Agri Leader

New intel in greening war

JOHN BUCHANAN
Published: February 20, 2013

As Florida citrus growers battle the virulent disease huanglongbing, also known as HLB or "greening," the University of Florida Citrus Research and Education Center is leading the fight with aggressive research aimed at solving the problem.

Jude Grosser, a professor of citrus breeding and genetics at CREC's Lake Alfred facility, is heading up a trio of current initiatives.

Perhaps the most promising has been examination and development of new rootstocks.

"We've been looking at rootstocks we've either collected from around the world or developed," said Grosser, who made a presentation at the recent Florida Citrus Show. "And we've started to see differences in their response to greening in the frequency or severity of infection. Right now, as a result of our work to date, we have intermediate root stocks that we think will get infected at a much lower rate and that once they do get infected, will be infected less severely."

In addition, Grosser and his colleagues are working to develop new varieties of fruit that are more disease-tolerant or resistant, which in turn had led to a focus on genetic engineering.

Any one of the three areas of research could lead to a breakthrough, Grosser said.

"That's the reason why we're working on all three," he said. "We don't know yet where the ultimate solution is going to come from."

In the meantime, Grosser said, growers need to understand their relative exposure, based on the size and location of their operations.

"If a grower is in an area that largely consists of corporate farming, where there are large acreages, they can coordinate aerial sprays for control of the [disease]," he said. "Or they can follow the infected tree removal program and probably have a good chance of getting trees established and productive in that kind of environment."

However, he added, "If you are a small farmer in an area where your neighbor might not be doing anything and you have an abandoned grove across the street, then pulling the [diseased] trees to remove the infection from your groves might not benefit you all that much, because the [bacteria] from across the street can infect your grove."

As a short-term solution, some smaller growers are now relying on enhanced nutritional programs to try to maintain a viable level of productivity within their existing groves until a solution is found.

"Some growers are doing that successfully and others are not," Grosser said. "And a lot of that depends on the diligence of the individual grower and how much they're paying attention to what is working."

There is also growing interest in a new "advanced citrus production system" developed under the auspices of CREC.

"That means that the trees are going to be grown in a completely different way than they have traditionally," Grosser said. "Trees are grown at a higher density, using a root stock that has a dwarfing effect so you can have smaller trees that begin producing fruit a couple of years more quickly than normal. You're trying to push everything up in terms of getting a return and making money by shortening the growing rotation so you get money earlier in the cycle."

Instead of a traditional grove with 115 trees per acre, and having trees for 30 years, the new system accommodates as many as 800 trees per acre. "And you start making money in the second year and third year," Grosser said. "Then when the trees start to go out, you start removing them. And when you hit a certain point, you start all over again."

Grosser is now working on research designed to develop new rootstocks specifically intended for the accelerated growing program.

Orie Lee of Lee Groves in St. Cloud, has looked at the new program and decided not to pursue it. "It requires a level of commitment and management that I am not prepared to make," said Lee, who was inducted in the Florida Grower hall of Fame six years ago and is currently harvesting his 67th annual crop.

Lee said that the current greening crisis is the worst problem he has ever seen in his seven decades in the industry. So far, however, he has been lucky.

"Some of our trees have become infected," he said. "But so far, our yields have not been appreciably reduced. But the problem is progressing and it has increased our production costs significantly."

Lee is a strong supporter of Grosser's rootstock research. "We all need to support it," he said.

In the long term, he is hopeful that a solution to the greening threat can be found.