Studying Citrus Greening in Switzerland

Daniel Cooper Citrus Greening, HLB Management, Research

Lukas Hallman works with a tree that died from citrus greening.

Lukas Hallman is about to embark on an internship in Switzerland to investigate the vascular system of trees affected by citrus greening. Hallman is in his final year of a Ph.D. program in horticultural sciences at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Indian River Research and Education Center. He is under the guidance of Lorenzo Rossi, assistant professor of plant root biology.

“My goal is to measure tree ring width and detect shifts in wood anatomy within orange and grapefruit trees grown under the challenges of citrus greening,” said Hallman. “I will be working with trunk sections taken from 10-year-old trees. These observations will help us reconstruct how citrus trees coped with citrus greening from the day of planting to now.”

Hallman will investigate both components of the tree’s vascular system, called xylem and phloem, for two months at the Swiss Federal Research Institute WSL in Zurich, Switzerland. He will collaborate with Professor Paolo Cherubini, a senior scientist specializing in dendrosciences, the scientific study of tree rings. Cherubini is a recipient of the 2007 Nobel Peace Prize for his role as an invited expert reviewer contributing to the Intergovernmental Panel on Climate Change Fourth Assessment Report.

“Our proposal for Hallman’s study aims to unveil changes in wood structure as a part of the citrus tree’s response to citrus greening,” Rossi said. “Clogged citrus tree vascular systems prevent the trees from absorbing the necessary nutrients for the citrus trees to grow and produce high-quality fruit.”

Hallman said the phloem is the specific sieve inside citrus trees that clogs with a callous material in response to infection by the bacterium that causes citrus greening. He plans to investigate and understand phloem and xylem anatomy and tree ring formation to measure citrus physiological responses to stress. The scientists will conduct the work on grapefruit and oranges grown in Florida’s Indian River Citrus District.

“We need more information about the influence of the bacterium on phloem structure and tree and root physiology,” Hallman said. “I will access highly specialized equipment in Zurich at Cherubini’s laboratory and explore vascular systems in trunks and roots of citrus greening-affected grapefruit and sweet orange trees.”

Hallman said he and Cherubini will reconstruct the physiological history of the trees in response to citrus greening through dendrochronological and wood anatomical techniques. In addition, the researchers will measure how the trees use carbon and oxygen in response to citrus greening over the years, said Rossi.

Hallman said the studies should “allow us to identify the best water and nutrient application methods and provide more insight about how citrus trees are affected by citrus greening to advance better management of the disease.”

Source: UF/IFAS

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