EPWS 310 - PLANT PATHOLOGY
THE SMUTS
Pages 583-593
Today just Smuts
caused by Ustilago spp. and Tilletia spp.
The smuts are in
the order Ustilaginales and are historically very serious.
They are
obligate pathogens: biotrophs. Can be grown in culture but not easily.
They replace
reproductive parts of plants with spores and mycelium and while they do not
often kill the host they can reduce yield to zero.
There are about
six genera of economically important smuts. They are as follows:
Ustilago - smut
of small and coarse grains: Wheat, barley, oats and corn.
Tilletia - covered smut of wheat;
bunt of wheat.
Sphacelotheca - Sorghum smuts.
Urocystis - Onion smut.
Smuts produce
only two types of spores: Teliospores and basidiospores.
They replace
reproductive and sometime vegetative parts of plants with black spore masses
which are either loose or covered to a greater or lesser extent with a
membrane.
Loose and
grain smuts:
Ustilago spp.
These smuts are
no longer very serious but historically were more serious than the rusts
because smut destroys the grain itself.
Corn smut, and
loose smuts of barley, wheat and oats.
These diseases
are not easily discernable until the plant heads and it is too late to treat.
Control can only be preventative.
Corn smut Disease
cycle Figure 11-145
Corn smut can
overseason as teliospores on soil but the other loose smuts overseason as
mycelium in the embryo of living seeds
These fungi grow
with the plant after germination and actually stimulate the plant to grow
better through hormonal action. The smutted heads then release spores to infect
healthy seed heads.
No basidiospores
are produced per se. Instead the teliospores from a basidium which germinates
to form primary mycelium which fuses and then can infect the ovary or embryo of
the seed.
Control?
Loose smut of
wheat life cycle Figure 11-147
Covered Smut
or Bunt:
Tilletia spp.
Also called
stinking smut - This disease is actually two diseases caused by three species
of Tilletia
Common Bunt: Tilletia
caries; T. foetida
Dwarf Bunt: Tilletia
contraversa
Common bunt is
well controlled now in the developing world but Dwarf Bunt is still a problem
in the Pacific Northwest.
Bunt causes
stunting of plants and replaces the endosperm of grain with bunt balls.
Disease cycle : Figure
11-149
Bunt teliospores
germinate to form 8-16 basidiospores (14-30 in T. contraversa).
These are
usually called primary sporidia. These fuse by bridging to form dikaryotic
mycelium which then produces secondary sporidia (dikaryotic) which then germinate
to infect the seedling. Infection can be from the soil or form contaminated
seeds.
Grows
intercellularly and follows growing point of the plant. Grows into kernels and
replaces the endosperm.