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July 23, 2014

Unraveling origin of devastating kiwifruit bacterium (Image 1)

Boris Vinatzer, an associate professor in the Department of Plant Pathology, Physiology, and Weed Science at Virginia Techs College of Agriculture and Life Sciences, was one of the lead researchers in a study that used the latest DNA sequencing technology to trace a devastating pathogen back to its likely origin in China. The pathogen, Pseudomonas syringae pv. Actinidiae (Psa), is the cause of the deadly "kiwifruit canker" disease.

Kiwifruit canker has been threatening the worlds kiwifruit industry and destroying orchards in Europe, South America and New Zealand since 2008, causing hundreds of millions of dollars in economic losses. PSA causes a red or white bacterial slime to ooze out of the plants stem and branches. It can even cause the entire plant to wilt and die. In the 1980s, there was a similar disease outbreak in China and Japan, however, researchers were unsure until now whether it was caused by the same pathogen.

The study, led by Vinatzer and Giorgio Balestra of the University of Tuscia in Italy, is the first to pinpoint China as the bacterium's likely origin. "It was detective work," said Vinatzer. "By sequencing the DNA, we were able to link all the bacteria back to a strain in China and determine where it probably all began."

Using PSA bacteria samples taken from kiwifruit trees in China, Italy and Portugal, (they also analyzed some bacteria from New Zealand, which reported the disease in 2010), the team sequenced the entire DNA of the PSA bacteria.

Seeking to solve the mystery of the disease's origin, the team examined how the bacteria may have evolved from the same ancestor by comparing DNA from the different bacteria samples to each other. The researchers discovered that the bacteria from China, Europe and New Zealand were almost identical; however, one small difference in one region of the DNA linked the New Zealand outbreak to the Chinese bacteria. The researchers believe the bacterium was probably imported from China into Italy and from China into New Zealand independently.

"The first step in stopping the spread of aggressive bacteria like PSA is knowing where they come from and how they have spread," said Balestra. "Now that we have sequenced the DNA and found its likely origin, we can start to figure out ways to stop it and similar bacteria from doing so much damage in the future."

In addition to direct practical applications, the study could lead to new insights into the adaptation of bacterial plant pathogens to crops--an integral part of Vinatzers current research, funded by the National Science Foundation, and for research carried out by Balestras group on detection of bacterial pathogens, funded by the Italian Minister of Agriculture and Forestry Policy. (Date of Image: 2012) [See related image Here.]


Credit: Virginia Tech



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