save growers production costs and stabilize cropping. The new items in Table 2 have been budded by Sierra Gold Nursery and are ready for grower trials.

For more information about these items please contact Sarah Castro at scastro@ucdavis.edu.

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