Promising Budwood: Propagating the Donaldson Sweet Orange

Propagating citrus budwood involves taking a cutting, or scion, from a healthy citrus tree and grafting it onto a rootstock. This method preserves the desirable traits of the parent tree, such as fruit quality maturity to flower fruit or disease resistance. It’s a quicker and more reliable way to produce trees with known characteristics compared to growing from seed, which can result in variability in traits. The budwood cutting is usually grafted onto a rootstock that determines the tree’s size and growth characteristics.

Florida Department of Agriculture and Consumer Services (FDACS) has an established protocol for the production of budwood. Citrus trees may carry pathogens or diseases that are detrimental to tree growth and fruit production and may affect neighboring groves. Only by using budwood from pathogen-tested trees that are protected in greenhouse structures and are under inspection can the citrus industry achieve any degree of protection from harmful pathogens. All citrus propagation must be done in an approved, enclosed structure that is inspected by FDACS’ Division of Plant Industry. Growers cannot undertake this process themselves.

Due to a few varieties showing strong HLB resistance, the budwood propagation process has been expedited for these in order to get more trees into groves to help bolster the citrus industry.

One of the most promising of these varieties is the Donaldson orange, a sweet orange rediscovered on the Whitmore Foundation Farm in 2021. The Donaldson tree stood out in the grove, having a healthy appearance despite high HLB infection rates nearby. Initial trials with the Donaldson budwood were promising, and the tree was approved for expedited budwood in 2022.

Early estimates indicate that propagation efforts could produce as many as 1,500-2,000 viable trees, which could then provide 22,500-30,000 additional eyes to be budded.

The CRAFT Foundation approved 11 projects in their Program for Expedited Propagation (PEP), which include Donaldson oranges, alongside other promising varieties, such as Parson Brown, Carney 1, Carney 2, and Roble. These will be grown in comparison with Hamlin oranges, serving as a control.

To be clear, the Donaldson is not immune to HLB, but appears to be highly tolerant. Donaldson trees show some HLB symptoms, but it has still maintained a dense canopy, a normal crop load, and has shown no premature fruit drop in holding firm to the tree.

Initial results and observations are promising, but only time will tell how the Donaldson orange will impact the Florida citrus industry.

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