New technique has potential

to protect citrus from HLB

Citrus greening, also called Huanglongbing (HLB), is devastating the citrus industry. Florida alone has experienced a 50 to 75 percent reduction in citrus production. There are no resistant varieties of citrus available and limited disease control measures.

Some scientists think it is possible that orange juice could one day become as expensive and rare as caviar. In an effort to prevent this, three plant pathologists at the University of California-Berkeley and United States Department of Agriculture conducted research into ways to boost citrus immunity and protect the valuable fruit against citrus greening.

Because the bacteria that causes citrus greening cannot be grown in a lab, scientists have to find novel ways to conduct experiments. The University of California-Berkeley/USDA team looked at many different strains of the bacteria that cause citrus greening to see if they could identify peptides (a compound of two or more amino acids) that would trigger immune responses.

"This was a long list, so we narrowed it down by selecting small peptides that were a bit different in their peptide sequence, which might imply that the bacterium had made those sequence changes so that they wouldn't be recognized by the plant immune system," explained Jennifer D. Lewis, group leader of the research team. "Then we further narrowed that list to peptides from strains that caused disease in citrus."

Through this research, they showed that two peptides could trigger immune responses in multiple plant species, including citrus. These peptides may play a role in preventing or reducing yield loss from citrus greening.

According to Lewis, "We thought it was particularly interesting that some of the peptides predicted to elicit a response, could actually trigger immune responses in multiple plant species. This suggests that the immune response to these peptides is conserved across species."

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IMMOKALEE, Fla. — University of Florida scientists are working toward establishing a new biological method that may help farmers control the insect that transmits the deadly greening disease into citrus trees. Greening is present in about 95 percent of the citrus trees in Florida, so by using a virus that may kill the insect, growers may be able to reduce the need for pesticides.

Instead of spraying insecticides, scientists hope to harness the natural enemies of the tiny Asian citrus psyllid to manage the invasive pest, said Ozgur Batuman, a plant pathologist at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.

Batuman is leading a UF/IFAS research team investigating viruses that live in the digestive system of the psyllid. They want to see whether any of them can weaken or kill the insect.

The psyllid transmits the bacterium responsible for greening by feeding on a citrus tree's new shoots and leaves.

UF/IFAS scientists are getting promising early results with this research. Their latest research suggests a natural process that would kill the insect or at least prevent greening from being transmitted to citrus trees.

“This invasive pest is now established throughout Florida's commercial groves, so growers use insecticide sprays that are potentially harmful for the environment as one of their primary tactics for fighting citrus greening,” Batuman said. “By reducing psyllid populations in their groves, growers hope to increase the quality of fruits and the productive lives of their trees by minimizing the number of times a tree is exposed to the greening pathogen.”

To arrive at their results, Batuman and his team spent two years collecting psyllids from commercial citrus groves in 22 central and south Florida counties – from Lake and Orange counties in the north  to Martin County in the southeast to Collier County in the southwest.

They identified viruses within the psyllids' bodies.

By using a test that amplifies DNA, scientists found five viruses in the guts of the psyllids they collected. They believe they can use those viruses to control the psyllids that live in the very groves from which scientists collected them.

With these experiments, for the first time, scientists have taken big strides toward identifying viruses associated with the Florida psyllids. They also now better understand the presence of those viruses in the psyllids. Asian citrus psyllids first arrived in southeast Florida in 1998.

“Future experiments will investigate how these viruses can be manipulated so that they may alter the pysllid's biology,” said Batuman. “We also need to find out how the viruses affect survival and transmission of the bacterium that causes citrus greening disease, also known as Huanglongbing, or HLB.”

“By understanding how the viruses interact with the psyllid biology, we may be able to understand how to better control the psyllids,” he said.

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By: Brad Buck, 813-757-2224, bradbuck@ufl.edu, 352-875-2641 (cell)

U of F article

Citrus greening disease, or Huanglongbing (HLB), is deadly, incurable, and the most significant threat to the citrus industry. Most HLB research focuses on the tree canopy, but scientists in California studied the impact of HLB on root systems. They recently published the first study to report on the response of two different varieties of citrus to the causal bacterium, 'Candidatus Liberibacter asiaticus' using metabolomics and microbiome technologies.

"Metabolomics is a cutting-edge field of study that provides snapshot information about the metabolism of living things," explains author Emily M. T. Padhi, "while microbiome studies provide valuable information about the microbial communities living in a particular ecological niche - some microbes are beneficial to the host, while others can be harmful."

Padhi and colleagues wanted to see how the root system of two varieties of citrus responded to HLB. They collected roots from healthy and infected Lisbon lemon and Washington Navel orange trees grown in greenhouses at the same time and under the same conditions.

They found that both varieties experienced a reduction in root sugars and amino acids when exposed to HLB. However, they also found differences. While the concentration of malic acid and quinic acid (two metabolites involved in plant defense) increased in the navel roots, they decreased in the lemon roots. They also found that the beneficial bacteria Burkholderia increased substantially in navel plants but not in lemons, which contradicts previous studies.

"Overall, this is the first study to compare two varieties of citrus using a combined metabolomics and microbiome approach and demonstrates that scion influences root microbial community composition and, to a lesser extent, the root metabolome."

There is evidence to suggest that the causal bacterium moves to the root system soon after a plant becomes infected. A key strategy for preserving the health of an infected tree is root system management and research on different responses to HLB may help devise new variety-specific preventative and treatment measures.

Red the whole study

MAGE: Images of the bulk root mass and sample leaves from healthy and 'Candidatus Liberibacter asiaticus' lemon and navel plants.

Credit: Emily M. T. Padhi, Nilesh Maharaj, Shin-Yi Lin, Darya O. Mishchuk, Elizabeth Chin, Kris Godfrey, Elizabeth Foster, Marylou Polek, Johan H. J. Leveau, and Carolyn M. Slupsky

UC IPM revised the weeds, nematodes, plant growth regulators, and diseases sections of the Citrus Pest Management Guidelines! Learn how to manage diseases like anthracnose, bacterial blast, bot gummosis, brown rot, dry root rot, phytophthora gummosis and many more! Check out the new huanglongbing and hyphoderma gummosis sections. Learn also how to increase fruit set & size and reduce fruit drop using the updated section on plant growth regulators. Citrus Pest Management Guidelines (PMG)

These guides can be especially helpful when trying to compare symptoms on fruit or leaves at different stages of plant growth when trying to figure out what the problem might be.  For example, under the "Year-Round IPM Program", you want to know what is causing is causing scarring on fruit during fruit development.  So you go to "Fruit Development", and scroll down to "Look for other pests and their damage to fruit", and boom, there's the page comparing damage to fruit by different insects.  Or you want to see disease symptoms, go to "Look for diseases that cause symptoms on fruit".  Yeah!!!

In addition, we've launched the entire Pest Management Guidelines in our new, mobile-friendly format