Figure 1. There are a few situations that can cause leaf purpling such as hybrid genetics or nutrient deficiency.
Yield loss due to leaf purpling is mostly dependent upon the cause behind the symptoms which can be compounded with other environmental factors.
Purpling of corn leaves is generally a result of the inability of a corn plant to take up adequate quantities of phosphorous OR due to the presence of unique gene(s) in specific hybrids that trigger production of reddish-purple anthocyanin pigments in young corn plant tissue (Figure 1). Optimal daily growing conditions normally result in production of high concentrations of sugar photosynthates within leaves. Typically, sugars would be metabolized overnight and redistributed to other parts of the developing roots and stems. Cool night temperatures or other biotic/abiotic stressors that inhibit root development can concentrate sugar levels in leaves. It is believed that since anthocyanin occurs in the form of a sugar, concentrations of other sugars can further promote anthocyanin production and cause excessive purpling.
Figure 2. “Purple corn syndrome” from the accumulation of anthocyanin in the leaves. Hybrid Specific Response
Most corn hybrids contain one or more genes responsible for anthocyanin pigment production which causes purpling of leaf tissue (Figure 2). Hybrids containing multiple cold sensitive anthocyanin genes can be more prone to leaf purpling when soil and air temperatures are low during early vegetative stages.1 Hybrids containing multiple genes responsible for purpling can also be more visible than other hybrids growing under the same field conditions. As affected corn plants begin to transition from small seminal/radicle root systems to larger and rapid growing nodal root systems, they are better able to reallocate sugars from leaf tissue to roots and begin to green up. Purpling caused by pigment producing genes usually occur uniformly across fields and only in specific hybrids, making it easy to distinguish from other causes.
Root Inhibition and Phosphorous Availability Influence on Leaf Purpling
Although some hybrids are more prone than others to leaf purpling at early growth stages, it can be a common symptom in any hybrid when the plants are unable to take up enough phosphorous (P). Although purpling of leaves is a symptom of low soil phosphorous levels, it can also be an indication that the plant is having difficulty extracting nutrients from soil with sufficient P levels due to other reasons. Purpling of leaves when soil phosphorous levels are sufficient is usually the result of one or more factors that slowed or stopped root development. There are a variety of environmental, management and pest related reasons that can impede root growth in the early vegetative stages, resulting in leaf purpling. Applying additional phosphorous to purple corn when soil test values are adequate will not likely result in additional yield.
Leaf Purpling Influence on Yield Potential
Yield loss due to leaf purpling is mostly dependent upon the driving cause behind the symptoms. Stress such as cool temperatures or wet soil conditions that result in slowed root development may be temporary, and as conditions improve, plants grow out of symptoms with little to no yield penalty. More persistent stress from things like compaction or herbicide injury may persist longer into the growing season and have potentially larger impacts on yield potential, depending on the original cause. Purpling caused by insufficient soil P levels can result in significant yield penalties and should be addressed with future nutrient management plans. Hybrids that are more prone to purpling will usually grow out of symptoms quickly as temperatures warm and nodal root systems begin to develop with little to no influence on yield potential.
Reference:
1 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.
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