NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

June 17, 1999

Biotechnology Forging an Alliance of NDSU Scientists for Weed Management Research

Geneticists and weed scientists typically had little interaction in the past when it came to finding weed-management solutions, but biotechnology has forged an alliance where there was none before. At North Dakota State University that scientific alliance also involves biology to a greater extent.

"Weed science has gone from visual inspection of an entire plant down to inspecting genes, and in some cases, studying individual molecules," says Cal Messersmith, a professor in NDSU's Department of Plant Sciences. "The advancement of biotechnology has made this possible, and as a result, the time involved in testing for known inherited traits can be reduced from months to weeks—or even days. But of course, the more complex the inheritance, the less quickly progress comes."

As had been the case with plant breeders in the pre-biotechnology era, weed scientists spent most of their time in greenhouses and field plots, but they spent considerably less time in a laboratory understanding the whys and hows of weed development. Using the problem of herbicide resistance as an example, Messersmith says weed scientists are now relying more on lab-based genetic testing to find answers that offer solutions. In some cases, those solutions may lie in genes that confer a particular trait.

"If we understand how the herbicide resistance developed and where it occurs within a given plant, we can develop strategies," Messersmith adds.

Being able to develop flexible strategies is at the heart of an evolving three-pronged scientific approach to weed management at NDSU, explains George Kegode, NDSU's weed biologist. While weed scientists have expended considerable effort studying weed control—that is, killing weeds—researchers have spent less time studying how weed competition affects crop yields and even less time investigating weed biology, or how a weed acts on its own. Future research efforts will involve studies on biology, competition and control.

"We need to know what makes a weed successful," Kegode says. "Why do weeds keep coming back? Understanding this question is an evolving process."

And there are other questions weed biology can help answer. For example, why do weeds emerge when they do? If a weed's natural emergence pattern is altered, such as by early tillage, will it be less competitive with crops?

"With biology, you create a strategy, and the strategy may be different each year," Kegode says. "The goal is to develop evolving strategies that do not impact yield but do reduce herbicide rates and frequency of use, so a producer can say, `I used a smart strategy this year, and I made a little more money than last year.'"

Kegode expects the use of molecular markers will play a key role in identifying genes that confer herbicide resistance. He says most herbicide-resistant weeds are annuals and proliferate by seed production, so one strategy for battling a resistant plant is to limit its seed-producing capability.

Yet despite the potential biotechnology holds for the plant sciences, applying it to weed science involves a different set of challenges than those faced by plant breeders. Unlike plant breeders, weed scientists must apply biotechnology to highly variable wild populations, says Mike Christoffers, a geneticist and post-doctoral student at NDSU.

Adding to that challenge is the need to identify the specific nature of different herbicide-resistance genes within a weed species. Christoffers says, "Not all resistant wild oat is the same and not all resistant green foxtail is the same. Resistant plants may develop independently throughout a geographic region and perhaps even within one field. And plants with similar types of resistance may not be closely related."

Offering another example, Christoffers says kochia may be resistant to some sulfonylurea herbicides but not all herbicides with ALS-enzyme-inhibiting modes of action. The reason might be that different herbicides inhibit the ALS enzyme at different sites on the same enzyme.

"What leads to herbicide resistance may be only one difference in a plant's genetic code," Christoffers says. "That small a difference may make a plant resistant or not resistant to a particular herbicide."

Only through the use of genetic testing will researchers be able to observe the mutations responsible for herbicide resistance and other weed-management problems, Christoffers says. One genetic technique particularly useful to weed science is the polymerase chain reaction (PCR).

Polymerase is a class of enzymes that scientists use for reproducing DNA. After extracting DNA from plants, Christoffers selects strands of DNA to replicate, or clone, using PCR. He currently sends his clones to Iowa State University where a machine called an automated DNA sequencer reads the genetic code.

Christoffers concludes, "It's a long process to identify genes and to identify mutations within genes that are important to weed science, but once you know that a mutation or a particular gene sequence will give rise to a trait you're interested in, such as herbicide resistance, you can predict the trait based upon the code. So, the advantage of using genetics for identification is speed, volume and accuracy."

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Sources: Cal Messersmith (701) 231-8149, George Kegode (701) 231-6420 and Mike Christoffers (701) 231-1054

Editor: Dean Hulse (701) 231-6136