1. Biotic Diseases (cont.)
Fungal Diseases (cont.)

3. Ergotism

4. Claviceps purpurea on Sea Couch
                                                                                                                                
Claviceps purpurea on Sea Couch

5. 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.

6. It's really not a devastating parasite to the plant
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.

7. Germinating sclerotium
Perithecial head
Stroma
Stalk
Germinating sclerotium

8. L.S. in Perithecial head

9. L.S. in perithecial head showing perithecia containing asci
Causative organism: Claviceps purpurea
perithecium
asci
L.S. in perithecial head showing perithecia containing asci

10. Barley heads infected with covered smut
Ustilago hordei
Barley heads infected with covered smut

11. 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.
Ustilago hordei

12. Causative organism: Ustilago hordei Chlamidospores of Ustilago hordei

13. Loose Smut
Loose smut of wheat caused by Ustilago tritici

14. Barley Loose Smut

15. Loose smut is most obvious just after the plant has headed
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 olive-black 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 wind-blown 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.

16. Digitaria sanguinalis loose smut
Beginning of the sporulation of Ustilago syntherismae on the rachis of Digitaria sanguinalis racemes.
Digitaria sanguinalis loose smut

17. Digitaria sanguinalis loose smut
Spikelets are replaced by a blackish-brown spore mass
Digitaria sanguinalis loose smut

18. Spores of Ustilago syntherismae

19. Scanning electron micrograph of Ustilago syntherismae on Digitaria sanguinalis showing globose echinulate spores

20. Flag smut Wheat plant with severe flag smut infection

21. Dark striping of leaves caused by flag smut

22. 'Cracking' of stem caused by flag smut

23. 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.
Urocystis, flag smut

24. Causal organism: Urocystis agropyri
Sterile cells
Fertile
Chlamidospores
(1 to 4)
Urocystis, flag smut
Chlamidospores forming spore balls

25. Urocystis, flag smut

26. Wheat stem rust

28. Berberis leaf infected with Puccinia graminis

29. 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 C, mild nights 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.

30. 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 disease-free 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.

31. T. S. in infected wheat stem showing uredosorus
with uredospores of Puccinia graminis

32. T. S. in infected wheat stem showing teleutosorus
with teleutospores of Puccinia graminis

33. 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