GROVELAND, Fla. — Matt Mattia used both hands to flip through the branch at his eye level, studying each side of every leaf as sunlight filtered from above.
“Just healthy leaves,” he said, noting the dark green color.
He turned his attention to a young fruit that was still the same color as the leaf next to it.
“That looks pretty symmetrical,” he said, plucking it for further examination. “That should develop into a nice, big orange.”
Mattia is no farmer, and the tree was no ordinary plant. He works for the United States Department of Agriculture as a geneticist. The tree has a name: Donaldson.
Mattia called it the most researched tree in the state of Florida. It’s also the tree that growers hope will save the state’s citrus industry.
“When I saw the Donaldson tree, I was like, ‘Wow, this is something that’s really unique and really different,’” Mattia said.
Decades of decline
Donaldson’s notoriety has come from its unique combination of three attributes: its status as a genetically pure orange tree, its sweet taste, and most importantly, its resistance to the Huanglongbing disease, more commonly known as HLB or “greening.”
Since arriving in the United States from Brazil, greening has killed groves across the state of Florida and contributed to a 90% decline in citrus production over the past 20 years. Leaves of infected trees appear splotchy in color and can be abnormally shaped. The tree’s fruit also takes on irregular characteristics – until the tree dies.
While it has infected almost every variety of citrus tree, it hit one of two types of orange trees particularly hard: the Hamlin variety, which fruits early in the winter before the late-season Valencia oranges came in.
Under FDA rules, Hamlins and Valencias are the two major types of oranges that are allowed to be used for Florida orange juice, Mattia explained. Without the Hamlin trees, growers’ profits suffered.
Donaldson is also an early season tree. It was planted 30 years ago when the USDA created its Groveland research farm with different citrus varieties that growers could fall back on, like a seed bank.
Mattia found it by sampling 25,000 different trees to test for infection and fruit sweetness. He found other trees tolerated greening, but their fruit was bitter, bordering on inedible, he recalled.
Donaldson, with its high sugar content, stood out.
A Hamlin tree was planted near Donaldson at the same time. Mattia pointed at the spot, which was nothing more than the remnant of a trunk sticking out of the ground and a pink ribbon tied around it.
Greening did most of the damage, and Hurricane Milton finished it off, he said.
“It just was a huge stark contrast between something that was really very, very sick and declining and something that appears to continue to produce a regular crop,” he explained. “We took the fruit, we sampled the fruit, and we tasted it, and we were like, wow, this has industry potential.”
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Road to rebound
Now that they’ve settled on a tree, Mattia and his team have been figuring out what it would take to make Donaldson a commercial success.
Several researchers analyzed the taste, which to the average palette is identical to Hamlin and Valencia. The best method to produce orange juice was also looked at, with Mattia opening a bottle that had been created using a method new to their research.
Mattia’s team is now working on the next phase of their testing: monitoring young Donaldsons that had been grafted onto dozens of different rootstocks to see which combination of plants grow the strongest and fastest.
One Hamlin tree planted among the Donaldsons as a control showed signs of greening infection. Mattia said it was highly likely many of the healthy-looking nine-month-old plants had already been hit, though as a researcher it only helped him get further to his goal.
But the USDA isn’t gate-keeping Donaldson, even though the tree itself is grown behind fences and locks.
“We’re pushing it out to commercial usage,” Mattia said. “If people want to test it in their own grove, it’s available, and we have the data and the research going on here that supports that effort.”
Florida is already on-board. Mattia said the state has propagated 18,000 Donaldsons that it’s sending to growers across the state to accelerate the adoption effort.
One of those potentially interested is Mary Graham, owner of Graham’s U-Pick Farms, who had heard of Donaldson and wanted to know how many seeds each fruit had (five to seven) and whether the fruit was edible when freshly picked (yes).
For a century, Graham’s specialized in oranges. As of this year, they only grow peaches.
“We noticed greening hitting our grove probably about 15 years ago,” she recalled. “About 10, 12, years ago, it started getting a little more aggressive. So at that point, we looked for an alternative crop.”
Like her neighbors, Graham tried different methods to save her trees. She and her husband added more nutrients to the soil and cut down on chemicals, which she said helped the trees recover.
Eventually, the disease won the battle, and her husband tore out the last of the trees in January. She’s looking to plant new seedlings for her children to eventually care for, even though she said her peaches were better for business.
“We’re hopeful about the Donaldson tree,” she said. “With that one, what else can they come up with?”
That’s what Mattia is all about. He previewed “future orange juice,” a blend of different citrus fruits that resembles orange juice but has a notable flavor difference that’s being created as an alternative to Donaldson in case the tree doesn’t work out.
“My mission is to really help people,” he said. “So if they, if the industry and the processors find utility from this tree, I feel like our mission is accomplished.”
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