PURPLE COLOR OF CORN LEAF: Everything you need to know and whether there is any cause for concern

Have you noticed the purple color of the corn leaf appearing? What happened?

The appearance of purple color on the green parts of the plant (leaf and stem) occurs in conditions of inadequate plant nutrition with phosphorus and is one of the typical symptoms of phosphorus deficiency. It should be emphasized that phosphorus deficit is not only manifested in corn, but also in other plants, considering that phosphorus, together with nitrogen and potassium, is in the group of essential elements.

Redness of corn is a phenomenon that usually occurs when the plant is stressed due to cold conditions and can occur even with an adequate supply of phosphate in the soil. It is important to understand that most purple young corn seedlings do not affect yield. Make sure the ground conditions are suitable when doing field work. Soil compaction can exacerbate or be the root cause of corn reddening. If the purple pigment does not fade as temperatures rise, there may be another problem that needs your attention.

Why does the purple color of the corn leaf appear?

The purple color of the corn leaf occurs due to the increased synthesis of anthocyanins in conditions of phosphorus deficiency and has the effect of reducing the photosynthetic potential, and therefore the normal growth and development of plants. In addition to this, insufficient nutrition of plants with phosphorus results in weak development of the root system, which in conditions of even moderate drought is very unfavorable from the point of view of the water regime of plants, because the root is dominantly present in the surface layer of the soil, from where water is easily lost through evaporation. In addition, the weak development of the root system causes unfavorable conditions from the point of view of mineral nutrition of the plants, as well as the possibility of crop failure. All these problems can be solved by adequate plant nutrition, according to their phosphorus needs and the conditions prevailing in the soil.

Purple plants can be seen beyond the seedling stage due to various factors. Phosphorus deficiency may be evident from compacted or injured roots. Hard, dry soils that can lead to P deficiency symptoms or reduce the plant’s ability to metabolize photosynthetic sugars.
Ear shrinkage caused by drought or other factors can cause sugars that would be distributed in the developing grain to remain in the leaves and stem.

Stems damaged by insects, hail or wind can destroy the plant’s ability to redistribute sugars and cause the stem, husk or leaves to turn purple. Often, a broken leaf can become purple in color because the sugars cannot move beyond the fracture site.

What does the purple color of the leaf mean for the plant?

Purple corn seedlings are caused by pigment accumulation anthocyanin. The purple color of corn, but also of other crops and fruits, is therefore caused by the accumulation of anthocyanin pigment.

Purple grapes, red cabbage, plums, autumn leaves and other red-purple fruits and vegetables owe their color to anthocyanin. Corn plants can have varying degrees of purple color at any time during the growing season due to genetics, environmental stress, insect injury, nutrient deficiencies, hail and other factors.

Purple corn seedlings can be quite striking due to their purple color in the field. In most situations, the discoloration is cosmetic, diminishes over time, and the impact on potential yield is negligible. Longer-lasting purple coloring can also occur when plants are under stress or suffer root damage. Severity of stress or injury can reduce yield potential. Purpleing generally occurs early in the vegetative stages and the maize crop will appear normal at the V6 stage. Early season purpleing will rarely cause yield reduction as many studies have shown that purpleing is only on the outer layers of leaf cells. Therefore, the process of photosynthesis is not threatened.

Genetics, environmental stress, root injury, nutrient deficiencies, hail and other factors can cause anthocyanin pigment accumulation in tissues.

Purplishness usually decreases as environmental and growing conditions improve. There is minimal, if any, impact on yield potential unless there is prolonged stress or injury.

Causes of purple color in corn

Genetics: Some corn products, due to their genetic background, have increased anthocyanin levels and can be very purple as seedlings.

Phosphorus deficiency: Phosphorus (P) is an immobile nutrient and may be unavailable to seedling roots, especially when early growing conditions are cool and wet (Figure 1). Under these conditions, seedling root growth may be slow, extending the seedling’s time without P. In general, as environmental conditions improve, new root growth catches up with available P, and with P absorption, the purple color diminishes. Unless there is a true P deficiency in the field, there is generally little or no yield loss associated with seedling P deficiency.

