Researchers from UW-Madison now have a better understanding of the genomic structure of late blight, a disease that is attacking tomato and potato crops in Wisconsin this year.

The studies eventually may result in the discovery of ways to stop the blight.

A large international effort to sequence the genome of the pathogen relied heavily upon UW-Madison scientists to map portions of the genome that are difficult to sequence using traditional methods. The Madison scientists used a technique called optical mapping to better describe long, repetitive sections of the genome, sections previously thought of as possibly void of genetic information.

But closer study of the repetitive portions of the blight genome - which account for about 75 percent of the genome - showed they are key to understanding how the blight attacks and destroys crops.

The repetitive DNA makes the late blight genome two and a half to four times larger than similar pathogens, according to the research. And those sections of repetitive DNA contain genes that are specialized for attacking plants. The genes change rapidly, scientists found, so that hosts such as tomatoes or potatoes have trouble developing resistance.

The optical mapping approach used by UW-Madison scientists allows geneticists to view the repeated DNA sequences in much greater detail. Optical mapping was invented by David Schwartz, a professor of chemistry and genetics at UW-Madison.

A better understanding of the repetitive DNA afforded by optical mapping may reveal weak links in the pathogen's offensive strategy, said researchers.

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