Disease
Inputs/Production
Oktober 2013
38
How to manage Fusarium ear
rot and fumonisin production
DR BELINDA JANSE VAN RENSBURG, ARC-GRAIN
CROPS INSTITUTE, POTCHEFSTROOM
F. verticillioides
can cause ear, root and stalk
rot of maize and can lead to economic losses
due to yield loss and grain quality reduction
(
Photo 1
).
F. verticillioides
has the ability to produce
mycotoxins (myco = fungi and toxin =
poison) named fumonisins. The consumption
of maize contaminated with fumonisins
may cause mycotoxicosis in animals such
as leucoencephalomalacia in horses and
pulmonary oedema in swine.
Fumonisin infected maize has been statistically
associated with human oesophageal cancer
in South Africa, Northern Italy and Iran. A
strong correlation between the consumption
of fumonisin-contaminated tortillas and
neural-tube defects in humans in Mexico
has been reported in literature. The potential
carcinogenic risk of fumonisin B1 to humans
was evaluated and classified by the World
Health Organisation’s International Agency for
Research on Cancer (WHO-IARC) as “Group 2B
carcinogens” which means they are probably
carcinogenic to humans.
To date there are no legal limits set locally
for fumonisin levels and when necessary, we
refer to the guidelines of the Food and Drug
Administration (FDA) of the United States
of America which is set at 2 ppm for human
intake and 5 ppm for horses, pigs, rabbits and
pet animals.
Epidemiology
F. verticillioides
is more common in regions
with hot and dry growing conditions especially
before or during pollination.
F. verticillioides
grows well at temperatures above 26°C and
according to literature, the calculated optimal
temperature for growth is 31°C.
F. verticillioides
has a saprophytic as well as
pathogenic stage and may infect maize at
all stages of plant development, either via
the silk channel, infected seed, or wounds.
F. verticillioides
can be transmitted to
uninfected plants by inoculum from field stubble
or airborne conidia (micro- and macroconidia)
which are abundant in maize fields during a
growing season. The most commonly reported
method of kernel infection is through airborne
or water-splashed conidia that land on the silks.
Symptoms
Fusariumear rot symptoms can vary depending
on genotype, environment and disease
severity. One symptom type noted in the field
is the growth of white-pink cottony mould on
kernels alongside stalk borer channels. Similar
symptoms are often associated with other
insect or bird damage on ears.
F. verticillioides
can also infect individual (
Photo 2
) or groups
of kernels (
Photo 3
) scattered randomly on
the ear. Another symptom type is a pink
discolouration of undamaged kernels, but this
must not be confused with a slight pinking
of certain maize white hybrids where the
discolouration is superficial.
Control measures
The responses of cultivars tested by the
ARC-Grain Crops Institute (ARC-GCI) to date
to
F. verticillioides
infection over localities
and seasons, is inconsistent. This means that
adequate and reliable resistance is not available
to maize producers. Emphasis therefore, needs
Photo 1: Reduction in grain quality due to
F. verticillioides
infection.
Photo 2: Single maize kernel infected by
F. verticil-
lioides
.
