Updated September 2009
URL: http://www.kingcorn.org/news/timeless/PurpleCorn.html
Prevalent Purple Plants Possibly Puzzle Producers
R.L. (Bob) Nielsen
Agronomy Dept., Purdue Univ.
West Lafayette, IN 47907-2054
Email address: rnielsen
at purdue.edu
s folks trickle back into the Chat ‘n Chew Café
after several weeks of intensive planting efforts, conversations are beginning
to drift toward the condition of the young crop. Some of the café’s regulars
are reporting that whole fields have taken on noticeable shades of red and
purple over the past week or so. Landlords and tenants alike are wondering
what on earth is wrong with these fields.
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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 (Kim, 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).
There’s no question that many cornfields throughout the state have suffered through wet soil conditions during the past several weeks. Furthermore, soil compaction (tillage- or planter-related) is more prevalent this year and that restricts the development of the initial root systems. The additional stresses imposed by recent relatively cool nights (upper 30's to low 40's) and several bright sunny days (high levels of visible and UV radiation) may be the final “triggers” that result in fields of pretty purple plants.
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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).
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.
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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. [URL accessed Sep 2009].
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. [URL accessed Sep 2009]. Editorial note: This link is for biochemistry fans!
Nielsen, R.L. (Bob). 2009. Reddish-Purple Corn Plants Late in the Season. Corny News Network, Purdue Univ. [online]. http://www.kingcorn.org/news/timeless/PurpleCorn2.html [URL accessed Sep 2009].
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