Oaks could help infected citrus trees

University of Florida study says oak tree extract has curative effects on leaves of trees infected with HLB


GAINSVILLE, Fla. – Native trees that once dominated the landscape of Tulare County may be part of the answer to protecting one of the county’s most profitable tree crops.

Research at the University of Florida Institute of Food and Agricultural Science’s (UF/IFAS) recently found that oak leaf extract has an inhibiting effect on the bacteria that causes huanglongbing (HLB), more commonly known as citrus greening for its decolorizing effect on the rinds of citrus fruit. The disease is fatal for citrus trees and is responsible for killing off 90% production of Florida’s most valuable crop

Lorenzo Rossi, assistant professor of plant root biology at the UF/IFAS Indian River Research and Education Center (IRREC), is working along side colleagues at the U.S. Department of Agriculture to develop management tactics for production of fruit on trees affected by HLB. The research involves experimenting with irrigation and plant nutrition remedies to help HLB-affected trees tolerate the disease and extend their production years. These projects are funded by the Citrus Research Development Foundation and the USDA.

One of the findings of the research is that citrus leaves treated with oak leaf extracts showed a decrease in the presence of bacteria. The HLB-affected citrus plants treated with oak leaf extract were better able to uptake nutrients than were the citrus plants treated with only water.

“This study suggests that oak leaf extract will provide a new management treatment program to protect trees that have HLB,” said Rossi. “We will continue to develop a protocol for growers to produce our high-value citrus crops and to reduce the symptoms of HLB on the trees.

Other research results were increased chlorophyll content and plant nutrition. The scientists’ work appears in this month’s issue of Plant Physiology and Biochemistry, an internationally prominent science journal.

Marco Pitino and Robert Shatters with the USDA’s Horticultural Agricultural Service in Fort Pierce, along with Rossi, were responsible for design of the experiment and preparation of the manuscript. Liliana Cano, a plant pathologists with UF/IFAS, and Kasie Sturgeon, Christina Dorado and John Manthey were responsible for planning, conducting the experiment, and analysis of data and preparation of the manuscript. Rossi’s co-workers who study citrus horticulture and hydrology developed water and nutrition management practices.

“Research scientists work with a sense of urgency to contain the pathogen and to manage HLB’s impact on our important crop,” said Rossi, who works in Fort Pierce, at the center of the Indian River District. The district is known for its peerless grapefruit quality. For several years, growers across the state have noted that citrus trees that stood under oak tree canopies, or alongside oak trees, are healthy. However, grapefruit trees in a row or two away from the oak trees showed signs of HLB.

HLB oringinated in Asia, and more specifically from Japan to southern China and from Southeast Asia to India and Pakistan. HLB wasn’t detected in the Western Hemisphere until 2004 when it was reported in Brazil. HLB was detected for the first time in the United States, in Florida in 2015. The disease was first identified in Citrus Heights near Los Angeles in 2008.

A 2018 study conducted by the Visalia-based Citrus Research Board stated a potential 20 percent reduction in California citrus acreage due to the HLB could cost California 7,350 jobs, $127 million in associated employment income, and could reduce California’s GDP by $501 million in direct, indirect and induced impacts.

For the 2016-2017 marketing year, California citrus production valued $3.4 billion. The total economic impact of the citrus industry on California’s economy in 2016-2017 was $7.1 billion. Tulare County represents almost one-third of the total production value of the state’s citrus industry.

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