Agriculture Reference
In-Depth Information
infected plant nears maturity, the glumes and
nodes become symptomatic.
are heavy and lesions coalesce. Pseudothecia can
survive saprophytically on wheat residue and
produce ascospores to infect subsequent wheat
crops (Scott et al., 1988; Hunter et al., 1999;
Hoorne et al., 2002; Eriksen and Munk 2003).
Ascospores are primarily windblown and can
serve as primary inoculum (Shaw and Royle
1989). The anamorphic stage of the fungus is
referred to as
Septoria tritici
Desm. Conidia are
produced in and around pycnidia and are spread
by splashing rain within the wheat canopy.
Conidia serve as the repeating stage of the fungus
during the growing season.
Distribution and losses
Stagonospora nodorum blotch is distributed
worldwide, particularly in areas prone to warm,
humid, and wet conditions during the growing
season (Eyal et al., 1987). The disease reduces
grain yield, grain weight, and grain quality (Eyal
et al., 1987; McKendry et al., 1995). Yield losses
up to 50% have been reported (King et al., 1983;
Eyal et al., 1987; Bhathal et al., 2003).
Pathogen variability
In the US, Adhikari et al. (2008) showed that
sexual reproduction was common in
Phaeosphae-
ria nodorum
in both spring wheat and winter
wheat growing areas. Moreover, they showed
that
Phaeosphaeria nodorum
populations could
be genetically differentiated from separate geo-
graphic locations. Differences in aggressive-
ness among
Stagonospora nodorum
isolates have
been found (Ali and Adhikari 2008). Host-
selective toxins have been found to be produced
by
S. nodorum
that are important in disease
development and determination of virulence
(Liu et al., 2004; Friesen et al., 2008). The
frequency of occurrence of
Phaeosphaeria nodorum
pseudothecia indicates ample possibility for the
fungus to recombine (Cowger and Silva-Rojas
2006).
Identifi cation and symptomology
Septoria leaf blotch is also known as wheat leaf
blotch and speckled leaf blotch. Symptoms often
appear in the lower leaves of tillering plants as
irregular-to-oval, longitudinal, reddish-brown
lesions. The lesions often develop pycnidia,
visible as tiny black specks. The center parts of
the lesions tend to become a light brown to white
color. Under conditions conducive to disease
development, lesions often coalesce, causing
entire leaves to die prematurely. Under very
severe conditions, lesions may be found on tips of
glumes. Prolonged, wet-weather conditions,
particularly during the jointing stage with air
temperatures from 15 to 20 ºC, are needed for
severe septoria tritici blotch to occur (Hess and
Shaner 1987; Chungu et al., 2001; Henze et al.,
2007).
SEPTORIA TRITICI BLOTCH
Distribution and losses
Septoria tritici blotch is widespread and an eco-
nomically important disease worldwide (Cook
et al., 1991; Scharen 1999). As is typical of leaf-
spotting pathogens, when infections occur and
become severe on the fl ag leaf or the leaf imme-
diately below it, losses in grain yield and volume
weight will be greatest (Thomas et al., 1989). The
disease decreases the radiation-use effi ciency of
the wheat canopy, and the disease is made more
severe with increasing leaf nitrogen concentration
(Olesen et al., 2003). Although
S. tritici
is able to
Taxonomy and life history
The telomorphic stage of the causal fungus of
septoria tritici blotch is
Mycosphaerella graminic-
ola
(Fuckel) Schroeter, a heterothallic ascomycete
(Sanderson 1972; Kema et al., 1996b; Cunfer and
Ueng 1999). Ascospores are produced in pseudo-
thecia during the growing season on infected
leaves and sometimes on glumes (Garcia and
Marshall 1992). More commonly, pseudothecia
are formed as the crop matures or when infections
