California Fruit and Vegetable

Tag: University of Florida Institute of Food and Agricultural Sciences

  • Oak Tree Mulch Study to Help Suppress Citrus Disease

    University of Florida Institute of Food & Agricultural Sciences – Florida citrus growers who face the most severe citrus disease in history notice how citrus trees under oak tree hammocks appear to tolerate the disease. Lukas Hallman believes oak trees may hold a compound that boosts the citrus trees’ ability to tolerate the disease.

    Hallman is a graduate student at the University of Florida Institute of Food and Agricultural Sciences Indian River Research and Education Center (UF/IFAS IRREC) in Fort Pierce, in the heart of the world’s premier grapefruit production region. The disease, Huanglongbing, or HLB, is caused by a bacterium and vectored by the invasive insect, the Asian citrus psyllid. Once infected, trees have a reduced fine root mass, yellowing of leaves, and smaller and bitter tasting fruit. In the U.S., the disease’s common name is citrus greening, said Hallman.

    “Anecdotal reports from Florida growers claim that citrus trees growing within the drip line of large oak trees have minimal HLB symptoms, while trees nearby, but not under the oak drip line, show severe symptoms,” said Hallman.

    Oak Extract was Medicinal During American Civil War 

    In his literature review of scientific journal articles, Hallman found that compounds from white oak tree bark were used as antimicrobials during the American Civil War. Marco Pitino, a former UF postdoctoral researcher, published the first research study for oak tree extract used in the greenhouse against the bacterium. The work took place at IRREC. Pitino found oak extract would improve citrus trees’ ability to tolerate HLB in the greenhouse.

    “The literature review and Pitino’s greenhouse study were enough to form a viable hypothesis for a field study with oak mulch beds under citrus trees,” Hallman said. “Pitino’s work took place in a greenhouse. His findings need field tests, and we need an answer to help the local industry, which has seen their crops drop by 90% in the last 15 years,” said Hallman.

    Lorenzo Rossi, assistant professor of plant root biology at IRREC, is Hallman’s graduate research advisor. Rossi persuaded Hallman to apply for a Southern Sustainable Agriculture Research and Education (SSARE) graduate student grant to fund research of his hypothesis.

    Southern Sustainable Agriculture Research & Education Grant

    When Hallman began to write the SSARE grant, a large oak tree fell on the IRREC property in a 2019 hurricane. With funds from a UF/IFAS Horticultural Sciences Department A.H. Krezdorn Memorial Fund, and collaboration with Robert Shatters, a research molecular biologist with the U.S. Department of Agriculture, Rossi and Hallman prepared the tree for mulch. The researchers used it for a bed under citrus trees in a research grove. With the research infrastructure in place, Hallman began to take monthly data from the root rhizosphere under the oak-mulched citrus tree beds.

    Rossi said Hallman’s grant application was successful, and in the fall of 2020, he began work to fulfill the project’s objectives. The SSARE grant provides more than $12,000 for the 2-year study to determine if oak mulch will suppress citrus greening in the open field.

    “The oak mulch is easier to apply to trees than the oak extract,” said Rossi. “Through the research, we may find oak mulch soil amendments improve the soil and that the compounds in the mulch help citrus trees tolerate HLB.”

    The project, “Deploying oak mulch to contain and suppress HLB disease in citrus,” has three objectives: to determine the capability of oak mulch to contain and suppress citrus greening, to measure the effect of oak mulch on HLB-affected citrus physiology, root growth and development, and to study the effect of oak mulch on microbial life biodiversity within the rhizosphere. Hallman carries out daily data collection for the project. Those tasks include soil samples, soil respiration, photosynthesis measurement, and nutrition studies.

    Graduate student Lukas Hallman distributes oak mulch on citrus tree beds.

    “With the SSARE project, we are able to expand the research,” said Rossi. “In the future, we will need to identify which compounds are beneficial, where those compounds are in the trees, which oak species hold the specific compounds, and how much of the right compounds will control the disease.”

    One year into the project, Hallman said he found more nutrients in the root rhizosphere. Also, preliminary findings show that as the mulch breaks down, soil biodiversity increases.

    “More nutrients are available to the trees as a result of the mulch breaking down into the soil,” said Hallman. “The nutrients are potassium and phosphorus. We have also found that mulch improves soil texture. Improved soil holds more moisture and requires less irrigation.” Soil that holds more moisture enhances plant root health and the trees’ nutrient uptake, resulting in more fruit and a longer life for the trees, Rossi said.

    “The research is a collaboration with the USDA,” said Rossi. “It confirms that UF/IFAS and the USDA are committed to the development of ‘an out-of-the-box’ cure for HLB.”

    Longterm outcomes for the research are to improve economic profitability for growers, to improve environmental health by reducing chemical inputs, and to support the surrounding community. In the years from 2006 until 2011, HLB took more than 6,500 jobs from Floridians. Oak mulch could help restore some of those positions, said Hallman.

  • In Story of Blueberries & Bees, Scientists Play Matchmaker

    Chew on this the next time you eat a blueberry: Every single blueberry is the result of a flower that was pollinated by a bee. 

    In other words: No buzz, no berry. With that in mind, it’s no wonder blueberry growers bring in hives of honey bees or bumble bees when their blueberry bushes are in flower.

    “We are big believers in pollination on blueberries. We believe pollination helps increase berry size and weight and increases the overall crop yield,” said Ryan Atwood, co-owner of H&A farms, which owns, leases and manages more than 350 acres of blueberries in north and central Florida.

    But pollinating blueberries with bees isn’t an exact science — yet. Successful pollination depends on a variety of factors, such as when beehives are introduced or how much buzz a blueberry flower needs to release its pollen.

