Texas A&M AgriLife researchers have made a discovery that will help combat fastidious pathogens, which cost U.S. agriculture alone billions of dollars annually.
For the past few years, Kranthi Mandadi, Ph.D., a Texas A&M AgriLife Research scientist and associate professor in Texas A&M's Department of Plant Pathology and Microbiology, along with his colleagues, has been working on developing new biological technologies to fight fastidious or “unculturable” pathogens. Mandadi and members of his team are based at the Texas A&M AgriLife Research and Extension Center in Weslaco.
The results of their work, “Plant hairy roots enable high throughput identification of new antimicrobials against Candidatus Liberibacter spp.” were recently published in Nature Communications.
Fastidious plant diseases and their costs
Fastidious plant pathogens infect citrus, tomatoes, potatoes, grapes, peppers and other crops grown throughout Texas. Often transmitted by insect vectors, these disease agents cause billions of dollars of damage each year. The U.S. citrus industry alone would save $3 billion per year through control of just one of these diseases — citrus greening. Additionally, the fastidious pathogen that causes Pierce's Disease in grapes is the No.1 threat to the $1 billion wine industry in Texas.
“Currently, invasive fastidious pathogens are causing several major outbreaks in row crops, specialty crops and citrus, with immense costs to Texas and the U.S.,” said Juan Landivar, Ph.D., director of the AgriLife center at Weslaco, which has been involved in efforts to combat fastidious plant pathogens for many years.
Landivar said an expanded effort against fastidious plant diseases would protect the health of crops, environments, economies and people across the country.
A way to grow “unculturable” bacteria
Some plant pathogens can be grown as pure cultures in the laboratory in the presence of artificial nutrient solutions. Being able to culture disease agents in the lab facilitates their study by providing researchers with a reliable supply of experimental material. However, an estimated 99% of bacteria in the world are fastidious, or unable to grow outside their native environment.
“The greatest obstacle to understanding and controlling fastidious pathogens was the inability to cultivate them in a laboratory setting and to screen for lots of potential therapies,” said Leland “Sandy” Pierson, Ph.D., professor and head of Texas A&M's Department of Plant Pathology and Microbiology. “But Dr. Mandadi and his team have developed a breakthrough method as an alternative means to propagate fastidious bacteria. These bacteria are believed to be responsible for Huanglongbing, also known as citrus greening disease, and other insect-vectored diseases such as potato zebra chip and tomato vein greening disease.”
The breakthrough came in the form of the “hairy root” system. This technology utilizes the pathogen-infected host tissues to produce so-called hairy roots that can serve as biological vessels for the propagation of these pathogens in the laboratory.
“Classical microbiological techniques developed early in the 19th century cultured animal and mammalian viruses in host cells, tissues and embryonated eggs,” Mandadi said. “In a similar manner, we hypothesized that plant hairy roots could be suitable for propagating fastidious pathogens. And indeed, hairy roots supported the accumulation and growth of fastidious plant bacteria.”
Microbial hairy roots appear similar to normal root tissues that develop from the plant and mimic a bacterium's natural environment, he said. This allows the growth of the fastidious pathogens in controlled laboratory conditions.
Expedited screening for antimicrobial treatments
While microbial hairy root cultures are not traditional “pure” test tube cultures, they allow on-demand access to the fastidious bacterium in the laboratory. This enables the expedited screening of diverse antimicrobials like chemical inhibitors, immune modulators as well as gene/CRISPR-based therapies.
Other advantages are that hairy root cultures are easy to produce in the laboratory and can be maintained for several months to a year in laboratory growth chambers. Depending on the pathogen and the efficacy of screening, it is also at least four times faster than conventional screening methods, according to Sonia Irigoyen, Ph.D., and Manikandan Ramasamy, Ph.D., both AgriLife Research scientists and co-authors of the study.
In addition, the hairy root bioassays are scalable, so they can be used to pre-screen from a few to several hundred potential therapies simultaneously in a high-throughput manner. The microbial hairy root system can also be used to obtain mechanistic insights into antimicrobial function.
“Use of this technique has already led to the discovery of six new antimicrobial peptides with proven efficacy in plant materials,” Mandadi said. “These antimicrobials, either singly or in combination, could be used as near- and long-term therapies to control citrus greening, potato zebra chip and tomato vein greening diseases.”
Collaborators in the fight
“Typically, the type of breakthrough Dr. Mandadi and his team came up with is unusual for a university system off-campus center, as such centers usually have limited personnel and resources,” Landivar said. “Fortunately, the support we have received from the Texas A&M University System and other funding agencies and collaborators has helped make it possible for the Weslaco center to perform this world-class-level research.”
