Purple
Corn! Why Does it Occur?
Purpling of corn plant tissue results from the formation of a reddish-purple
anthocyanin pigments that occur in the form of water-soluble cyanidin glucosides
or pelargonidin glucosides (Hak, 1998).
A hybrid's genetic makeup greatly
determines whether corn plants are able to produce anthocyanin. A hybrid may have
none, one, or many genes that can trigger production of anthocyanin. Purpling
can also appear in the silks, anthers and even coleoptile tips of a corn plant.
Well, you may say, that's fine but what triggers the production of the
anthocyanin in young corn at this time of year? The answer is not clearly understood,
but most agree that these pigments develop in young plants in direct response
to a number of stresses that limit the plants' ability to fully utilize the photosynthates
produced during the day. These stresses include cool night temperatures, root
restrictions, and water stress (both waterlogged and droughty conditions).
Figure 1. Moderately Purple Corn
Since the anthocyanin occurs in the form of a sugar-containing glucoside, the
availability of high concentrations of sugar in the leaves (photosynthesis during
bright, sunny days) further encourages the pigment formation. If fields are stressed
by other factors such as soil compaction, herbicide injury, disease damage, or
insect injury, the purpling becomes even more pronounced.
It has been
my experience that the combination of bright, sunny days and cool nights when
corn ranges from V3 to V6 in development (3- to 6-leaf collar stages) most commonly
results in plant purpling. Hybrids with more anthocyanin-producing genes will
purple more greatly than those with fewer "purpling" genes. In most
cases, the purpling will slowly disappear as temperatures warm and the plants
transition into the rapid growth phase (post-V6).
Figure
2. More Intensely Purple Plant
I have rarely diagnosed
phosphorus deficiency as the primary cause of purple plants early in the season.
Nonetheless, cold or wet soils inhibit root development and can aggravate a true
phosphorus deficiency situation, frequently causing even more intense leaf purpling.
What
About Yield Losses? Does the leaf purpling lead to yield losses later on?
The
cause of leaf purpling, not the purpling itself, will determine whether yield
loss will occur by harvest time.
If the main cause is the combination
of bright, sunny days and cool nights, then the purpling will disappear as the
plants develop further with no effects on yield. If the stress of restricted root
systems is a major contributor to the purpling, then the potential effects on
yield depend on whether the root restriction is temporary (e.g., cool temperatures
& wet soils) or more protracted (e.g., soil compaction, herbicide injury).
Plants can recover from temporary root restrictions with little to no
effect on yield. If the root stress lingers longer, the purpling may continue
for some time and some yield loss may result if the plants become stunted.
Related
References
Chalker-Scott, Linda. 1999. Environmental Significance of Anthocyanins
in Plant Stress Responses. Photochemistry and Photobiology 70(1): 1-9.
Christie, P.J., Alfenito, M.R., and Walbot, V. (1994). lmpact of low- temperature
stress on general phenylpropanoid and anthocyanin pathways: Enhancement of transcript
abundance and anthocyanin pigmentation in maize seedlings. Planta 194: 541-549.
Dixon, Richard A. and Nancy L. Paiva. 1995. Stress-lnduced Phenylpropanoid
Metabolism. The Plant Cell 7:1085-1097. American Society of Plant Physiologists.
[On-Line]. Available at http://www.plantcell.org/cgi/reprint/7/7/1085.
Kim, Jae Hak. 1998. Maize Anthocyanin Pathway. Pennsylvania State Univ. [On-Line].
Available at http://scripts.cac.psu.edu/courses/plphy/plphy597_hef1/mpath.html.
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