    Moreover, blueberry growers across the United States report that ineffective pollination is a top concern for their business, as it directly affects the amount and quality of product they can bring to market, said Rachel Mallinger, an assistant professor in the UF/IFAS entomology and nematology department who specializes in pollinators.

    This is why Mallinger and several other researchers from blueberry growing states have teamed up to develop recommendations and tools to help growers optimize pollination.

    In addition to Mallinger, the research team includes scientists from Michigan State University, Oregon State University and Washington State University. Rufus Issacs, a professor in the department of entomology at Michigan State University, will lead the project, which is funded by a $2 million grant from the National Institute of Food and Agriculture, part of the U.S. Department of Agriculture.

    “Some years blueberry pollination goes well, other years not so much, so we are looking to help growers take some of the guesswork out of it,” Mallinger said. “Our ultimate goal is to provide a tool we’re calling the pollination planner. The pollination planner will help growers decide how many bees to use and when to bring them in based on their location, climate, size of their farm, and varieties of blueberry they grow.”

    Ebony Taylor, front, then an undergraduate student in the UF/IFAS College of Agricultural and Life Sciences, and Jon Elmquist, former lab manager in Mallinger’s lab, looking at flowers on blueberry bushes. Images were taken prior to national guidelines of face coverings and social distancing. Photo by Rachel Mallinger

    Mallinger and her research team will partner with Florida blueberry growers, including Atwood, to run their field experiments. The Florida blueberry industry is a $60 million-a-year business, and this research on pollination will help support this growing commodity.

    “This research will help us understand the economic benefits of honey bees for pollination and what number of hives are needed to properly pollinate,” Atwood said.

    The multi-state project has several components, Mallinger said.

    “Our contribution in Florida will be to look at our modern southern highbush blueberry varieties and determine their pollination needs and what makes them attractive to bees. Some varieties need to be pollinated with pollen from a different blueberry variety to achieve optimal yields, while others are more self-compatible. Some varieties may hold on to their pollen tightly, others less so. Even the color or size of the flower, or how much nectar it produces, might impact how attractive that flower is to a bee,” she said.

    Identifying those traits is just the first step, Mallinger added.

    “Blueberry breeders are usually trying to develop varieties that have good taste, resistance to pests, things like that. But we don’t think about how likely a blueberry variety is to be pollinated. If we can identify those traits that led to more pollination, we can inform breeding efforts,” she said.

    Other researchers on the project will develop recommendations for the number of bees — called stocking density — needed to pollinate modern varieties of blueberry. Another component of the project will investigate how weather conditions, such as extreme heat, influence pollination success. — By Samantha Murray, University of Florida Communications

  • Automated System Would Deliver Chemicals to Help Ward off Citrus Greening

    GAINESVILLE, Fla. — Imagine using a robotic arm to grip and puncture the trunk of a citrus tree to deliver chemicals into the vascular parts of the plant, reducing its susceptibility to the citrus greening disease.

    Ozgur Batuman, an assistant professor of plant pathology at the University of Florida Institute of Food and Agricultural Sciences, leads a team of researchers trying to make the automated delivery system a reality to help growers deal with the disease. Greening has led to huge losses for Florida’s multibillion dollar-a-year citrus industry.

    “The automated delivery system can be installed on any farm equipment and be operated by anyone who is driving – physically or remotely,” Batuman said. The person will be trained to use a joystick to control the arm that delivers the chemicals, he said.

    To conduct the research, scientists will use a $3.4 million grant from the National Institute of Food and Agriculture, an arm of the USDA.

    The system would extend from a tractor or ATV to grab the tree trunk. Because the grip has many small needles, it can create numerous tiny openings in the tree, said Batuman, a faculty member at the UF/IFAS Southwest Florida Research and Education Center in Immokalee, Florida.

     

    Psyllids Thumb

    Bactericides can enter the tree through those small openings, he said. These areas on the trunk with openings will be covered with a reservoir, such as a funnel or plastic balloon, that will hold the liquid containing the bactericide, Batuman said. The liquid then slowly enters through the holes of the trunk.

    This contrasts with traditional tree trunk injections, in which a grower would use large, single-needle syringes to inject liquid materials in one spot, Batuman said.

    Most bactericide treatments are not very effective at staving off citrus greening because they were not directly delivered into the citrus vascular system, where greening — and its associated bacterium, Candidatus Liberibacter asiaticus (CLas) lives, he said. The therapeutic chemicals can kill or suppress the growth of CLas and can be used in greening-affected plants, Batuman said. The system can also help newly planted trees fight greening by controlling the Asian citrus psyllid, which can transmit greening into citrus plants, he said.

    Researchers see the automated delivery system as part of an integrated pest management program to help stem the psyllid.

    “We are developing a delivery method that will send chemicals with therapeutic potential into phloem, where bacteria live,” Batuman said.

    This four-year project will also study citrus vascular systems with a multidisciplinary research team. Members of the team are
    , an associate professor of plant pathology; Amit Levy, an assistant professor of plant pathology; Ute Albrecht, an assistant professor of horticultural sciences; Fernando Alferez, an assistant professor of horticultural sciences; Yiannis Ampatzidis, an assistant professor of agricultural and biological engineering and Tara Wade, an assistant professor of food and resource economics – all with UF/IFAS. Also on the team are Louise Ferguson, an Extension specialist with the University of California-Davis and Veronica Ancona, an assistant professor of plant pathology at the Texas A&M University-Kingsville Citrus Center.

    By: Brad Buck, 352-294-3303, bradbuck@ufl.edu