U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) scientists are studying the possibility of the Donaldson sweet orange replacing the HLB-ravaged Hamlin in orange juice (OJ). The scientists work at the U.S. Horticultural Research Laboratory in Fort Pierce, Florida.
Photo by Giancarlo Buzzi, USDA-ARS
While assessing citrus trees with oranges that might be used for commercial OJ production, the scientists found the Donaldson tree at the A.H. Whitmore Citrus Research Foundation Farm in Groveland, Florida. The Donaldson is a selection from the USDA-ARS variety collection that represents more than 100 years of USDA-ARS research on citrus in Florida.
“The Donaldson sweet orange tree stood out as being exceptionally healthy compared to the industry-standard trees that were planted close by and were in decline or had died,” said Matt Mattia, a USDA-ARS research geneticist. “The Donaldson tree also tested positive for the presence of Candidatus Liberibacter asiaticus, one of the presumed causal agents of HLB. This indicates that the tree may have tolerance to the disease.”
Historical records show that the Donaldson tree was first planted on the farm more than 30 years ago. Hamlin was also planted there around the same time. Both are early-season trees that mature from December to January. While Hamlin has been used in commercial OJ production for years, Donaldson has remained only on the farm.
Researchers assessed if Donaldson oranges could be a substitute for Hamlin in juice production. In the study, researchers conducted taste tests to study the differences between OJ blends using Hamlin and Donaldson oranges.
“The taste testers noted that there was a difference between the two juices,” said Mattia. “However, those differences may be explained by the lower acidity in fruits from young Hamlin trees.”
According to Mattia, Donaldson oranges could replace Hamlin oranges for commercial production since they mature in the early season and present good orange flavor. However, future research should explore whether Donaldson fruit could replace Hamlin fruit in juice by comparing fruits from trees of the same age.
More research is underway to determine if the Donaldson trees have long-term tolerance to HLB and if citrus growers can successfully plant these trees to meet the demands of commercial production. USDA-ARS researchers plan to work with research collaborators and industry partners to assess Donaldson’s tolerance to HLB in field trials and study the possible underlying genetic mechanisms responsible for tolerance.
The USDA-ARS study was published in HortScience. The research was in collaboration with the University of Florida Institute of Food and Agricultural Sciences.
Source: USDA-ARS
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