Agriculture Reference
In-Depth Information
diffi culties in managing it within the constraints
imposed by modern cropping systems.
Disease management
Rotation to nonhosts is the primary management
strategy for common root rot. This must be com-
bined with effective management of grassy weeds.
Some benefi t may also be gained by rotation
among cereal hosts, because this acts against
selection for highly aggressive strains (Conner
et al., 1996). Zero-tillage (no-till or direct-drill)
reduces common root rot severity, and shallow
sowing can also reduce contact with inoculum
(Tinline and Spurr 1991). Avoidance of stress in
the crop reduces severity. In general, manage-
ment practices directed at more conspicuous
diseases like take-all and Fusarium crown rot
will also reduce common root rot in most
areas.
A moderate level of resistance is available
among wheat cultivars (Wildermuth et al., 1992).
Most current breeding work is directed against
spot blotch, but there is evidence that at least
some sources of resistance to spot blotch will also
be effective against common root rot (Arabi et al.,
2006).
Symptoms and epidemiology
Symptoms of crown rot are fi rst seen as necrotic
lesions or more general browning on leaf sheaths
and stem tissue. Infections from inoculum in the
soil may appear fi rst as brown lesions on the
subcrown internode (Color Plate 12b) while
those from surface residue occur through the
crown (Color Plate 13b; Summerell et al., 1990).
Infected crown roots exhibit a dry, brown
discoloration.
Infection from rain-splashed conidia may be
through leaf sheaths above the soil surface,
leading to browning fi rst appearing at nodes
above the crown (Jenkinson and Parry 1994). For
all sites of primary infection, the near-uniform
browning may then progress for several inter-
nodes up the stem (Color Plate 13c, left side). A
pink discoloration under leaf sheaths or in other
tissues may also be seen, and orange sporodochia
(conidial masses) can form on nodes under high
humidity. If infected plants are water-stressed
during grain fi lling, premature ripening may
occur, leading to whiteheads (Color Plate 13a).
The whitehead symptom generally does not
occur when moisture is adequate for optimal
plant growth.
Following physiological maturity the fungi
aggressively colonize stem tissue and survive as
mycelium in the infested residues.
Fusarium
culmorum
can also survive as chlamydospores in
the soil.
Fusarium crown rot in most environments
behaves as a monocyclic disease with incidence
being dependent on initial inoculum in the soil or
crop residue (Backhouse 2006). Secondary spread
appears to be limited in dry environments, but
splash dispersal of conidia can be signifi cant in
more humid environments (Jenkinson and Parry
1994). It is not known what role ascospores may
play in infections of stem bases.
High nitrogen levels favor disease in two ways.
The increased leaf area predisposes plants to late-
season water stress under dry conditions, increas-
ing severity (Cook 1980). High nitrogen levels
FUSARIUM CROWN ROT
Fusarium crown rot is a generic term for diseases
of stem bases caused by several species of
Fusar-
ium
. These diseases are also widely known as foot
rot. Crown rot or similar diseases have been
reported from all areas where wheat is grown
(Nelson et al., 1981; Summerell et al., 2001b).
The importance of this disease complex has risen
with increasing adoption of residue retention and
reduced tillage practices, which favor the buildup
of inoculum and greater levels of infection
(Windels and Wiersma 1992; Burgess et al., 1993;
Smiley et al., 1996a).
The fungi which cause Fusarium crown rot can
also incite Fusarium head blight. The focus of
most community concern and research in recent
years has been on head blight because of the
potential for mycotoxin contamination of food
and feedstuffs. However, Fusarium crown rot
remains a serious problem, especially given the
