Field Day Leads to Reboot of Old Citrus Varieties

By Peter Chaires

The U.S. Department of Agriculture’s Agricultural Research Service (USDA-ARS) field day on Dec. 3 at the A.H. Whitmore Foundation Farm was a productive and memorable day. The event was well attended and provided growers, nurserymen and industry leaders with an overview of essential research taking place at the farm.

The fruit display and tour drew attention to three old-line sweet oranges planted in a germplasm collection block. There was sufficient interest in these varieties to initiate an information search, as well as to engage the USDA-ARS national program staff to help determine the most expedient way to get these varieties into the hands of interested growers.

The Donaldson is producing good quality oranges that are holding well on the tree.

DONALDSON

The origin of the Donaldson is a bit foggy. We know that USDA-ARS made a seedling selection of open-pollinated seed and planted it at the old USDA Hiawassee Farm (West Orlando) in 1979. The tree was later relocated to the Whitmore Foundation Farm. The tree appears to have been propagated from the original source in 1994. The Donaldson is thought to be a true early-season sweet orange. There is one tree on Swingle rootstock, and it appears quite healthy. Fruit is well-sized, adheres tightly to the tree and is not dropping. Juice has been tested by two processors and may have potential as a blending agent.

No evidence has been found that Donaldson was ever commercialized. It will be re-released by USDA-ARS as a “germplasm re-release.” This will ultimately move it into the public domain. This is the only path forward due to an inability to clearly prove ownership. Until a certified source of budwood is available, Donaldson trees will be budded from uncertified budwood and made available to interested growers who have executed a DPI Escape Tree Permit.

TOBIAS SWEET ORANGE

The Tobias sweet orange came from Brazil. It seems to mature during the Valencia window. Like the Donaldson, the one Tobias specimen at the Whitmore Farm appears to show some useful level of HLB tolerance. The canopy is green and full, and fruit is on the tree instead of the ground. Quality appears to be better than Hamlin but not as good as Valencia.

Tobias is in the public domain. Until a certified source of budwood is available, trees will be budded from uncertified wood and made available for planting to growers who execute a DPI Escape Tree Permit. These trees will be made available on a first-come, first-serve basis.

ST. MICHAEL

Like Tobias, St. Michael sweet orange is in the public domain. The University of California Citrus Variety Collection website references this description of the St. Michael Paperrind sweet orange from The Citrus Industry (Vol. 1, 1967) book:

“The fruit of this midseason California variety is small-sized, moderately seedy, juicy and well-flavored. The rind is very thin, leathery and smooth. The tree is vigorous, upright, and productive. Said to have originated on the Island of St. Michael, Azores Islands, presumably as a seedling, this variety was named and introduced about 1870 by T. A. Garey, pioneer citrus nurseryman of Los Angeles.”

Unlike Donaldson and Tobias, St. Michael does not appear to have enhanced tolerance to HLB. What it does have is outstanding flavor. It is hoped that if paired with a more tolerant rootstock and better nutrition, that it might perform at a higher level. Commercial usefulness remains unknown, but trials should bear this out. Until a certified source of budwood is available, trees will be budded from uncertified wood and made available for planting to growers who execute a DPI Escape Tree Permit. These trees will be made available on a first-come, first-serve basis.

Stay tuned.

About the Author

Frank Giles

Editor-in-Chief AgNet Media Publications