for National Geographic News
Scientists have now proved what gardeners suspected all along: Weeds really can sniff out tomato plants.
Seedlings from the parasitic plant called dodder track chemical aromas to locate their preferred host plants, a new study says.
"Sniffing" the air, the seedlings can even identify preferred tomato-plant hosts over less desirable ones such as wheat, researchers from Pennsylvania State University in University Park report in today's issue of the journal Science. (Related:"Weird Plants Taking Root in Everyday Gardens" [August 2003].)
"This is a pretty cool example of plants behaving in a way that people think only animals behave," ecologist Richard Karban told the journal. Karban, of the University of California, Davis, was not involved in the study.
Keen Sense of "Smell"
Dodders, or Cuscuta, are known by a variety of nicknames including strangleweed and witch's shoelaces. They rank among the U.S. Department of Agriculture's list of top ten weeds.
The pest costs tomato growers in California alone about four million dollars (U.S.) a year, experts say. It will attack carrots, onions, and alfalfa, among other crops (related photo: farmer weeding crops).
The morning glory relative has no real roots, and unlike most other plants, it cannot produce food through photosynthesis.
Instead, the spaghetti-like weed smothers its host plant, injecting syringe-like needles into stems and leaves to suck out water and nutrients.
"It's kind of like a leach," said study co-author Mark Mescher, a Penn State chemical ecologist.
Because dodder saplings have only a limited amount of food in their seeds, the saplings must quickly find a host plant or die.
Mescher, fellow Penn State chemical ecologist Consuelo de Moraes, and graduate student Justin Runyon suspected that the weeds found their marks using airborne chemical cues.
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