Transcript Digitaria sanguinalis loose smut

Biotic Diseases (cont.)
Fungal Diseases (cont.)
Fungal Diseases (cont.)
Ergotism
Smuts
Rusts
Ergotism
Claviceps purpurea on Sea Couch
Syptoms
Claviceps purpurea is commonly found on grains of rye or
sometimes on other grasses such as quackgrass. The fungus
infects the flowers when they're young. It induces the cells to
divide (hyperplasia) and to enlarge (hypertrophy), creating the
relatively large brown sclerotia. These sclerotia are hard resting
structures that allow the fungus to survive adverse conditions,
such as winter and desiccation.
In the life cycle of this organism, the sclerotia fall to the
ground and overwinter, germinating in the spring to produce a
stroma that contains perithecia, which produces spores.
It's really not a devastating parasite to the plant. You might think
its main detriment is that it replaces one of the grains of the plant,
thus reducing yield. However it also draws nutrients away from the
other uninfected grains so that they become stunted, thus reducing
yield quite a bit more. But its worst problem is when the sclerotia
inadvertently get mixed in with the grains and are incorporated into
foods, thus causing a devastating and sometimes deadly syndrome
called ergotism in humans and other animals.
Ergotism is caused by the chemicals in the fungus called ergot.
Consumption of foods contaminated with ergot and ergot
derivatives may cause vomiting, diarrhea, hallucinations, and may
lead to gangrene in serious cases.
Perithecial head
Stroma
Stalk
Germinating sclerotium
L.S. in Perithecial head
Causative organism: Claviceps purpurea
perithecium
asci
L.S. in perithecial head showing perithecia containing asci
Covered Smut
Barley heads infected with covered smut
Symptoms:
Losses from the Covered smut disease are rare because the
environments are not conducive. In addition, seed treatments have
reduced incidence of the disease. However, because heads
infected with covered smut are harvested with healthy grain,
losses can arise from lowered grade due to smutty grain.
Causative organism: Ustilago hordei
Chlamidospores of Ustilago hordei
Loose Smut
Loose smut of wheat caused by Ustilago tritici
Barley Loose Smut
Loose smut is most obvious just after the plant has headed.
Diseased plants produce blackened heads among a field of green
heads. The spikelets of colonized heads become a mass of oliveblack spores that have a characteristic "dead fish" odor. The fungus
that causes loose smut survives as dormant mycelia (fungal
threads) within the embryo of an infested seed. When the seed
germinates, the fungus resumes growth along with the shoot apex.
As the juvenile head develops within the stem the fungus colonizes
the seed primordia (tissue that would become a seed within a head).
When the head emerges from the boot, instead of flowering and
releasing pollen, it releases the olive-black spores that can be windblown to "healthy" flowering heads. The spore germinates on the
stigma (female receptive portion of flower) of a healthy head and
colonizes the developing seed embryo. The colonized seed appears
healthy but carries the dormant smut fungus within to start the
cycle over again with the planting of the seed.
Beginning of the sporulation of Ustilago syntherismae on the rachis of Digitaria
sanguinalis racemes.
Digitaria sanguinalis loose smut
Spikelets are replaced by a blackish-brown spore mass
Digitaria sanguinalis loose smut
Spores of Ustilago syntherismae
Scanning electron micrograph of Ustilago syntherismae
on Digitaria sanguinalis showing globose echinulate spores
Flag smut
Wheat plant with severe flag smut infection
Dark striping of leaves caused by flag smut
'Cracking' of stem caused by flag smut
Symptoms
Affected plants are severely stunted. The ears fail to emerge,
remaining within the boot. Plants show long dark grey to black
streaks on the leaf blades and leaf sheaths. The streaks eventually
erupt, giving the leaves a ragged appearance and exposing the
black teliospores which are then dispersed, giving the plants the
appearance of being covered in soot.
Causal organism: Urocystis agropyri
Sterile cells
Fertile
Chlamidospores
(1 to 4)
Chlamidospores forming spore balls
Wheat stem rust
Berberis leaf infected with Puccinia graminis
SYMPTOMS:
Uredinia generally appear as oval lesions on leaf sheaths, true
stem, and spike. Uredinia can appear on the leaves if other diseases
have not killed them. Uredinia are brick red in color and can be
seen to rupture the host epidermis, on the leaves uredinia generally
penetrate to sporulate on both surfaces. Infected areas are rough to
the touch.
Stem rust is favored by hot days 25-30 C, mild nights 15-20 C
with adequate moisture for night time dews. Wind can effectively
disperse urediniospores over great distances. Rain is necessary for
effective deposition of uredinospore involved in regional spore
transport.
Disease dispersal through aeciospores from Berberis vulgaris is
currently rare, but historically it was an important source of
inoculum. Mycelium or uredinia on volunteer wheat, are the most
important source of inoculum in tropical and subtropical climates.
Urediniospores and aeciospore germinate when in contact with
free water. Infection is by penetration through the stoma.
Penetration requires at least a low light intensity.
Stem rust can survive as teliospores during winter when
aeciospores are a major source of inoculum. It generally survives as
mycelium or uredinia on volunteer wheat during the non-wheat
growing season. Uredinospore can be spread by wind into diseasefree areas. Sporulating uredinia are active in tropical and some
subtropical areas throughout the winter. Occasional dormant
mycelium may survive beneath the snow pack in more northern
temperate regions.
Urediniospores and aeciospores are wind borne. Teliospores
remain with the straw.
T. S. in infected wheat stem showing uredosorus
with uredospores of Puccinia graminis
T. S. in infected wheat stem showing teleutosorus
with teleutospores of Puccinia graminis
T.S. in infected Berberis leaf showing
pycnidium with pycniospores of
Puccinia graminis
T.S. in infected Berberis leaf
showing aecidial cup with
aeciospores of Puccinia graminis