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spread of the disease throughout some production areas in recent
years.
On sorghum, symptoms only become evident at flowering. Smut
sori replace all or part of the panicle. Initially sori are covered with a
white membrane which ruptures to release a mass of black spores.
Within the sorus distinct strands of host tissues are preserved which
become visible as spores are released.
Other less obvious symptoms of infection by
S. reiliana
are
dwarfing by some cultivars, excess tillering and a weakened root
system. Often smutted plants show greater root and stalk rot than
unsmutted plants. In some instances, smutted heads only appear on
tillers while the primary head remains sterile and produces no grain.
Soilborne spores of
S. reiliana
germinate and penetrate seedling tis-
sues. After infection the fungus continues to grow systemically and
colonises the tissues of the apical meristem. Invaded floral tissues
are transformed into the black spore mass at flowering and it is only
at this stage that infection is evident. Released spores are re-incor-
porated into the soil for the next cycle of infection.
Spores can survive for a number of years in a dormant state. Condi-
tions for infection have not been extensively studied. However, slow-
er seedling growth induced by low soil temperatures (<12°C) can
promote colonisation of the apical meristem by the pathogen. Thus,
as with seedling blights, delaying of planting until soils have had
time to warm up and ensure rapid seedling emergence can reduce
the risk of infection. Excessive planting depths may also favour
head smut.
1: Charcoal rot of sorghum characterised by black micro-sclerotia within the stalk tissues.
2: Seedling blight and damping off of sorghum.
3: Head smut of sorghum.
4: Ergot of sorghum characterised by a sticky exudate that exudes from infected florets.
5: Grain mould of sorghum.
6: Leaf blight of sorghum with the typical oval leaf lesion and distinct red to tan border.
7: Anthracnose of sorghum where coalescing lesions may cause extensive leaf area loss.
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