Basidiomycota: Ustilaginomycetes Smut Fungi and Allied Taxa

1. Basidiomycota:UstilaginomycetesSmut Fungi and Allied Taxa

3. Begerow et al. 2006. Mycologia 98: 906-916

4. Subphylum Ustilaginomycotina • 1500 species, 80 genera • Mostly plant pathogenic fungi (biotrophs) • Infect > 4000 species of plants in 75 families of angiosperms • Group united by: • Sequence analysis of large subunit rDNA • Host/parasite zone of interaction • Septal pores lacking parenthesomes, but some with dolipore • Parasitic dikaryotic phase and saprotrophic haploid phase • Many taxa dimorphic, with yeast-like haploid phase and mycelial dikaryotic phase

6. Interaction zones and septal pores in Ustilaginomycetes. From Bauer et al. 2001. The Mycota VII. Part B. Chapter 3.

7. Ustilaginomycetes • Ustilaginales • Urocystales • Exobasidiomycetes • Tilletiales • Malasseziales • Exobasidiales • Georgefischeriales • Entylomatales • Doassansiales • Microstomatales • Entorrhizomycetes • Entorrhizales

8. Smut Fungi • “Smut” comes from the dark masses of teliospores formed by many members of the group

9. Smut Fungi • Economically important pathogens include: • Ustilago maydis (corn smut) • Tilletia controversa (dwarf bunt of wheat) • Tillieta tritici and T. laevis (common bunt) • Tilletia indica (Karnal bunt of wheat) • Urocystis agropyri (flag smut)

10. From Casselton and Olesnicky, 1998

11. Mating Systems in Smut Fungi • Heterothallic/tetrapolar (e.g., Ustilagomaydis) • Two unlinked mating type (MAT) loci a and b • a locus • 2 alleles: a1 and a2 • Includes pheromone and pheromone receptor genes that control cell-to-cell signaling • controls fusion of haploid cells to form dikaryon • b locus • multiple alleles (25 in U. maydis) • regulates filamentous growth of dikaryon • is a main determinant of pathogenicity

12. Mating Systems in Smut Fungi • Heterothallic/bipolar (e.g., Ustilago hordei) • a and b loci are physically linked on one chromosome

13. Basidiospores Basidium Teliospore germination Tilletia-type Ustilago-type

14. Basidial types in Ustilaginomycetes. From Bauer et al. 2001. The Mycota VII. Part B. Chapter 3.

15. Dikaryon formation • Conjugation of primary or secondary basidiospores • Conjugation of basidium cells H-body

16. Secondary Basidiospores (Tilletia) Forcibly discharged, formed from sterigma-like structure Passively dispersed

17. Sorus (pl. sori) • Teliospores are formed in sori • Composed of host and fungal tissues • Formed in host ovaries, stems, leaves, or roots depending on the smut taxon • Characters of taxonomic importance include: • Thread-like structures (fungal) • Sterile cells • Columella (host) • Peridium (host or fungus) • Persistent = covered smut • Thin, breaking down to expose spores = loose smut

19. Teliospores • Formed singly or in spore balls • Mostly globose, pigmented, with thick, ornamented walls • Size ranges from 3.5 to 60 µm diam • Resistant structures, in some species can survive up to 10 years in soil, and 25 years or more under optimal conditions

22. Smut Diseases • Based on location of sorus in host: • Inflorescence smuts • Leaf smuts • Stem smuts • Root smuts

23. Common types of smut diseases • Bunt • Ovary-infecting species of Tilletia that infect cereals • Stinking Bunt • Diseases caused by Tilletia species that produce foetid (fishy) odor

24. Common types of smut diseases • Partial Bunt • Only a portion of seed or inflorescences are bunted, only part of seed is replaced by sorus Tilletia walkeri infecting Loliummultiflorum Karnal bunt (Tilletia indica)

25. Common types of smut diseases • Covered smut • Well-developed, persistent peridium surrounding sorus • Loose smut • Thin, delicate peridium that ruptures easily to expose teliospores

26. Tilletia • Sori usually in reproductive organs of host • Teliospores formed singly, usually pigmented with ornamented walls • Sterile cells present in sorus • Teliospores with foetid odor due to production of trimethylamine • Tilletia-type germination

27. Entyloma • Sori in vegetative organs of host • Teliospores formed singly, permanently embedded in host tissue • Teliospores with pale, smooth walls • Tilletia-type germination

29. Urocystis • Sori mostly in leaves, stems, forming streaks, swellings or galls • Spore balls with pigmented teliospores surrounded by hyaline sterile cells • Tilletia-type germination

31. Ustilago • Sori in reproductive organs or vegetative tissues of host • Teliospores formed singly, usually pigmented with sculptured walls • Sterile cells absent • Ustilago-type germination

33. Thecaphora • Sori in various parts of host, mostly reproductive organs • Spore balls comprising several to many, pigmented, wedge-shaped teliospores with sculptured outer walls • Germination by formation of septate metabasidium, cells form hyphae that fuse to establish dikaryon http://www.redepapa.org/thecaphora.jpg

34. Order Exobasidiales • Plant parasitic fungi • Form holobasidia on leaves, no teliospores formed • Basidiospores become septate during germination • Dimorphic • Four families, two will be covered: • Exobasidiaceae • Graphioloceae

35. Exobasidiaceae: Exobasidium

36. Graphiola