The rainy season, in combination with unusual low temperatures, are causing slow plant growth for all summer crops, including corn. Cold temperatures and saturated soils are not only affecting corn stands through uneven emergence and lack of uniformity, but are also causing a phenomenon in young corn seedlings known as “purple corn.”
In many cases when the purple color is identified in small corn plants, the first thought that comes to the mind of agronomists and producers is that this could be an indication of “phosphorus deficiency.” Phosphorus deficiency is also generally associated with stunted plants and thin stalks. Other potential causes of purple color can be hybrid-related, a buildup of sugars (sunny days/cold nights), and restricted root growth. Thus, the question becomes: What is the main factor affecting the plant color if the crop otherwise looks very healthy, uniform, and vigorous?
In recent years, purple coloring on corn seedlings has been documented in different environments under diverse management practices and hybrids. The color is coming from the expression of genes for anthocyanin pigment formation. Multiple genes govern the expression of this color, and certain “cold sensitive” genes react to low temperatures (40-50 degrees F). Therefore, low nighttime temperatures such as those we have experienced at times over the past several days/weeks will promote purpling in corn seedlings. This condition is only expressed up until the six-leaf (V6) stage. Producers do not need to worry about this phenomenon. As soon as the temperature warms up and plants grow rapidly, the purple color should disappear (after the six-leaf stage). If not, then consider taking a soil sample for potential phosphorous deficiency.
At this point, the purple color is simply the result of a small degree of cold temperature stress -- nothing severe. The plant is growing very slowly due to the cool weather (not related to the purple color), but good growth and development should resume after the temperatures go back to the normal for this time of year.
Will the yield be affected by this stress? Previous information collected by several researchers concluded that yield is not likely to be affected by this phenomenon. Still, it is always good to continue scouting your acres for early identification of any potential problem affecting your crops.
Figure 1. Purple coloration in corn at diverse growth stages -- a result of the expression of genes for anthocyanin pigment formation. A close-up look with a microscope reveals that the pigment is only present on the top layer of the leaf tissues, without affecting the chlorophyll. The purpling effects varied with the leaf position in the canopy, with no clear pattern. Photos by Ignacio Ciampitti, K-State Research and Extension.
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist