Even though almost all of Florida’s citrus trees are now affected by citrus greening, a disease that has compromised the state’s most valuable crop, growers and scientists are working to slow the disease and produce healthy fruit on trees with mild infections.
A team of seven University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) professors in two of the state’s commercial fruit production regions have broken ground on new research. The scientists will use high-end technology to write new guidelines for growers to produce healthy fruit on trees affected by citrus greening. The scientists, in the Florida Ridge area and the Indian River District, will conduct their work focusing on tree roots.
Funds for the research are provided with a grant from the Citrus Research and Development Foundation, Inc., in Lake Alfred, Florida.
“The goals for the project are to develop the industry’s guidelines to provide micro and macronutrients to trees affected with HLB (huanglongbing, or citrus greening),” said Davie Kadyampakeni, an assistant professor for citrus nutrient and water management, at UF’s Citrus Research and Education Center in Lake Alfred (CREC), in the central part of the state, or the Florida Ridge. Kadyampakeni is the lead scientist for the research.
To contrast soil types in Florida, a third research site for the study will be at Southern Citrus Gardens in the southwest Florida Flatwoods region, Kadyampakeni said.
Kadyampakeni’s colleagues and collaborators, Evan Johnson and Yu Wang, are also based at the UF CREC site. Johnson, a research assistant scientist of plant pathology, will look at the citrus greening pathogen in the soil and tree roots. Johnson will evaluate root growth as a function of fertilization methods and rates. Wang, an assistant professor of food science, will evaluate nutrient concentrations in soil and plant tissues, using advanced analytical instruments.
“We will look at the impact of nutrients on root dynamics, yield and tree performance over time to measure the effects of nutrients. For example, we need to know if a foliar application gives a different response to the trees with HLB compared to a soil application,” Kadyampakeni said. “Nutrients are important for the defense of the tree.”
At the Indian River District, a region situated from Micco, in Brevard County, and south to Palm Beach County, is known for premier fresh grapefruit exported to points as far as Korea and Japan. There, three UF/IFAS scientists are at work to protect HLB-affected fresh fruit. Lorenzo Rossi, Rhuanito “Johnny” Ferrarezi and Alan Wright are at work with HLB-affected trees.
Rossi, assistant professor of plant root biology at the UF/IFAS Indian River Research and Education Center, will use a new technology camera to capture 2-dimensional images of tree roots, eliminating the need for traditional auger measurements that disturb the soil and root structure. The device is called a minirhizotron, and it scans roots below ground, inside a plastic sleeve.
“With the use of minirhizotrons, we can take pictures each month to see how fertigation, nutrients, and water impact root growth and dynamics,” Rossi said. “The images will show how the three variables impact production, fruit quality and HLB inside tree roots and leaves.”
The experiment will continue for three years. When all of the data sets are collected and analyzed, the research team will release Florida’s new guidelines for producing HLB-affected citrus with the best possible fertigation (irrigation with fertilization), root growth and overall root health, said Rossi.
“The project will look at how the HLB-affected trees uptake nutrients in the roots and translocate them to the leaves for the first time,” said Rossi.
Rossi works alongside Alan Wright, professor of soil and water science at IRREC. Wright assesses the role of fertilization on grapefruit tree growth and productivity.
“We will determine if current nutrient recommendations are still valid in the age of HLB disease,” said Wright.
Along with Rossi and Wright, assistant professor of Citrus Horticulture, Rhuanito “Johnny” Ferrarezi, will study how different in-ground fertilization methods — fertigation and controlled-release fertilizer – could increase tree performance at different rates, and fruit yield quality over time.
“The study is testing the effect of slow-release fertilizers and fertigation on ameliorating the HLB symptoms. The idea is to provide nutrients in small doses but more often to spoon-feed grapefruit trees and maintain fresh fruit yield,” said Ferrarezi.
Ferrarezi said his aim is to evaluate how nutrition could play a role in extending grapefruit tree life under HLB throughout the Indian River Citrus District. Kadyampakeni’s aim is to serve all of the state’s citrus producers with new guidelines in the era of HLB, an industry growers have sustained for more than 100 years.
“We want to reduce the impact of the bacterium that causes citrus greening, and we want to determine what foliar and soil applications will achieve this goal,” said Kadyampakeni. “Work to determine nutrients in healthy roots has never been done before because the trees were all healthy. Our findings will contribute new information that growers need to improve production.”