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Bunt, or stinking
smut |
Causal organism - Tilletia controversa
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The disease cycle of T. controversa matches that of T.
tritici very closely in many respects. Affected plants appear uninfected
until ear emergence. When the ears emerge the seeds are seen to have been
replaced by bunt balls which break open during harvest, contaminating healthy
grain. When contaminated grain is sown the spores on the outside of the grain
germinate, eventually reaching the growing point of the plant. It is at this
stage that T. controversa differs from T. tritici. With common
bunt, the fungus normally infects the plant via the coleoptile
as the seedling is emerging. Rapidly germinating seedlings can develop so
quickly that they can effectively avoid infection. With T. controversa,
there is a long incubation period and a requirement for cool temperatures
before the spores will germinate. Thus, the fungus frequently infects plants
much later in development. The site of penetration of the host plant is presumed
to be the tiller initials.
At harvest, bunt balls contaminate the soil as well as healthy seed but with
dwarf bunt this is very significant as the fungus can survive in soil for
many years. Free spores are reported to remain viable in soil for at least
3 years and bunt balls can survive for up to 10 years.
