Seed & Chemical
Copper’s role in ergot formation and crop lodging
By Top Crop Manager
The pollination factor.
Wheat, barley and oats are all close-pollinated. In simple terms this means
that pollination leading to grain formation occurs before the flower opens.
Anthesis (protrusion) of the anthers occurs after fertilization has taken place:
pollination (fertilization) has already occurred. Naturally in the field, wheat,
barley and oats do Not cross pollinate. This is why cultivars of wheat, barley
or oats are grown side by side for seed. There is no cross-pollination in the
field. Bread wheats in the field do not cross with other wheats of any kind
(like durum or utility), even when grown side by side. Rye on the other hand
is a cross-pollinated cereal and certified rye crops grown for seed must be
planted miles away from any other rye crops.
Rye is highly susceptible to ergot infection, since its flowers open before
pollination has occurred. This allows ergot spores, either windborne or carried
by nectar and pollen-feeding insects, to infect the rye stigmas (the female
parts of the grain flower).
Research in the UK by R. E. Mantle and O. J. Swan has shown that it is not
a viable prospect to improve wheat or barley vigour and yield by growing male
sterile hybrids, as is the case with grain corn. What happens is that the male
sterile lines of cereals have to open their flowers prior to pollination and,
like rye, they become heavily infected with ergots and yields of male sterile
lines are less than 50 percent of the self-fertile checks.
So, if close-pollinated wheats, barley and oats exclude stray (outside) pollen,
how does ergot infection occur? The answer is quite simple, copper deficiency
results in pollen sterility and/or failure of pollen release. This fact was
established in France by Z. Azouaou and A. Souvre and confirmed by Dr. Robin
Graham in Australia in a published article in 1975. Consequently, normally closed
flowers of wheat, barley and oats, which fail to self-pollinate, open up to
allow their stigmas (female parts) to trap outside sources of pollen. This means
that wind and insect-borne ergot spores now have access to open cereal flowers
and ergot infection can occur. Failure to self-pollinate also means that cross-pollination
in these cereals can occur from windborne cereal pollen spores. Many of the
cereal flowers may get neither pollen nor ergot and are consequently sterile
and grains are now missing, resulting in partially filled heads.
A similar ergot situation occurred in Finland, and in recent years in Quebec,
where barley crops showed up with unusually low yields and high levels of ergot
infection. The problem was solved by P. Simojoki in 1981 and traced to severe
boron deficiency causing pollen tube failure: the pollen germinated, but the
tubes failed to reach the barley ovary (female part) and fertilization failure
occurred. Consequently, the barley failed to self-pollinate, the flowers opened
and became susceptible to ergot infection.
This work on the relationship of pollen sterility, ergot infection and yield
loss as a consequence of copper deficiency has been summed up by the famous
German plant physiologist, Horst Marschner. In his book, Mineral Nutrition
of Higher Plants (1998 – ISBN 0-12-473542-8 HB), Marschner states that
the main reason for pollen non-viability is copper deficiency. He also points
out that high nitrogen fertilizer application can accentuate copper deficiency
and consequently, negatively affect yield expectations.
In this test, Marschner writes that "Re-translocation of copper is closely
related to leaf senescence (aging) in all green plants." Since high nitrogen
delays senescence, it also retards copper re-translocation. Impaired re-translocation
of copper into new high nitrogen supply growth results in stem deformations
as a consequence of copper deficiency. In other words, the critical deficiency
of copper in the dry matter of the whole shoot required for maximum growth increases
with increasing nitrogen supply.
In a direct quote from this text, "Impaired lignification of cell walls
is the most typical anatomical change induced by copper deficiency in higher
plants. This gives rise to the characteristic distortion of young leaves, bending
and twisting of stems and an increase in the lodging susceptibility of cereals,
particularly in combination with a high nitrogen supply." The inhibition
of lignification (which leads to lodging) is related to the direct roles of
two copper enzymes in lignin biosynthesis. In lowered lignification scenarios,
phenolic compounds can accumulate, resulting in melanosis (brown pigmentation)
In the simplest of terms, what this means is that if growers are aiming for
high yields in cereal crops, they should pay close attention to soil available
copper levels to avoid yield loss, quality loss, delayed maturity and severe
crop lodging, primarily as a consequence of copper deficiency induced by high
nitrogen levels. Foliar or soil application of copper may be necessary to maximize
yield and grain quality.
The window of opportunity to correct a copper deficiency lasts until just before
heading. Visual symptoms are a sign that should be verified by a tissue test.
Small amounts of copper applied at this stage can have a huge influence on yield!
Talk to your Agri-Coach for more information about correcting suspected copper