Maize for Silage
Technical
Insight 343

UNDERSTANDING PURPLE MAIZE AND UNEVEN SEEDLING GROWTH

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When maize plants emerge, it's not uncommon for farmers to notice that their seedlings have a purplish tint or some uneven early growth. Seed merchants and Area Managers may get many phone calls each spring from worried maize growers wanting to know why.

However, when the purple colour disappears - usually after the plant's six-leaf stage - so do many farmers' concerns. Their ultimate goals, after all, are yield and harvestability; and current evidence shows purple seedling colour does not directly affect either.

Still, their concern about purple seedling colour is understandable. If there is something wrong, they want to know the cause of the problem. What causes maize to turn purple? Is it bad? Will it affect crop development or yield? What can I or should I do about it?

This article will discuss factors which can influence purpling in maize seedlings and explore another seedling condition; uneven early growth. It is important to remember that while both these conditions occur during the seedling stage in maize growth, they should not be linked together.

WHAT CAUSES PURPLE MAIZE?

Purple maize is not a new phenomenon. It has been observed over the years in many inbred and hybrid lines all over the world. Wild maize found growing in the cool mountain regions of Peru and Mexico is often purple.

Purple seedling colour results from the expression of genes for pigment formation; anthocyanin pigments. Several plants have similar genes. For example, red maples have red leaves in the spring, but other maple varieties have green leaves. Similarly, most cabbage is green, but there is also red cabbage. The differences between the varieties - maize, maple, or cabbage - include the genes for pigment production. That trait, along with other traits you do not see, is inherited in the hybrid or variety.

This cross section of maize leaf tissue illustrates the accumulation of anthocyanin pigments. Notice that the purple pigmentation is produced in the top layer of cells and does not affect the chlorophyll content in the plant.

Most of the maize hybrids grown in New Zealand contain five of eight genes required to produce the purple colour. The other three genes are present in certain hybrids, and some of these genes are cold sensitive. When exposed to cool temperatures, they induce purpling in the young plants. Night time air temperatures below 10°C when day temperatures are above 15°C often trigger purpling.

These temperature-sensitive genes are generally only expressed in seedlings prior to the six-leaf stage. This early plant development stage also coincides with the period most likely to have low temperatures. As a result it is likely that hybrids with the eight genes for pigment formation will produce some purple seedlings each spring.

Purple pigments can accumulate in mature plants as well, but pigmentation then results from the action of different genes. Maize breeders often use hybrids with the genes for purple leaves and husks as plot markers in yield tests.

RESEARCH SHOWS NO DIFFERENCE

Testing of maize plants that exhibit genetic purpling at the seedling stage has shown no evidence of adverse effects on metabolism, growth, chlorophyll production or yield.  Cold temperature stress which induces purpling, however, does affect early plant growth. Regardless of whether the maize is purple or green, cool temperatures slow growth. Researchers studying purple maize have observed no difference between cold stress effects associated with purple seedlings as compared to green seedlings. Hybrids that develop the purple pigment when exposed to cold temperatures have been found to contain as much chlorophyll (the green pigment) as hybrids that remain green when grown under the same cool conditions.

When breeding maize, researchers select inbreds and hybrids with important economic characteristics.  Genes for purpling are neither purposely bred into or out of new lines.

Some of today's most popular hybrids carry genes for purpling and routinely turn purple when exposed to cool temperatures at the seedling stage. Many of these hybrids are consistently high yielders.

Young maize plants that do turn purple grow out of the colouration after the six-leaf stage. The purpling does not affect plant population, growth or yield.

In breeding maize, researchers select those inbreds and hybrids with important economic characteristics. Genes for purpling are neither purposely bred into or out of new lines.

Young maize plants that purple will normally grow out of the colouration after the six-leaf stage. This can occur quickly if the weather warms up and the maize grows rapidly, or it can be slow if the weather remains cool, retarding both root and shoot growth in the seedling. The cool temperatures - not the purple pigment, cause slower growth.

Most occurrences of purple seedlings are the result of a combination of cool weather and the genes present in the plant. Your local Pioneer representative can tell you if your hybrid has a tendency to turn purple under cool conditions.

