Newswise — Scientists have known for a long time that plants grow differently when they are spaced closer together than farther apart. Plants use phytochromes, a group of protein photoreceptors to sense different wavelengths. Chlorophyll absorbs more red light than far-red light, so environments with more chlorophyll (that is, with higher plant densities) have a lower red to far-red ratio (R:FR). This allows plants to change the way they grow even before they start shading each other.

Two scientists at the University of Wisconsin-Madison, Melinda Y. Markham and David E. Stoltenberg, conducted field experiments in 2005 and 2006 to determine the effects of early-season (prior to canopy closure) R:FR light environments on corn morphology and grain yield. The results were published in the January-February issue of Crop Science. Although this response has been studied in many plant species, it is not well understood under corn field conditions.

The researchers planted three experimental plots of corn, from low to high density, along with a control plot. At canopy closure, the ratio of red-far red light was highest in the low density plots. Each treatment density was then reduced to low density, in order to avoid confounding effects of shading. Across years, grain yield per plant in the treatments with the highest R:RF ratio was 1.5 and 2.0 times greater than in control and low treatments. Plants at lower densities tended to develop more tillers, or extra branching developing from lower nodes on the main stem.

The results suggest that a lower plant density will induce a physiological response in the corn to initiate tiller growth before the canopy closes and it is subjected to shading effects. Because tillers and cobs are close to ground level at the time of canopy closure, it is likely that a signal transduction pathway via one or more intermediate signals (such as a plant hormone) transmits the light wavelength information from leaves in the canopy to plant tissues closer to the ground.

The study demonstrates the importance of early-season light quality and its effects on corn productivity. Further research how the R:FR molecular pathway controls tiller and cob development may provide direction for increasing productivity of elite corn varieties. The study was funded in part by the College of Agricultural and Life Sciences, University of Wisconsin-Madison.

The full article is available for no charge for 30 days following the date of this summary. View the abstract at http://crop.scijournals.org/cgi/content/abstract/50/1/273

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