Agriculture and Parasitic Plants: How They Snag Hosts and Ruin Crops

In the war against parasitic plants that steal nutrients from other plants and reduce agricultural crops each year by billions of dollars, scientists at the University of Georgia may have scored a volley by learning what's behind those parasites' actions. They recently published their findings in the journal Science, noting that knowing how these plants detect and attack their hosts will likely lead to ways to control them.

Some plant seeds, for instance, like those of the invasive species Striga lutea, or Witchweed, can lie in soil for more than 10 years, waiting to grow until they are aware of a host nearby. "We wanted to understand how the parasites know other plants are nearby so we could develop new ways of combating them," said David Nelson, assistant professor of genetics at UGA, in a release.

Plants release hormones called strigolactones into the soil as their roots grow. Normally, they do this in order to establish a connection with fungi in the soil, to trade nutrients. But parasitic plant seeds can sense strigolactones--they then germinate, attach to the host root and draw nutrients from them, the release stated.

Surprisingly, the researchers have learned that the strigolactone detection system seems to have evolved from genes in the plant normally used to direct a seed's awareness of fire. When plants become aware of the smoke and ash from a forest fire leaching into the soil, they are signaled that because large, shady trees or ground cover is gone, they can more productively grow. The scientists recently learned that parasitic plants' evolution included a duplication of the smoke detector gene. In this case, some copies became strigolactone detectors, the release said.

Now that they've learned this, the researchers may be able to develop synthetic compounds that interfere with the parasites' strigolactone receptors. Or they could possibly create chemicals that copy strigolactones, which could be sprayed over a field before the regular growing season. Then the parasites would grow early and without hosts, which is called suicidal germination, according to the release.

The scientists' goal, ultimately, is to find an easy and affordable treatment that can be used in developing countries to increase food production, they said in the release.

"The process that parasitic plants use to sense their hosts has been a mystery in our field for more than 50 years," Nelson said in the release. "This could open the doors to a lot of useful new technologies to help those in greatest need."

More about Witchweed is on the USDA website, here.

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