Visit the University of Florida’sCitrus Research and Education Center at Lake Alfred, and you encounter a group of scientists running hard to catch up with citrus greening disease — Huanglongbing, also known as HLB — the exotic Asian bacteria that has infested trees throughout the state’s production areas.
Since Florida’s greening disease problem first appeared in Miami-Dade County in August 2005, researchers at the center have completely retooled their programs to focus on it.
“HLB now involves about 90 percent of the effort here,” says Jacqueline Burns, the center’s director. “Growers are depending on us to find a solution to the HLB disaster, and they have made a tremendous investment of their own money to help research move forward.”
All 31 scientists here were asked to determine how their work could contribute to defeating the disease.
“The question is, How can I use my expertise to help inform the project on HLB?” says Burns, whose academic specialty is in post-harvest citrus handling and mechanical harvesting.
“It’s difficult to quickly change research like that,” she says, “but our scientists have expertise in citrus and are applying what they know to the problem. We’ve done things like asking the ag engineer to think about how to develop sensing technology to help growers detect HLB in the field. We’ve asked the irrigation specialist to think about how to more efficiently apply, in a sustainable manner, the nutrients that help the trees deal with the bacteria.
“We’ve asked the food scientist who analyzes juice quality to look at how HLB affects juice and how it might be more efficiently blended to minimize the flavor impact. With the levels of infestation we’re seeing, down the road will we even have healthy juice to blend? HLB does affect taste, and we’re going to have to deal with it.”
Of course, many research projects have a more obvious tie to the disease.
“One of the biggest projectsdeals with the question of how to bring young trees into production in the midst of an endemic HLB infestation,” Burns says. “How do we quickly get young trees into production when they’re infested? That’s a major concern. If the trees get it in year one, then decline and go down in year three, the grower has wasted time and money. It’s a huge problem, to have growers planting only to end up throwing money down a hole.”
Since some growers now try to minimize the effects of greening disease with an intensive nutrient program, that concept gets a close look at Lake Alfred.
“What’s the most appropriate nutrient cocktail?” Burns asks. “Should we standardize that? I’d say, yes. The application of fertilizer should be informed by leaf, soil and water analysis so you can come up to a standard of what the tree needs rather than making assumptions about what will help the problem. Growers who just apply nutrients without doing that may waste money — they may apply too much of this or that, or even not enough of something else.”
In addition, scientists are trying to determine if the micronutrient cocktail approach is just a short-term solution.
“Trees on these enhanced nutrition programs are still productive and not declining,” she says, “but the reality is that they could go down at any time. How long can they make it even though they are infected with HLB? We’re looking at that, as well.”
Developing disease-resistant varieties is the long-term answer. Turning out new genetic lines cannot happen overnight, however. That means the scientists look at short-term, intermediate-term and long-term solutions for greening.
“The short-term approach focuses on pest control,”
she says. “How do we deal with the psyllid, the vector for the bacteria?
“A tremendous amount of work is being done on pesticides. We’re looking at how the psyllid feeds and how that informs the selection of pesticides. We’ve learned from other countries, like Brazil, that area-wide management programs are the only way to defeat the problem in citrus.
“The psyllid flies around. It moves, so it can be controlled much better on a large scale. The short-term solutions involve how to better control the pest and how to maintain productivity until we get a long-term solution.”
Using micronutrient cocktailsalso fits the short-term approach, Burns says.
“We are absolutely in line, step-by-step, with the growers on this. It’s good to boost the health of the trees, even though they’re infected, with macro- and micro-nutrients. It helps sustain production in the short term.
“The troubling thing is, are we just allowing inoculum to build up and stay out there? Even one psyllid can do some damage. Do we really want those psyllids moving around and doing their thing? What we’re doing with the nutrient program is a tradeoff. We’re boosting short-term productivity and trading that for a psyllid buildup.”
Plus, the enhanced nutrient program greatly increases costs, she says.
“On the 400 acres we manage here at the center, our production costs have gone from $1,000 an acre to $1,800. It isn’t uncommon to hear growers talking about per acre costs of $1,500 or $1,800. Yes, you’re maintaining the tree and keeping it in production — but that’s still a significant cost.”
Intermediate-term solutions attack the problem in a different manner.
“These involve a modified genetic solution, where we’re allowing trees to carry peptides to harbor the disease for a short period of time. It will allow healthy growth and kill the bacteria on the tree for a short time,” Burns says.
“We are also looking at an antibiotic treatment that will kill the bacteria. We’re making a significant effort to disrupt the bacteria — you name it, we’re trying it. We don’t have a lot of information on the interaction of the vector with the bacteria. In a perfect world we would look to rid the U.S. of the psyllid.”
Burns and her colleagues hope development of trees that are resistant or at least tolerant to the disease will provide long-term answers. But, that will take time.
“We can’t plant a tree and hope to get an answer in one or two years,” she says. When working with citrus genetics, scientists have to consider many things ranging from taste to shelf life, along with developing disease resistance. All that gets boiled to a tree we take for granted.
“Traditional breeding is off the tablebecause of the peculiar way citrus reproduces, so our focus is on non-traditional breeding. An answer may come from outside the citrus genome, but putting that into the tree is difficult to accomplish — it requires knowledge of the citrus genome. Identifying a characteristic is the easy part; the hard part is getting it into the plant.”
Even though a genetic answer to greening may be distant, Burns thinks it will one day be available.
“We believe we can introduce a tree targeted to resistance or tolerance. We have thousands of trees at various levels of research right now. We have to look at thousands to understand which ones are promising — and we do have promising materials.
“We are getting these plants out there. The challenge is that if we say this particular plant is the one we want to move forward with, and it has a bad characteristic in something like taste, that sets us back. Getting a tree to market requires another whole layer of costs and approvals.”
In the scientific world, the six years since greening was discovered in Florida represents a mere blink of an eye. Some of the most basic aspects of research on the disease still have not been conquered.
“Every day since the disease was foundin 2005, one of our scientists here at the center has been trying to culture this bacterium so we can work with it in the laboratory,” Burns says.
“He is yet to find a culture medium where it can reproduce. We can’t get it to live in a test tube — that has eluded us so far. It’s just an example of the things we have to learn to do in order to deal with the disease.”
Burns, who was named director of the center in August 2011, after a couple years serving as interim director, came here in 1987 with a Ph.D. from Penn State and undergraduate and master’s degrees from the University of Arkansas. As director, she oversees 225 employees and coordinates research with other research stations and state and federal agencies.
“Since HLB came along, it’s no longer us against them in a competition for grants and funding,” she says. “It’s all of us against this disease — we’re fighting for sustainability and the productivity of the industry, to continue doing what all of us involved with citrus love doing. The citrus industry needs that boost from finding solutions.
“We still have to maintain our core capabilities in disciplines like horticulture, engineering, agronomic principles, water relationships, and irrigation timing and scheduling,” Burns says. “We have to keep all those going in the face of the HLB disaster. We can’t push everything else aside, because we never know when some new disease or production situation is going to develop, and we need to be ready.”