Agriculture Reference
In-Depth Information
also increase incidence of infection (Smiley et al.,
1996a), presumably by increasing susceptibility.
Zinc defi ciency may also increase susceptibility
(Grewal et al., 1996).
2006), occurs at low frequency in the Mediterra-
nean region and Asia (Bentley et al., 2006; Tunalı
et al., 2008), and has not been reported from
South America or Europe north of the Alps.
The role of
F
.
graminearum
as a cause of
Fusarium crown rot is unclear because of uncer-
tainty about the identity of fungi reported under
this name. In literature prior to the 1980s
F
.
pseu-
dograminearum
was reported as
F
.
graminearum
,
and even recently the two species have not always
been distinguished. O'Donnell et al. (2004) seg-
regated
F. graminearum
from eight cryptic sister
species, many of which also occurred on cereals.
Fusarium
graminearum
in the strict sense is best
known as a head blight pathogen. It is frequently
isolated from wheat stem tissue and shows a
similar range of aggressiveness to wheat crowns
as
F
.
pseudograminearum
in pathogenicity tests
under controlled conditions (Akinsanmi et al.,
2004). However, surveys in several countries
which have used modern taxonomic concepts
have generally failed to report
F
.
graminearum
as
a signifi cant component of the Fusarium crown
rot complex compared with other species (Pettitt
et al., 2003; Akinsanmi et al., 2004; Backhouse
et al., 2004; Smiley et al., 2005b). The teleo-
morph,
G. zeae
, occurs readily in the fi eld, unlike
other species in the complex.
Fusarium avenaceum
is typically prevalent in
cooler climates such as eastern Canada and north-
ern Europe (Hall and Sutton 1998; Pettitt et al.,
2003), although it occurs more widely as a minor
component of the disease complex. Pathogenicity
to wheat subcrown internodes and crowns is
similar to that of
F. culmorum, F. graminearum
,
and
F. pseudograminearum
(Fernandez and Chen
2005; Smiley et al., 2005b). The teleomorph,
G.
avenacea
, has not been found in the fi eld.
Fusar-
ium
avenaceum
appears to have a broader host
range than the other species but is more frequently
associated with diseases of legumes (Satyaprasad
et al., 2000).
Causal organisms
A large number of
Fusarium
species are capable
of causing stem base disease in wheat (Akinsanmi
et al., 2004). Of these,
F
.
culmorum
(W. G. Smith)
Sacc.,
F
.
pseudograminearum
O'Donnell & T.
Aoki (teleomorph =
Gibberella coronicola
T. Aoki
& O'Donnell),
F
.
graminearum
Schwabe [teleo-
morph =
G. zeae
(Schwein.) Petch], and
F
.
avena-
ceum
(Fr.) Sacc. (teleomorph =
G. avenacea
R.J.
Cook) have been considered the most important
species worldwide.
Fusarium culmorum
has the most widespread
recorded distribution from wheat stem bases
among these species, being found on all conti-
nents. Parry et al. (1994) suggested that
F. culmo-
rum
was typically found in warmer, drier cereal
growing areas. However, surveys in Australia and
North America indicate that it is most prevalent
in the cooler or higher rainfall parts of the wheat
growing areas in these regions (Smiley and
Patterson 1996; Backhouse et al., 2004).
Fusarium
culmorum
differs from the other species in that
chlamydospores play an important part in
epidemiology (Sitton and Cook 1981). Infection
rates are less affected by surface plant residues
compared with other species associated with
crown rot (Windels and Wiersma 1992). No teleo-
morph is known, but evidence for recombination
has been found in fi eld populations (Tóth et al.,
2004), and it is likely that a sexual state does
exist.
Fusarium pseudograminearum
was formerly
known as
F
.
graminearum
Group 1 (Aoki and
O'Donnell 1999). The teleomorph,
G. coronicola
,
is rarely found in the fi eld (Summerell et al.,
2001a). This species is the most important cause
of crown rot in Australia and South Africa
(Burgess et al., 1975; Van Wyk et al., 1987;
Backhouse and Burgess 2002; Chakraborty et al.,
2006). It is also prevalent in western North
America (Smiley and Patterson 1996; Clear et al.,
Disease management
Chemical control of Fusarium crown rot is gener-
ally unsuccessful. Management therefore depends