Besides a team of researchers at the Weslaco center, Mandadi collaborates with scientists at Texas A&M University, Texas A&M University Kingsville-Citrus Center, University of Florida, University of California System, and industry stakeholders including Citrus Research and Development Foundation, Texas Citrus Pest and Disease Management Corporation, Bayer and other entities.
Southern Gardens Citrus, a subsidiary of U.S. Sugar in Florida, has partnered with Texas A&M to commercialize the hairy root system as well as new therapies for application in the field.
Landivar also said funding from the U.S. Department of Agriculture National Institute of Food and Agriculture's Emergency Citrus Disease Research and Extension program, NIFA ECDRE, and support from the Foundation for Food and Agricultural Research and AgriLife Research's Insect-Vectored Disease Grant are making it possible to facilitate development of innovative technologies and discovery of therapies to combat diseases caused by fastidious bacteria.
To expand on his research, Mandadi recently partnered on a new project with Citrus Research and Development Foundation, Bayer, Southern Gardens Citrus, University of Florida and University of California-Davis. That project is funded by the NIFA ECDRE program. The overall goal is to bring together academics, growers and agrochemical industry to discover, develop and commercialize therapies for citrus greening disease.
Mandadi said use of the hairy root system has already been instrumental in finding several potential new treatments for citrus greening and potato zebra chip, as described in the Nature Communications article.
“We hope this technology can be further expanded to find even more therapies against current and emerging fastidious pathogens and, ultimately, with the support of industry, deploy them as field-ready products,” he said.
A recent Ventura County ACP-HLB Task Force sponsored webinar was held, the topics and speakers listed below The PDF's from the speakers are available online
Webinar Agenda 8-13-20
Welcome, and update on status of HLB in California:
Leslie Leavens, chair, Ventura County ACP-HLB Task Force.
Update on area-wide participation rates and CDFA buffer treatments:
Sandra Zwaal, Ventura County Grower Liaison
Final report on 2017-2020 ACP surveying project in Ventura County, and overview of Phase Two research:
Beth Grafton-Cardwell, IPM Specialist and Research Entomologist, University of California-Riverside, and Director of Lindcove Research and Extension Center (retired); and Monique Rivera, Assistant Extension Specialist, Department of Entomology, UC Riverside.
Final report on deployment of detection canines to scout Ventura County commercial groves for evidence of early HLB infection:
John Krist, CEO, Farm Bureau of Ventura County.
Implications of canine detection data for HLB management in Ventura County commercial citrus:
Neil McRoberts, western regional director, National Plant Diagnostic Network, and professor of plant pathology, UC Davis.
For more information, contact us by email at email@example.com.
Citrus greening disease, also called huanglongbing (HLB), is a bacterial infection of citrus trees that results in small, misshapen and sour fruits that are unsuitable for consumption. The disease ultimately kills the tree.
Because there is no cure, HLB is a major threat to the $10 billion citrus industry in Florida, where it was first detected in 2005,and to the $7 billion industry in California, where it appeared last year.
Researchers from the Boyce Thompson Institute (BTI), the U.S. Department of Agriculture Agricultural Research Service (USDA-ARS) and the University of Washington investigated a seemingly unlikely source of biocontrols for HLB: neuropeptides found in Asian citrus psyllids, the insect that carries the disease-causing bacterium Candidatus Liberibacter asiaticus (CLas), which it spreads while feeding on a tree's leaves and stems.
The research team, led by BTI faculty member Michelle Heck, published its findings on Feb. 10 in the Journal of Proteome Research.
Laura Fleites, a research associate in Heck's group at BTI, focused on neuropeptides because they function as hormones in hemipteran insects – a class that includes psyllids, aphids, whiteflies, shield bugs and other crop-plaguing species – to regulate growth, development and other biological functions.
“If we could develop an insecticide that is specific for Asian citrus psyllids based on one of the insect's own neuropeptides, then we could protect citrus trees from the insect that spreads CLas,” said Heck, a USDA-ARS research molecular biologist and an adjunct associate professor in the School of Integrative Plant Science, in the College of Agriculture and Life Sciences. “Citrus greening disease is devastating our citrus industry, and we need to develop new ways for our citrus growers to control it.”
Fleites and the team characterized the full array of peptides found in the psyllids and identified 122 potential neuropeptides. While promising, the findings offer only potential starting points for combatting HLB, because unmodified insect-derived neuropeptides are not suited for use as insecticides in the citrus grove.
