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Scientists look at how nature makes a weed

In a lab, some 1,300 miles away from the nearest Mid-South rice field, a researcher works to learn what makes a weed a weed.

The work with red, or weedy, rice holds promise in the battle against invasive species and could help researchers develop better ways to deal with herbicide resistance.

While focusing on sequencing and comparing the genomes of cultivated rice and weedy rice, University of Massachusetts evolutionary geneticist Ana Caicedo hopes to learn how the weedy species evolved from a common domesticated ancestor.

“This will be the first approach to find genetic differences between weeds and cultivated species,” she says.

The research is part of a nearly $2.5 million effort funded by the National Science Foundation. It includes researchers in Arkansas as well.

Earlier work showed that the weedy rice in the U.S. likely descended from common cultivated groups. That fact alone, Caicedo says, makes it the “ideal model for understanding the genetic changes by which weediness emerged in agricultural settings.”

With the entire weedy rice genome sequenced, Caicedo will compare it to the cultivated rice and see where the genes are the most different. “We want to figure out what changes have to occur in order for it to behave like a weed,” she says. “Weedy rice is closely related to wild rice, so that makes us believe that it came from a cultivated ancestor.”

Studying shattering

Weeds separate from domesticated crops at several junctures. Shattering is one of the big ones for rice. Weedy rice shatters because it ripens at widely different times during the growing season, compared to the harvest ripening of cultivated rice. Caicedo has identified the genes she suspects are responsible for shattering; the catch is many strains of weedy rice have evolved over centuries.

“If we find the gene that’s controlling the shattering trait in rice, we would love to know if it was a mutation that led to the change. We want to know if weedy rice got the trait through hybridization or through mutation,” she says.

In the work, Caicedo is taking several approaches. One is to cross weedy and cultivated varieties and look at the great-great-great grandchildren. The farther out from the F1 cross, the more the traits get mixed up. “This is an approach to break up association of the traits and help us learn when a trait such as shattering entered the line,” she says.

Caicedo says while medical research is more advanced, research at the plant’s genetic level is the same as human medical mapping, regarding disease. “By discovering the genes that underlie the weedy traits and whether humans are to some extent causing evolution in weedy rice, we hope to come up with management strategies,” she says.

Caicedo, along with Univer-sity of Arkansas researcher Nilda Burgos, also is looking at samples from Clearfield rice fields “to find out whether the use of Clearfield herbicides is making the populations of weedy rice change. Was the weedy rice of 20 years ago different than that of today?”

“If we figure out that’s the case, then people more talented than I am will hopefully be able to come up with management strategies,” Caicedo says.

This article published in the June, 2011 edition of MID-SOUTH FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.