Bacterial Blight Breakthrough

Bacterial Blight Breakthrough

Geranium growers all over the world may soon be sleeping more easily, thanks to a revolutionary new test to screen geranium and pelargonium species for Xanthomonas — the swift-moving bacterial blight that can wipe out an entire crop.

The work conducted by scientists at the University of Toledo (UT) in Toledo, Ohio, was funded through a USDA Agricultural Research Service cooperative agreement. Dr. Shulu Zhang of Louisiana State University managed the project while he was at UT’s Plant Science Research Center along with Dr. Stephen Goldman of UT and Dr. R.V. Sairam at Penn State University. Grower Bill Bettinger of Toledo also supported the project.

The scientists have developed a rapid, reliable test that is specific to 53 strains of Xanthomonas campestris pv. pelargonii (Xcp) but not to 46 other Xanthomonas species. Using Polymerase Chain Reaction (PCR) technology, the test detects a gene to signal the presence of XCP and then scores infection based on symptom severity. The test defines the presence of bacteria prior to the onset of symptoms and can assist in selecting resistant plants, which would have a negative PCR. A low PCR signal with mild symptoms would indicate disease tolerance.

This figure illustrates the detection of Xanthomonas campestris pv. pelargonii
(Xcp) using Xcp-specific PCR. The panel A in the top shows the healthy (left)
and infected (right) leaves of Pelargonium x hortorum plants. The panel B in
the bottom shows the presence (indicated by an arrow) of a 1.2 kbp
PCR product detected from the Xcp bacterial culture (left) and infected
plants (right) and separated through agarose gel electrophoresis and
visualized with ethidium bromide staining. The absence of the 1.2-kbp
fragment from the controls of Xcp culture medium alone or uninoculated
plants is also shown in this panel.

“Ideally, both the supplier and the receiving grower would profit enormously from a rapid, reliable test for Xcp,” Goldman says. “This test would allow the supplier to warrant that his material is free from infection prior to shipment, and the receiver to warrant that the material is likewise bacteria free upon receipt. The opportunity should be explored to use the availability of this technology to assist in breeding for resistance to Xanthomonas in geraniums.” The same technology may be used on other solanacea crops, like potatoes, he adds.

According to USDA’s Floriculture Crops Survey, geraniums represented $300 million in wholesale plant sales in 2006. Xcp is the most destructive disease for geraniums, especially zonal geraniums. “Typical losses resulting from blight have averaged between 10 and 15 percent,” Goldman says. “This number, however, to the greenhouse industry is deceptive. Infections are known to have run rampant in individual greenhouses and can cause up to 100 percent loss in geraniums.”

From the grower’s point of view, Bettinger says this revolutionary test is a godsend. He’s eager to make it available to growers. “It’s an incredible project that has been in the works for three years,” he says. “We’ve all lived through the repercussions of Xanthomonas. With bacterial diseases, you want to know before the guy down the street knows. Growers don’t sleep if the crop looks bacterial but they’re not sure. It’s so hard to confirm. You want to get eradication and need to know now. You can’t lay awake 10 days to two weeks waiting for test results. If we can get a system to test for bacterial problems that’s fast, growers can sleep at night.”

Both Goldman and Bettinger say geranium breeding companies have expressed interest in the technology. The next step is to get growers to try the test in their operations. “In order for the grower to determine whether the plant material he receives from his supplier is clean with respect to Xanthomonas infection, a sampling protocol needs to be developed and the grower confident that the material sent for testing will receive a definitive answer,” Goldman says. “In order to do this effectively, we will need grower participation in a voluntary sampling study.”

Interested in being part of the sampling study? Goldman and Bettinger are looking for geranium growers. Contact Stephen Goldman at 419-277-0290, stephen.goldman@utoledo.edu, or Bill Bettinger at 419-861-8608.

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