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Diagnosing the Fungus Among Us

by Linda Burcham

When Extension agents come across a sickly plant and they can’t easily determine what is wrong with it, one of the first places they turn to is the Plant Disease Clinic, part of the Department of Plant Pathology, Physiology, and Weed Science at Virginia Tech.

Mary Ann Hansen, instructor, and Elizabeth Bush, research associate, manage the clinic. In 2008, the clinic evaluated more than 1,500 samples from 99 Virginia Extension offices, helping growers and homeowners identify and control diseases attacking their plants. “We are a service laboratory for the Extension agents,” Hansen says. “We provide our diagnosis and recommendations to the agents, who then let their clients know what actions to take.”

Aside from the obvious benefit of saving a valuable crop or plant, accurate identification of plant diseases also plays a role in protecting the environment.
Hansen notes that about 40 percent of the samples they receive don’t have a disease problem. What people think is a disease may actually be the result of insects, environmental problems like drought, or even damage from chemical treatments. The correct diagnosis can help eliminate unnecessary or improper use of pesticides that end up impacting the environment and can result in unnecessary expense.

The clinic is a member of the National Plant Diagnostic Network, a collective of land-grant university plant disease diagnostic labs across the country that join forces to enhance national agricultural security by their ability to quickly detect new disease and pest problems.

Members of the network have access to an electronic mailing list they use to send out queries about disease symptoms that may have them stumped. The list came in handy last year when Hansen received a sample of freesia plants from a Virginia greenhouse operation.

The plants had damage that was unfamiliar to her. “It didn’t look like a virus,” Hansen notes. “It looked like damage from mites or thrips, but our insect identification lab confirmed there was no evidence of insects.” Hansen photographed the sample and sent it to the mailing list. One member suggested sending samples to a USDA lab that specializes in identifying certain freesia viruses. Surprisingly, the answer came back that the plants had freesia sneak virus, which had recently been discovered in Italy where the USDA researcher testing the samples was from. It was the first confirmation of the virus in the United States.

In 2007, the clinic expanded its capabilities with the addition of laboratory space and equipment that allow plant disease diagnosis by molecular techniques rather than traditional microscopy or culturing methods. “You can think of it as plant CSI,” explains Bush. “Now we can use sensitive DNA analysis to identify some plant diseases. We’ve always been able to identify most pathogens by culturing or using the microscope, but now we can extract the DNA from diseased plant tissue when simpler techniques don’t work, and make a molecular determination.”

The lab expansion was funded through an equipment grant from the Southern Plant Diagnostic Network and additional laboratory space in Price Hall was allocated by the College of Agriculture and Life Sciences. Bush notes that the lab is now certified by USDA’s Animal and Plant Health Inspection Service (APHIS) and recently received approval to perform diagnostic tests for Phytophthora ramorum.This pathogen has recently killed numerous oaks in California and Oregon and also infects many plants commonly sold through nurseries. In 2004, it was found at a retail garden center in Virginia. “Now that the clinic can test for this quarantine pathogen, Virginia nurseries will receive faster responses on suspect samples, and we can assist with nursery surveys to ensure Virginia plants are free of this potentially devastating pathogen,” Bush says.

What is the most unusual specimen Hansen and Bush have ever analyzed? It has to be a sample of vinyl siding that had small, sticky black spots on it. The diagnosis: artillery fungus – a wood-decay fungus that can grow in the mulch around houses. Artillery fungus earned its name by its ability to shoot spore masses into the air, where they can attach to vinyl siding.