It is important to consider soil pH as P becomes increasingly unavailable when the pH is below 5.5 and above 7.3. Plants growing in these pH conditions may have a purple color during the growing season. With limited P input, yield potential may be reduced.

Compacted land: Compacted soil can create an obstacle for seedling roots. This can be a result of planting in too wet soil which can cause the seed furrow to have a solid wall and bottom that seedling roots cannot penetrate to get water and P.

Compaction from tillage or wheeled traffic can also be a factor. The potential for yield reduction exists if seedlings are unable to establish an efficient and productive root system.

Povreda korena: Seedlings with roots damaged by insects such as white grubs and grape root rot or limited by fertilizer or chemical injury may turn purple due to inability to reach P (Figure 3). The longevity of the purple color and the degree of eventual reduction in yield potential depends on the degree of damage and the appearance of favorable conditions for root growth in the environment.

Cold temperatures: Cold temperatures (4.4 to 10°C) can reduce the plant’s ability to metabolize sugars produced by photosynthesis.3,4 This scenario can cause sugars to remain in the leaves instead of being redistributed throughout the plant. Some anthocyanin genes are induced by cold; therefore, cold temperatures can turn on these genes and cause purpura.

Disease: The purple color can be caused by diseases that affect the vascular system of the root or plant. Root diseases, if they don’t kill the seedling quickly, can cause a purple color as they try to grow under the stress of a reduced root system. Vascular diseases such as Stewart’s bacterial wilt, transmitted by flea feeding, can cause the plant to become stunted and turn purple.

How else does the purple color of the leaf occur and how to diagnose it?

Purple leaf sheath occurs when dust, pollen, and other material gets trapped behind the sheath and breaks down, causing the sheath to turn purple; however, the stem remains green. This is a cosmetic situation with no impact on yield potential (Figure 5).
The disease can cause the decay of leaf tissue and/or vascular tissue of the stem, which interrupt the movement of plant sugars.

Typically, purple corn leaves are automatically diagnosed as a phosphorus deficiency early in the spring. Although purple corn leaves are a symptom of phosphorus deficiency, this does not always mean that there is a phosphorus deficiency in the soil itself. It may be that plants cannot access phosphorus in the soil due to problems with the root system, excess moisture in the soil or low temperatures.

Phosphorus deficiency in corn causes purple leaves, starting from the oldest leaves (bottom to top). However, purple corn can still occur even in the absence of phosphorus deficiency.

During the process of photosynthesis, sugars are produced and stored in plant tissues. These sugars are then metabolized in the plant to create energy for growth and reproduction. When plant growth slows, for example during cold weather or when root growth is limited by compaction, the accumulation of photosynthates in plant tissues, especially anthocyanins, can give leaves a purple color. When there are large temperature swings with bright sunny days and cool nights, plants are more likely to turn purple.

Large differences in sugar and anthocyanin accumulation exist between hybrids, and this is often why you may see only one hybrid turning purple in a field with multiple crops on it.

FACTORS TO CONSIDER WHEN PURPLE LEAF DISCOLOR OF CORN APPEARS

• Limited root growth
• Soil compaction and lateral compaction of the seed trench
• Cold soils and ecologically cold conditions
• The level of phosphorus in the soil
• Genetics

ACTION PLAN:

Look for patterns in the field to determine if purple corn leaf color is due to phosphorus deficiency, compaction zones, areas of restricted root growth, or just genetic expression. If the purple color is limited to a specific area of ​​the field and is not associated with low or compacted areas, look further into the soil conditions.

• Put the plant in context: Was the weather cold but sunny?
• Test soil fertility to rule out phosphorus deficiency.
• Dig up plants to examine the root system: Is root growth limited by compaction or insect feeding?

Compaction of the SIDE WALLS

Lateral compaction inhibits root development, nutrient uptake, and slows overall plant growth, which can lead to purple discoloration. It is critical to ensure good seedbed preparation and seed drill settings to limit side compaction. Choosing the right closing wheel for soil conditions can reduce lateral compaction when planting.

Typically, there is not a phosphorus deficiency in the soil, but a problem with phosphorus availability. The leaves will turn green again when environmental conditions change and the plant returns to its normal growth cycle and redistributes sugars.

Source: BAYER, farmprogress