To turn the findings into a usable product, the team is now part of a collaboration aimed at identifying the best psyllid-derived neuropeptide for development. The team will then stabilize the peptide and decide the optimum method for delivering the insecticidal molecule to citrus trees – whether as a spray, by engineering trees to make the peptides themselves, or by some other method.
For the study, Fleites developed new extraction and analysis methods other researchers could use in their investigations of insect peptides.
“Thanks to USDA support, I was able to develop techniques that enable the identification of small, functional insect peptides separately from their larger, inactive precursors,” Fleites said. “Because these techniques aren't specific to psyllids, they may be useful for identifying neuropeptides in other hemipteran insects to protect crop plants.”
Heck said this work shows how USDA grant programs can be used to fund everything from discovery to product development. The neuropeptide discovery was done in a study funded by the National Institute of Food and Agriculture; the translational research is being done under a grant from the Animal and Plant Health Inspection Service.
Funding for this work came from a USDA Specialty Crops Grant and from the USDA-ARS.
Michael J. Haas is a freelance writer for the Boyce Thompson Institute.
Asian citrus psyllids feed on a citrus tree. The psyllids deposit a bacterium in the sap that causes citrus greening disease, a scourge to the citrus industries in Florida and California, worth a combined $17 billion.
- Author: Elizabeth Grafton-Cardwell
The Asian Citrus Psyllid Distribution and Management Site provides you with a zoomable map to view psyllids, HLB, Psyllid Management areas, parasite releases and management information. But if you are on the go, and would like to simply see on your phone where HLB infected trees are in relation to your orchard, you can use the HLB Grower App. It's a web-based app found by entering ucanr.edu/hlbgrowerapp into your phone browser, which you can then bookmark for future reference. The HLBgrowerApp provides a zoomable map or address bar to locate your orchard. When you click on the location of the orchard, it creates a circle around that point on the map and tells you if the orchard is more than or less than 5 miles from a known HLB infection. It also provides you with a link to the voluntary grower response plan posted on the CitrusInsider website. The voluntary grower response plan talks about what you can do to intensify protection against psyllids and HLB as the disease approaches your region.
Scan for the HLB App:
This is the summary of a recent article by Allen Morris, a retired University of Florida Extension Economist
Even when a cure for HLB is implemented, unless something is done to stop the decline in orange juice consumption, the citrus-growing part of the industry will become too small to support the infrastructure of input suppliers, harvesters, grove caretakers, etc. necessary for it to function competitively. For example, assume that the lower prices from lower cost production get into the orange juice market evenly over the 2023–24 to 2031–32 nine-year period, reflecting the time required for fruit produced from new plantings of HLB-resistant trees to increasingly impact prices. Ten years after the first plantings, by 2031–32, only 58 million boxes of Florida oranges and no orange juice imports will be needed. In spite of an 11 percent increase in the orange juice market stimulated by the lower prices, the underlying rate of decline in orange juice consumption eliminated its benefit.
The three major orange juice brands will probably continue mainly as juice storing, blending and packaging operations, using orange juice imported primarily from Brazil and Mexico, but also using juice from the small declining volumes of Florida fruit still available to process. However, because of the high costs of processing small volumes of fruit in the large processing plants owned by the brands and the companies processing oranges for the Coca-Cola Company's Minute Maid and Simply brands, it is likely that one of the bulk processors may have an opportunity to process fruit for all three of the brands. This would reduce costs by processing all of the industry's remaining volumes of oranges in one plant, and thus allow that processor to continue to operate. The bulk processors, other than the ones storing and blending juice for the Coca-Cola Company's Minute Maid and Simply brands and the one which processes the remaining volumes of oranges, will soon have no economic reason to exist in Florida. Private labels' orange juice needs will be supplied by imports, primarily from Brazil and Mexico.
Because of the declining U.S. orange juice market, the brands will probably increase their focus on the European orange juice market, which, as was pointed out, is being positioned to grow. There will also probably be a proliferation of exotic juice blends like blueberry mango, pomegranate limeade, strawberry banana, watermelon, berry greens, etc. being introduced by the brands as they begin to position themselves away from citrus.
This conclusion doesn't have to happen. But it is likely to happen if something isn't done to restore the U.S. orange juice market to growth. One way to fund that is to partner with Citrus BR the way AIJN and the European orange buyers/packagers are doing. The U.S. orange juice market is second only to Europe in importance to Brazil as an export market for its orange juice. If approached, the Brazilians would probably be interested in working with the Florida Citrus Commission the way they are working with AIJN to restore growth to the U.S. orange juice market.
For the complete article, go to: