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A closer look at Gibberella root,
crown and stalk rots
G
ibberella root, crown and stalk rot is caused by the fun-
gal species in the
Gibberella zeae
(
Fusarium graminearum
species complex) with the primary hosts other than maize
being oats, barley, rye, sorghum and wheat.
Of the 16 species belonging to the
Fusarium graminearum
species
complex worldwide, only three are found on maize in South Afri-
ca. These rots are widespread throughout the South African maize
production area, but are particularly common in irrigated maize
fields. Maize grown in monoculture or in rotation with other grami-
naceous host crops can increase disease levels.
Economic importance
Gibberella root, crown and stalk rot is a common problem in
maize production areas worldwide and also in South Africa particu-
larly where wet, warm favourable conditions persist. It can cause
extensive economic losses due to premature plant death and inter-
ference with translocation of water and nutrients during grain fill,
resulting in lodging of plants due to weakened stems (
Photo 1
).
Yield loss depends on a number of factors including genotype,
prevailing climatic conditions, fertilisation rates, crop density and
cultural practices. Although it is difficult to estimate precise yield
loss due to Gibberella root, crown and stalk rot during favourable
environmental conditions, extensive damage (lodging) is known
to occur.
Lodging complicates mechanical operations, necessitating the
picking up of plants and hand harvesting, which increase time, la-
bour and financial constraints.
Symptoms
Symptoms of Gibberella root, crown and stalk rot are similar to
those of other root and stalk rots, but it is the pink/red discoloura-
tion that is diagnostic (
Photo 2
). Affected plants wilt, the leaves
change from light to dull green and the lower stalks become straw
coloured.
Unfortunately, symptoms only become obvious once the damage
has been done. To confirm the disease, it is suggested that produc-
ers remove an infected plant and cut it lengthwise down the stalk to
the root ends.
The tissue should have a red discolouration to it. The internal pith
disintegrates, leaving only the vascular bundles intact. The dis-
integration of stem tissue causes stem lodging and rotting of the
root system which leads to root lodging. Small, round, black fruit-
ing bodies (perithecia) may be produced superficially on the stalks,
often at the internode.
Epidemiology
Under warm, wet conditions, the perithecia produce ascospores
that are disseminated by wind and may infect maize plants. Inoculum
may also be produced as conidia during the summer. Stalk infections
usually occur shortly after pollination, developing at the origin of the
leaf sheaths or around the brace roots. The fungus may also enter
through the roots, crowns and grow up into the lower stem.
Control
Crop rotation
Crop rotation with legume crops or sunflowers will allow stubble to
break down, without providing a host on which to survive, thereby
reducing inoculum. Although recent studies have shown the abil-
ity of a number of the
Fusarium graminearum
complex species to
survive on plant organic matter in or on the soil, it is still important
to rotate with crops that are non-hosts and break down quickly in
the field.
ON FARM LEVEL
Maize / Root rot / Crown rot / Stalk rot
PROF BRADLEY FLETT
and
DR BELINDA JANSE VAN RENSBURG,
ARC-Grain Crops, Potchefstroom
1
Mei 2018
1: Lodging of maize plants caused by Gibberella root, crown and stalk rot.
Integrated pest control