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Januarie 2017
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Gibberella on maize,
sorghum and wheat
T
he three most important crops grown in South Africa are
maize, sorghum and wheat. These crops are essential food
sources (such as carbohydrates and vitamins) for humans
and animals. They are also important in industrial products
and therefore the cultivation of these crops are of eco-nomic impor-
tance. It assists in job creation, with export of products and helps to
generate international currency.
Unfortunately, these crops can be infected by fungal pathogens
that can influence the yield and also lead to economic losses. The
whole plant can be infected – which can lead to root-, crown-, stem-
and ear rot (maize), grain mould (sorghum) and head blight (wheat).
The fungal pathogens that most commonly occur on these crops
and can cause severe damage, belong to the genus
Fusarium
.
Recently in South Africa there has been an increase in the occur-
rence of the
Fusarium graminearum
species complex infection of
these three crops. The diseases caused by the
Fusarium gramine-
arum
species complex are also known as Gibberella rot.
Previously it was thought that the diseases were caused by
F. graminearum
s.s., but with recent molecular technology new
species were found. Up to date there have been 16 different fungal
species that occur in the
Fusarium graminearum
species complex.
Another reason why the
Fusarium graminearum
species complex
is important lies in the fact that these fungal pathogens can pro-
duce toxic products known as mycotoxins. The toxins that are
produced are nivalenol (NIV) and deoxynivalenol (DON). Each
fungal species in the
Fusarium graminearum
species complex can
either produce DON or NIV and some species can even produce
both toxins (
Table 1
).
It is possible that the health of people and animals can be nega-
tively influenced when heavily mycotoxin-contaminated food-
based products of maize, sorghum or wheat are ingested over a
long period of time. Up to date there has been no way to remove
mycotoxin from contaminated food crops and the best way to re-
duce or limit mycotoxins in food is to control
Fusarium graminearum
species complex.
The fungal pathogens occurring in the
Fusarium graminearum
species complex can also differ in virulence (degree to which
disease severity can occur), plant part specificity (some fungal
pathogens can only infect roots/crowns/stems or above ground
plant parts) and then some species display geographical specificity
(occur only in specific areas in South Africa).
Research information gathered will help producers to be more
aware of the
Fusarium graminearum
species complex occurring in
their fields, as well as how to better control and prevent the infection.
Symptoms
Maize
Studies found that the fungal pathogen most likely infecting maize
ears was
F. boothii
(
Table 2
), however,
F. graminearum
s.s. was
ON FARM LEVEL
Fusarium graminearum
species complex
Integrated pest control
ANEEN SCHOEMAN
and
SONIA-MARI GREYLING-JOUBERT,
ARC-Grain Crops Institute, Potchefstroom
FUSARIUM GRAMINEARUM
SPECIES COMPLEX
MYCOTOXINS
DEOXYNIVALENOL NIVALENOL
F. acacia-mearnsii
X
X
F. boothii
X
F. brasilicum
X
X
F. cortaderiae
X
X
F. graminearum
s.s.
X
X
F. meridionale
X
TABLE 1: IN SOUTH AFRICA, THERE ARE SIX
FUSARIUM GRAMINEARUM
SPECIES COMPLEXES THAT OCCUR ON CROPS AND EACH PRODUCE DIF-
FERENT MYCOTOXINS.
PROVINCES
(MAIZE)
FUSARIUM GRAMINEARUM
SPECIES COMPLEX
F. GRAMINEARUM
S.S.
F. BOOTHII* F. MERIDIONALE
KwaZulu-Natal
X
X (roots)
Gauteng
X
Mpumalanga
X
North West
X
Free State
X
X
TABLE 2: THE DISTRIBUTION OF THE
FUSARIUM GRAMINEARUM
SPECIES
COMPLEX ON MAIZE IN SOUTH AFRICA.
FUSARIUM BOOTHII
IS THE DOMINANT
FUSARIUM GRAMINEARUM
SPECIES COMPLEX ON MAIZE EARS.
*Indicates the most frequent occurring
Fusarium graminearum
species complexes specie
1:
Fusarium graminearum
species complex causing
Gibberella ear rot of maize.
1