Researchers Focus In On Grape Disease
March 17, 2010 Researchers using photographic technology to watch a deadly bacteria breakdown cell walls in wine grape plants — an image that previously had not been witnessed.
“Basically, we’ve been interested in determining how the bacteria moves,” said Dr. B. Greg Cobb, Texas AgriLife Research plant physiologist in College Station. “How do they go from one part of the plant to another?”
The death of wine grape plants from Pierce’s Disease is a serious threat to wineries from Texas to California, Cobb said, and no one has been able to stop or reverse the effects of the bacteria that is injected into the vines by an insect known as the glassy-winged sharpshooter. The bacteria that causes Pierce’s Disease, Xylella fastidiosa, colonizes a plant over a period of time causing it to weaken and die.
Cobb and his team of researchers zeroed in on the “matchstick” effect of Pierce’s Disease. Plants suffering from the disease drop their leaves, but the petiole — or stem that connects a leaf to the vine — remains, resembling a matchstick. This occurs over the length of the vine no matter where the initial insect injection occurred, Cobb explained.
The xylem of a plant is like a pipe with a spring in it which transports nourishing water to various parts of the plant. The bacteria that causes Pierce’s Disease moves through the plant in this way.
The researchers focused the electron microscope at 100,000th of a millimeter along the pit membrane. The membrane normally blocks larger particles from passing through the pits that are located in the xylem, but high-level photographs show the bacteria breaking down the membrane in order to get through the plant.
Cobb said the study examined syrah and cabernet sauvignon plants because they have been known to be impacted by Pierce’s Disease. In the field, they selected leaves that were still viable but had some “scorching” or water stress which indicated the disease was present.
Water stress contributes to the death of the Pierce’s Disease-infected plant, he added, but it may not be the only factor.
With this information and the photographs to illustrate the process, Cobb’s team continues to study the disease in hopes of figuring out what could be done to help an infected plant live longer. The two-year research effort was supported by the U.S. Department of Agriculture-Animal and Plant Health Inspection Service. The study will be published in Botany.
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