citrus

Now a part of the Molcular Plant Pathology Laboratory

Citrus Quarantine Facility

Yes, there are orange trees in Maryland!

History of the Facility

The Citrus Quarantine Facility was created in 1984. It has been funded by the USDA, the University of Florida, and the University of California. The facility is composed of a greenhouse and laboratory which are used to study diseases of citrus. It is located 1500Km (930mi) away from any known commercial citrus growing region. Cooperating scientists from Florida and California, as well as other countries around the world can conduct evaluations with plants which are maintained under similar conditions.
 We also work closely with the Quarantine Laboratory at Ft. Detrick Maryland in order to conduct tests with the insects that transmit the various pathogens, such as the Brown Citrus Aphid.

Research at the Facility

There are several collections of plants infected with different diseases of citrus located in the greenhouse. The primary disease we work with is Citrus Tristeza Virus (CTV). This virus causes severe stunting, dieback, small size fruit, and even death of trees. Millions of trees world-wide have died due to this disease. Testing isolates in various citrus cultivars helps us to categorize the isolates in the collection into bio-groups and to find mild strains which can be used to protect trees from becoming infected with a more severe strain.  

A comparison between a mild CTV strain (left)
a healthy plant (middle) and a severe CTV strain (right)

Development of rapid and sensitive DNA-based diagnostic methods to assist in plant quarantine and phytosanitary applications, specifically Citrus Tristeza Virus, Citrus Variegated Chlorosis, citrus canker, Huanglungbin (citrus greening), Citrus Yellow Mosaic Virus, Citrus Chlorotic Dwarf virus, and Angular Leaf Spot of strawberry.

Recent accomplishments

Citrus Canker

 Pathogen detection. A U.S. patent has been awarded for the development of improved detection methods for Xanthomonas axonopodis pv. citri, the causal agent of Citrus Bacterial Canker Disease. This assay has already been used to confirm outbreaks of this serious disease in Florida, Argentina and Australia. The PCR based assay for this pathogen developed in our laboratory is currently the most sensitive and best available.

 

Citrus Variegated Chlorosis

Xylella fastidiosa is a bacterium that causes citrus variegated chlorosis disease in Brazil and Pierce's disease of grapevines in the United States.

Symptoms of Citrus Variegated Chlorosis disease, caused by the Gram negative bacterium Xyllella fastidiosa, on a sweet orange tree. In addition to the bright chlorosis, the disease also causes stunting and dramatic yield losses.
 

Detection of the pathogen Xylella fastidiosa in single leaf petioles (upper half of gel) and in single insect vectors, Oncometopia nigricans. The bright bands on this agarose gel are DNA fragments specific to Xylella fastidiosa amplified by the Polymerase Chain Reaction. This is the most sensitive and specific assay available for this pathogen.

Because of the importance of the citrus variegated chlorosis disease, Xylella fastidiosa recently became the first plant pathogen to have the complete nucleotide sequence of its genome determined. The sequencing project was carried out in Brazil. We have also developed a diagnostic assay for this virus which can be used to protect the U.S. industry from this disease.

For more information about Citrus pathogens please contact Dr. John Hartung
For more information concerning growing citrus please contact Cristina Paul