Why are my Wheat Heads Dark?

There have been a number of reports of ripe canola looking black or, in some cases, sooty. We are hearing the same thing in wheat.  So what is the cause?

wheat melanism 005

Wheat affected by melanosis (photo by MAFRD’s Crop Diagnostic Lab)

Holly Derksen, MAFRD’s Field Crops Pathologist, recently did an interview with RealAgriculture.com on the topic of “Black Chaff, Melanosis, Glume Blotch: The Causes of Darkness on Wheat Heads at Harvest“.  Learn more by listening to Holly’s interview with Kelvin Heppner of Real Agriculture.com: http://www.realagriculture.com/2014/08/black-chaff-melanosis-glume-blotch-darkness-wheat-heads-harvest/

Submitted by:  Pam de Rocquigy, Provincial Cereal Crops Specialist, MAFRD

 

 

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Moving Beyond Purpling Leaves to Necrosis

There are reports coming from the Northwest Region of Manitoba (Grandview, Dauphin, Ste. Rose) where flag leaves on some wheat plants are turning a purple color, then bronze, and then becomes necrotic. In severe cases, the flag leaf has dropped off entirely.  Tissue samples have been sent into various labs with the diagnosis being physiological.  The good news is all the remaining leaves under the flag are in perfect condition

In an earlier post on Crop Chatter – Seeing Purpling Leaves in Wheat? – we reviewed the basics of why we see purpling plants.  However, in previous years we have seen that in severe cases, the flag leaf has become necrotic and sometimes dropped off, much like what is being reported in the Northwest.  Unfortunately, since it is physiological in nature, there isn’t much to be done. 

Of course, the next question is what will be the impact to yield if the flag leaf has become necrotic and/or dropped off.  In previous years when this has occurred, we haven’t heard any news of a significant yield reduction, which is good news.  However, we don’t have any firm data to say either way.   Everyone knows the importance of the flag leaf in yield determination, so one would expect there would be some impact. 

If we use the following table illustrating yield loss due to impact of rust on the flag leaf, we can see that the greater impact to yield occurs at flowering and when majority of the flag leaf is impacted.  As the crop matures the importance of the flag leaf diminishes as yield has largely been determined (with the exception of some kernel weight added during the grain filling process). This table is only a guideline however as yield loss is only estimated and growing conditions the remainder of the growing season will shape final yield.  As previously mentioned, all the remaining leaves on the affected plants are in perfect condition which will help with grain filling for the rest of the season.

Special thanks to Kathy for reporting what is happening in the Northwest Region!

Submitted by:  Pam de Rocquigny, MAFRI Cereal Crops Specialist

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Seeing Purpling Leaves / Stems in Wheat?

At a recent field tour, I was asked to explain why a particular spring wheat plant had a purple stem.

Over the past few years, Manitoba Agriculture’s Crop Diagnostic Lab and the Crop Industry Branch has received samples of wheat plants with a distinct purple coloration on its stems and in other cases, the leaves as well.  Similar symptoms were first reported in 2009 on leaves of KANE wheat (see photo below).  Since 2009, this purpling has been seen sporadically, usually on the leaves, and not only in KANE but also in the varieties of Unity VB, Glenn, AC Barrie, WR859 CL and Carberry.

Purpling of Leaves – cvr KANE
Photo taken by: A. Sirski (2009)

So what is the purpling?  Essentially it is a physiological response of the plant to abnormal stress conditions, such as low temperatures, drought, or a combination of hot and humid weather. Under stressful growing conditions, sugars can build up in the plant.  Within these sugars, there are purple anthocyanin pigments which then produces the color change.

It is also possible other plant parts such as stems (see photo below) and glumes can exhibit this purple coloration and in these cases it is called melanism (see Melanism in Wheat).

Purpling of Stems in Spring Wheat (2016) cropped

Purple Stems in Spring Wheat at MCVET Portage Site (Photo by P. de Rocquigny, 2016)

Purpling of leaves or melanism may be more prevalent in certain varieties as anthocyanin production can be a genetic.  It has been noted in literature the American varieties Amidon and Butte has exhibited this purpling.  Amidon is a parent of the variety McKenzie, which is a parent of KANE.  So this stress response of KANE that we starting seeing in 2009 and 2010 may be traceable back to Amidon.

Is there any impact to yield?  In the United States and here in Manitoba, this purpling has not caused any noticeable yield losses. However, keep in mind there could be other explanations to the color change.  If you think there could be more going on than just a physiological plant response, rule out phosphorous deficiency and viral diseases such as barley yellow dwarf that could also cause purpling of leaves or stems.

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture 

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Melanism in Wheat

The photo below is a sample of spring wheat, cvr Pasteur, from the Rivers area of Manitoba that shows symptoms of melanism.  Typicially just glumes are affected, but the symptoms of melanism can sometimes extend down the stem under the head.  In the photo, symptoms are evident on the glumes as well as a bit of the stem on two of the plants.  According to the APS wheat disease compendium,  melanism can occur due to genetics, as a response to a nonspecific stress, or copper deficiency and can occur on glumes, awns and/or stems.

 

Submitted by:  Pam de Rocquigny, Provincial Cereal Crops Specialist, Manitoba Agriculture

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