Ustilaginomycetes, The Smut fungi
Mycology (Bio 594, Special Topics)
M. Marshall, 2013
Shippensburg University
(See last slide for additional credits)
Agaricomycotina
Mushrooms,
puffballs, shelf fungi,
jelly fungi
Ustilaginomycotina
Smut fungi and allied
taxa
Pucciniomycotina
Rust fungi and allied
taxa
Begerow et al. 2006. Mycologia 98: 906-916
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
Interaction zones and septal pores in Ustilaginomycetes. From Bauer et al. 2001. The
Mycota VII. Part B. Chapter 3.
• Ustilaginomycetes
– Ustilaginales
– Urocystales
• Exobasidiomycetes (we
won’t cover)
–
–
–
–
–
–
–
Tilletiales
Malasseziales
Exobasidiales
Georgefischeriales
Entylomatales
Doassansiales
Microstomatales
• Entorrhizomycetes
– Entorrhizales
The Smut Fungi
• “Smut” term comes
from the dark masses of
teliospores formed by
many members of the
group
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)
From Casselton and Olesnicky, 1998
Mating Systems in Smut Fungi
• Heterothallic/tetrapolar (e.g., Ustilago maydis)
– 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
• Heterothallic/bipolar (e.g., Ustilago hordei)
– a and b loci are physically linked on one chromosome
Teliospore germination
Basidiospores
Basidium
Ustilago-type
Tilletia-type
Basidial types in. From Bauer et al. 2001. The Mycota VII. Part B. Chapter 3.
Ustilaginomycetes
Dikaryon formation
• Conjugation of primary
or secondary
basidiospores
• Conjugation of
basidium cells
H-body
Secondary Basidiospores (Tilletia)
Forcibly discharged, formed from
sterigma-like structure
Passively dispersed
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
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
Teliospores
Smut Diseases
• Based on location of
sorus in host:
–
–
–
–
Inflorescence smuts
Leaf smuts
Stem smuts
Root smuts
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
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
Lolium multiflorum
Karnal bunt (Tilletia indica)
Ustilago
• Sori in reproductive
organs or vegetative
tissues of host
• Teliospores formed
singly, usually
pigmented with
sculptured walls
• Sterile cells absent
• Ustilago-type
germination
Common types of smut diseases
• Covered smut
– Well-developed,
persistent peridium
surrounding sorus
• Loose smut
– Thin, delicate
peridium that
ruptures easily to
expose teliospores
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
Corn Smut, Ustilago maydis
Loose Smut of Wheat, Ustilago nuda, and U. tritici
Covered Smut of wheat, Telletia carries, T. foetida.
Smut “groups”- Overall Chart
This outline is just provided as a convenience for study
purposes - Obtained from Pl. Path. Dept., U. of Nebraska
Smut
groups
sheet A
Smut
Groups
sheet B
Ignore the remainder
Entyloma
• Sori in vegetative
organs of host
• Teliospores formed
singly, permanently
embedded in host
tissue
• Teliospores with pale,
smooth walls
• Tilletia-type
germination
Urocystis
• Sori mostly in leaves,
stems, forming streaks,
swellings or galls
• Spore balls with
pigmented teliospores
surrounded by hyaline
sterile cells
• Tilletia-type
germination
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
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
Exobasidiaceae: Exobasidium
Graphiola
Credits
This presentation has been modified from one posted on
the web by Dr. Lori Carris, Washigton State University
Plant Pathology Dept. from her course: Plant Path 521,
Mycology.