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.
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 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