Survivor Trees May Hold Hope for Getting Past Greening

In our ongoing struggle with citrus greening, growers are on the lookout for two potential beacons of hope — escape trees and survivor trees.

Escape trees are trees that have somehow avoided infection by citrus greening disease despite being in an area where the disease is prevalent. They might be often found in the same groves as infected trees but have not shown symptoms of the disease. These trees might have some natural acquired resistance or might have avoided infection due to various environmental or management factors. 

At this time, no known escape trees have been identified.

However, there are a few groups of survivor or tolerant trees. These are trees that are infected with greening but have managed to survive and continue to produce fruit. Unlike escape trees, survivor trees are affected by the disease but have shown a remarkable ability to cope with it and remain productive. Survivor trees are of particular interest because they may have genetic or other characteristics that allow them to tolerate the disease better, which can be useful for breeding more resistant citrus varieties or developing better management practices. 

One such grove is in the Howey-in-the-Hills area. Gary England, a UF/IFAS Extension Agent IV Emeritus, has in-depth knowledge of these trees — even if no one is sure what variety the trees are.

“These are an early sweet orange,” England says. “We thought they might have been Hamlins at first, but these are seedy, and have a better juice quality than Hamlins.” The fruit from these trees usually contain 10-14 seeds per fruit; Hamlins typically have no more than three seeds, if any. The trees are also not Parson Brown oranges —  the fruits’ characteristics, like shape and the pebbling on the rind, are different.

The area being monitored holds approximately 40 trees, each visibly infected with greening, but still continuing to produce quality fruit. “It’s what you’d expect to see if greening wasn’t an issue,” England adds. “These trees are maintaining their production levels.”

Age could be a factor in these trees since the trees are approximately 38 years old, and were well established long before greening became a factor. “These were planted in 1987 to replace trees lost in the big freezes in ’81, ’83, and ’85. And then these survived the freeze of ’89.”  

The Florida Department of Agriculture and Consumer Services has collected budwood samples from most, if not all, of these trees. Scientists, such as Dr. Manjul Dutt, are working diligently to discover whether these or other survivor trees hold the answers to Florida’s greening problem.

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