PHOSPHORUS DEFICIENCIES

Phosphorus deficiency symptoms have been characterised as an accumulation of purple pigments in leaves. Phosphorus level as determined by soil tests and an examination of the fertility programs used, may determine whether phosphorus is likely deficient. If sufficient levels of phosphorus are already present, adding extra phosphorus will not turn purple seedlings green.

How can growers tell the difference between genetic purpling and symptoms of phosphorus deficiency?

  • First, examine the colour of plants over the entire field. If the purple colour is uniform through the field, the cause is probably genetic.
  • If purpling is quite erratic, this may indicate that phosphorus is limiting to plants in those areas.
  • If plants are beyond the seedling stage (more than six to eight leaves) and purpling is observed, then phosphorus deficiency is likely.

 

STRESS AFFECTS EARLY GROWTH

Some of the same stress factors that can limit phosphorus availability can also cause uneven early growth. Both green and purple maize plants can exhibit uneven seedling development. There is little hard evidence to explain why uneven seedling growth occurs in the spring because so many environmental factors may be present.

Cool temperature stress is a factor, and this may interact with variable soil conditions, seed placement, compaction, fertiliser placement, and amounts of crop residue.

Uneven early growth can be caused by a variety of environmental and stress factors. Genetically purple maize and green maize are equally susceptible to stresses that cause uneven development.

Literally, each seedling has a unique environment for growth and as a result some unevenness in plant development will occur. As a maize grower, you should only be concerned when that uneven growth is abnormally great. Perhaps a management strategy is needed to minimise some of the stresses to which the seedlings are being subjected.

The most critical assessment of seedling stress is plant establishment. If plant population is reduced, yield potential may also have been reduced. If adequate plant populations are achieved, then most research data shows that early seedling growth has little influence on final yields.

Factors increasing stress on seedlings include:

  • Cold soils: Early planting increases the likelihood of cold temperatures during emergence and early seedling growth. Minimum tillage leaves more residues on the soil surface, thus insulating the soil and delaying its warming.
  • Tillage: Shifts in tillage systems may result in less uniform seedbeds. Greater variation exists in aeration, seed coverage, and perhaps planting depth. Compacted zones can influence soil moisture for germination and limit root growth and nutrient uptake.
  • Fertiliser placement: Current tillage trends result in less uniform fertiliser distribution in the root zone.
  • Pesticide application: Misapplication of pesticides including over-application, non-uniform application, and improper incorporation can also affect crop growth and performance. Take time to calibrate your chemical applications to comply with label recommendations.

The stresses we cannot control, such as weather conditions, are likely the most critical.  Whether too hot or cold, too wet or dry, the weather will rarely be ideal for plant growth.

SEEDLING APPEARANCE DOESN'T PREDICT PERFORMANCE

Farmers do need to monitor their crops during the seedling stage so that development can be observed and problems corrected before they become serious.

Purple seedlings do indicate cold stress, but be sure to assess the effects of cold stress in all your fields, not just those with purple seedlings. Remember, too, that seed establishment is the most critical seedling trait because plant population differences can affect final yield potential.

Maize plants are very resilient. They can withstand a great deal of early season stress and come back to grow and yield well. Seedling appearance generally does not affect final crop performance as long as there is an adequate plant population.

If the seedlings are purple, chances are it's simply a genetic trait that won't affect performance. If the cause is not genetic, then you may have an actual or induced phosphorus deficiency caused by stress.

If seedlings develop unevenly, remember that some of the same stress factors that inhibit phosphorus uptake by plants can also cause uneven early growth. These factors include temperature, soil type, tillage practices, compaction, moisture, fertility, insects, pesticides and hybrid.

Appearances can be deceiving. Get the facts. Know the hybrid characteristics and be aware of environmental stress factors that could affect seedling growth. Recognise all stress factors and understand their effects. Then, manage the controllable factors for best production. These measures will help ensure that your crop will reach its full potential at harvest time.



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Revised: June 2015
Expires: June 2018