27 / 44
25
January 2017
also isolated a few times (Table 2). In the stems and roots these two
species as well as
F. meridionale
were isolated (Table 2).
Visible fungal growth on a maize ear usually starts from the tip of
the ear and spreads down to the base of the ear. Ears are more
susceptible during grain filling stage and become less susceptible to
infection as the ear matures.
Insects and birds that feed on the mature grain can expose the ear
and make it more susceptible to infection of the fungal pathogen
through the wounds. The visual symptoms showed that the grain
turned a pinkish-red colour (
Photo 1
).
The discolouration affects the quality of the grain. Severely in-
fected maize ears will lead to the grain not being suitable for
food or feed. With stem rot there is usually the presence of leave
damage. Infected stems and roots also show a characteristic pink-
red discolouration when cut open. Severe stem- and root rots can
lead to plants lodging in the field and leading to lower yields.
Wheat
In South Africa there are six
Fusarium graminearum
species
complexes identified that infect wheat (
Table 3
). The fungal spores
that occur on the plant debris in the field will infect the wheat
rachis during flowering stage. A dark brown lesion becomes visible
on a single spikelet and then the disease spreads to the spikelets via
the rachis. The spikelets turn into a bleached colour and the tissue
dies (
Photo 2
).
It is also possible that the pink-red fungal growth can be seen on
the spikelets. The kernels will shrivel up and can also be cov-
ered with fungal growth (
Photo 3
). These kernels become light in
weight and can be blown out during the harvest process from the
harvester and leads to yield losses.
If these kernels are used in the new season, the seed will have
poor germination which will result in seedling wilt. It is also pos-
sible to observe brown discolouration at the base of the stem and
the rot will spread until the whole stem is rotten. This will lead to
weak stems and the plant will lodge as in the case of maize.
Sorghum
The three
Fusarium graminearum
species complexes that infect
sorghum in South Africa are
F. meridionale
,
F. acacia-mearnsii
and
F. cortaderiae
(
Table 4
).
The visual disease symptoms are quite difficult to identify and
then to assign to a specific pathogen. The reason is that the visu-
al symptoms are not as characteristic as on maize and wheat. The
grain mould discolouration can be pink, grey, white or even black
(
Photo 4
).
The stem rot symptoms are similar to stem rot of maize giving a
characteristic pink or even purple discolouration of the internal
stem tissue. Grain mould usually leads to loss of grain, severe
grain discolouration, a decrease of grain size and weight and re-
duced market and nutritional value.
Control measures
Maize, wheat and sorghum each will have its own set of manage-
ment strategies. Overall, achieving control of
Fusarium gramine-
arum
species complex is very challenging and in most cases
*Indicates the most frequent occurring
Fusarium graminearum
species complexes specie
PROVINCES
(WHEAT)
FUSARIUM GRAMINEARUM SPECIES COMPLEX
F. GRAMINE-
ARUM
S.S.*
F. BOOTHII
F. MERIDIONALE
F. ACACIA-
MEARNSII
F. CORTADE-
RIAE
F. BRASILICUM
KwaZulu-Natal
X
X
X
X
X
Limpopo
X
Mpumalanga
X
Northern Cape
X
X
X
North West
X
Free State
X
X
X
Western Cape
X
X
TABLE 3: THE DISTRIBUTION OF
FUSARIUM GRAMINEARUM
SPECIES COMPLEX IN WHEAT IN SOUTH AFRICA.
FUSARIUM GRAMINE-
ARUM
IS THE DOMINANT
FUSARIUM GRAMINEARUM
SPECIES COMPLEX THAT HAS BEEN ISOLATED FROM WHEAT.
2: The characteristic tan discolouration of head blight of wheat caused by the
Fusarium graminearum
species complex.
Photo: Gert van Coller
2