in remote rural areas of the Eastern
Cape Province (former Transkei),
where subsistence farming is predominant. It has also been shown to cause
equine leukoencephalomalacia (hole
in the head syndrome in horses - a
sporadically occurring mycotoxicosis).
Due to their health impacts,
fumonisins are attracting global attention. More than 70 countries have established regulations on maximum
tolerable levels of fumonisins allowed
in food and feeds. Currently, the level
of fumonisins in maize is not legislated in South Africa, but contamination
of commercially produced maize grain
is regularly tested for by the South
African Grains Laboratory in Pretoria.
This information is publically available
through their website
(www.sagl.co.za).
The symptoms associated with Fusarium ear rot include cotton-like white/
grey to light pink fungal growth evident on individual or clusters of maize
kernels randomly distributed across
the maize ear (Photo 1). Additionally,
fungal growth within the kernel may
appear as white streaks across the top
of the kernel (known as “starburst”
symptom – Photo 2). Disease symptoms vary depending on the maize
genotype, environment and the disease severity. In many instances, fungal growth is associated with insect
(stalk borer) damage. It’s important to
note, though, that the presence of the
fungus is not always associated with
visible symptoms, yet the grain can be
contaminated with fumonisins.
A maize plant becomes infected with
Fusarium in several ways and at any
growth stage (Fig. 1). The fungus survives on maize debris, and spores in
the air or water cause infection when
they come into contact with maize
silks. Stem and ear damage caused by
insects or other means provide an additional entry point for the fungus,
while infection may also originate
from contaminated seed or through
the root system. Infection due to in-
Photo 1: Fusarium ear rot of maize characterised by white fungal
growth on individual or clusters of kernels and distributed randomly across the maize ear (photo courtesy of the late W.F.O
Marasas)
Photo 2: Internal kernel infection by Fusarium verticillioides expressed as white streaks across the top of infected maize kernels
(photos courtesy of M. Vermeulen and L.J. Rose)
sect vectors and direct invasion of
kernels through stress cracks is
also possible.
Maize cultivars differ in their susceptibility to Fusarium ear rot, but
fully resistant cultivars are not
available. Genetically modified
maize containing insecticidal proteins for the control of maize
stalk borers have been shown to
be less susceptible to the disease
(and less toxins), due to the absence of insect wounds. The disease can also be managed with
agronomic practices such as crop
rotation, proper fertilization,
good irrigation practices, appropriate plant population densities,
and early harvest. The control of
insects and pests is also very important. However, none of these
practices can completely prevent
or avoid F. verticillioides infection
and fumonisin contamination.
Research funded by the South
African Maize Trust is currently
focussed on the characterisation
of South African maize cultivars
and breeding material for resistance to Fusarium ear rot. Furthermore, research conducted at
the Department of Plant Pathology, Stellenbosch University in collaboration with the Agricultural
Research Council - Grain Crops
Institute, Potchefstroom is geared
toward the identification and understanding of resistance in maize
breeding lines. The planting of
resistant varieties, as part of an
integrated disease management
strategy, offers an effective disease management approach for
the production of high quality
maize crops.