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Use of mutant collections to
understand pathogenicity
in economically important fungi
P
lant-pathogenic fungi cause diseases to major crop plants
and threaten global food security. Virulence genetics
underlie these fungal diseases and plant host colonisation.
Therefore, genetic determinants are mostly to blame for the
onset of pathogenesis, crop failures and subsequent staple food
price hikes.
As such, pathogenicity studies can use collections of fungal strains
containing mutant genes to provide immense function-based infor-
mation regarding virulence genes of economically relevant fungi.
These fungal mutant collections can assist a search for potential
fungicidal targets and novel resistance genes through fungal effec-
tor search.
This article provides an updated assessment of the function-based
contribution of mutant collections, using
Magnaporthe oryzae
and
Fusarium graminearum
as pathogenic fungal models.
Fusarium graminearum
is a predominant pathogen of head scab or
Fusarium head blight in wheat and barley, and a cause of stalk and
ear rot infections in maize (
Photo 1
).
These crops are considered important South African crops, which
makes
F. graminearum
a relevant pathogen to study in this country.
Fusarium graminearum
also produces several important fungal
toxins, including commonly studied toxins, such as deoxynivalenol,
nivalenol and zearalenone. When released, these toxins are often
problematic for many reasons in that they accumulate post-harvest
and potentially contaminate food and feed, which in turn, present
a health hazard to animals and humans.
Therefore, studying genes which are associated with the synthesis
and release of these toxins will essentially lead to effective control
strategies against Fusarium head blight epidemics and associated
health impacts.
Fusarium graminearum
mutant collections are therefore a promis-
ing molecular genetics tool for the high-throughput discovery of
genes associated with mycotoxin production and regulation.
Magnaporthe oryzae
is a leading fungal pathogen of rice in Asia. Al-
though not largely known to infect crops in South Africa,
M. oryzae
has destroyed about 15 000 ha of wheat in Bangladesh, suggesting
that the underlying disease, called wheat blast, is likely to emerge in
wheat growing regions of South Africa in future.
This pathogen elaborates an asymptomatic infection phase, called
biotrophy, that allows it to grow and feed on living plant tissues
(
Figure 1
), and is also able to switch to the symptomatic phase called
necrotrophy.
Additionally,
M. oryzae
can secrete proteins called effectors, which,
in addition to interacting with plant resistant genes, can induce
host cell death. However, host cell death induced by fungal effectors
may be host-specific.
59
ON FARM LEVEL
Integrated pest control
Plant-pathogenic fungi / Crop failures
DR THABISO MOTAUNG,
ARC-Small Grain, Bethlehem
1: Wheat ears infected by Fusarium head blight (a) and Fusarium ear
(b) and stalk rot (c) infections in maize.
1b
1c
1a