For velvetleaf in proximity to corn, “growing like a weed” means making additional demands on genes needed to fuel rapid growth in the race for sunlight and nutrients.
That’s one key finding in studies that evaluated velvetleaf growing in a monoculture or in competition with corn. Weed scientists found that when competing with corn, velvetleaf ramps up genes needed for assimilating carbon into sugars, genes used in photosynthesis and genes that stimulate cell division. In addition, genes that regulate the shade response that causes a plant to lengthen or elongate its stem are expressed in greater level in the weeds competing with corn than in velvetleaf growing alone.
“In other words, if you think the weed is growing more quickly than the corn, that may be because — as this research suggests — it is,” South Dakota State University weed scientist Sharon Clay said.
That study won a prestigious award for Clay and her co-authors, USDA-ARS scientist David Horvath and Danny Llewellyn, the sub-program leader of genomics and plant development at the Commonwealth Scientific and Industrial Research Organization in Australia. The scientists used technology called a DNA microarray analysis to study what genes were more actively expressed under different treatments in order to better understand how the weed’s basic growth functions were responding to competition from corn.
Better understanding of what is happening within the weed plant could lead to better weed control strategies to help farmers, Clay said — especially for post-emergent weed management.
“We don’t know, at present, exactly when these genes ramp up, but control should be applied prior to these events, because once this occurs, these plant modifications will accelerate growth rates,” Clay said. “Higher growth rates will result in larger plants more quickly, and those weeds are more difficult to control.”
Clay carried out the field plot research on velvetleaf grown in competition with corn in SDSU test plots near Aurora, S.D. Velvetleaf, like cotton, is a member of the Malvaceae family. A broad-leafed annual weed that is native to China and India, it was originally introduced to the United States before the 1700s as a possible fiber crop. The weed has spread worldwide and, if allowed to grow unchecked, can cause yield losses of 100 percent.
This study marked several first-time experimental achievements, including examination of gene activation through microarray analysis in the weed genome in response to competition with a crop. It also used DNA microarrays developed from a related plant — cotton, or Gossypium hirsutum — to carry out the study rather than using DNA microarrays specifically developed for velvetleaf.
These techniques were so innovative that the Weed Science Society of America gave Clay and her co-authors the society’s award for Outstanding Paper. Their study, “Heterologous Hybridization of Cotton Microarrays with Velvetleaf Reveals Physiological Responses Due to Corn Competition,” appeared in Weed Science in the November/December 2007 issue. The award is given to authors of the academic paper judged to be the outstanding contribution to the journal Weed Science over the past year. Only one paper is selected for the award annually.
“Although a picture is emerging concerning how corn responds to velvetleaf competition, significantly less is known about what effect the corn has on velvetleaf,” Clay said. In fact, in a related study by Clay and her colleagues that examined how corn responded to velvetleaf, researchers found that the corn actually slowed some of the same genes that velvetleaf accelerated.
“This seems to indicate that corn is a poor competitor with weeds, and while velvetleaf is speeding up growth in response to corn, corn may actually be slowing growth,” Clay said.
That has implications for weed management and may help explain why corn yield potential may be reduced by weeds even if controlled very early in the season — even when water or nutrients are not limiting.
“These data are just beginning to shed light on how different plants function,” Clay said. “But it would appear that there’s sound science behind the phrase, ‘growing like a weed.’ At least from what we can tell from studying velvetleaf growing with corn, weeds really do turn up the expression of genes that give them a competitive advantage.”
Clay and her colleagues are continuing to study crop/weed competition with research grants from several sources including the Agriculture and Food Research Initiative, the South Dakota Corn Utilization Council, and the South Dakota Agricultural Experiment Station.
Founded in 1881, South Dakota State University is the state’s Morrill Act land-grant institution as well as its largest, most comprehensive school of higher education. SDSU confers degrees from eight different colleges representing more than 200 majors, minors and options. The institution also offers 23 master’s degree programs and 12 Ph.D. programs.
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