The bacterium Erwinia carotovora gets its name from carrots, the crop in which it was first isolated and named, but it affects many other vegetables, including potatoes, cucumbers, onions, tomatoes, lettuce, and even some ornamental plants like iris. The soil-dwelling microbe invades potatoes and other crops either in the field or in storage and causes afflicted tissue to become soft and watery and then turn slimy and foul-smelling.
Potatoes need protection from this pathogen because unavoidable damage from machinery and routine jostling and tumbling during harvest and handling creates wounds that allow the bacteria to enter and cause disease.
Genes that confer soft rot resistance in potato have been identified, but getting the genes turned on when tubers are damaged-the time they need protection the most-was the challenge. In lab experiments, wounding turned on the gene ubiquitin7, or ubi7, in tubers. Other ubiquitin genes were tested, but turned on in wounded and nonwounded tissue alike, even in leaves where protection is not needed. So the promotor portion of ubi7 was attached to an anti-rot gene in experimental potatoes to make the anti-rot gene more effective when tubers were damaged. In preliminary lab tests, slices of tubers with the ubi7-driven anti-rot genes had 85 to 96% less decay than those without this gene-promoter combination. Testing is continuing in the greenhouse and field under a cooperative research and development agreement between the USDA-ARS and Demeter BioTechnologies, Ltd. (Durham, NC).
Although testing so far has been limited to potatoes, other crops might also benefit from protection offered by Erwinia-resistance genes linked to the ubi7 gene's promoter.
Wood, M. 1998. Ubi7-new tool for potato breeders. Agricultural Research/January 1998, pp. 12-13.
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