BIOL 4250- Smuts (Exam 2)

Ustilaginomycotina

Subphylum of Basidiomycota; includes smuts and bunts

Common name

“Smut fungi” because teliospores give plants a black, sooty appearance

Teliospore

Thick-walled resting spore where karyogamy occurs

Biotroph

Parasite that obtains nutrients from living plants

Semi-obligate biotrophs

Can sometimes live saprotrophically but mainly parasitic

Haustoria

Specialized feeding structures in some species

Basidiospore + Teliospore stages only

No other spore types

No clamp connections

Unlike many Basidiomycota

Simple septa

Non-clamped cross walls

~1700 species

Infect over 4000 plant species in 75 angiosperm families

Economically important species

corn smut, dwarf bunt, common bunt, Karnal bunt, flag smut

Teliospores

Globose, thick-walled, pigmented; survive long periods (10–25 years)

Sorus (sori)

Mass of teliospores formed in host tissues (ovaries, stems, leaves, roots)

Covered smut

Persistent peridium enclosing spores

Loose smut

Thin peridium that ruptures easily to expose spores

Smuts vs Bunts

Smuts infect vegetative/reproductive tissues; bunts infect ovaries of cereals

Smuts (Ustilaginales)

Infect inflorescences, stems, or leaves

Bunts (Tilletiales)

Infect grains; kernels filled with black spore masses

Common bunt (stinking smut)

Caused by Tilletia tritici and T. laevis; emits fishy odor

Karnal bunt

Caused by Tilletia indica; partially replaces seeds

Corn smut

Ustilago maydis; forms large, black spore-filled galls on corn ears

Life cycle

Yeast-like haploid phase (saprotrophic) and dikaryotic phase (obligate parasite)

Infection sites

Ovaries of grasses, vegetative tissues, or seeds

Spore dissemination

Wind, harvest machinery, or contact

Economic impact

Reduces crop yields and grain quality

Comparison: Rusts vs Smuts

• Rusts: up to 5 spore stages, may need 2 hosts, obligate biotrophs

• Smuts: 2 spore stages, 1 host, semi-obligate biotrophs