Ustilago tritici (Pers.) Rostr.

Synonyms

Erysibe vera β tritici (Pers.) Wallr.
Uredo carbo β tritici (Pers.) DC.
Uredo segetum β tritici Pers.
Uredo segetum β Uredo tritici Pers.
Ustilago ehrenbergiana A.A. Fisch. Waldh.
Ustilago hordei Bref.
Ustilago passerinii A.A. Fisch. Waldh.
Ustilago schumanniana Henn.
Ustilago segetum var. tritici (Pers.) Brunaud
Ustilago segetum var. tritici (Pers.) Rostr. & J.L. Jensen
Ustilago tritici [forma] folicola Henn.
Ustilago ugamica Golovin
Ustilago vavilovii Jaczewski

Description

Sori in spikelets, dark olivaceous brown, dusty (loose smut), usually destroying all floral parts, leaving behind only the naked rachis (in rye usually only parts of the lower spikelets are destroyed); occasionally also as striae on leaves, sheaths and culms.

Spores globose to subglobose or ovoid, 6–9 × 5–7 µm diam., olivaceous brown, paler on one side, minutely echinulate.

Spore germination: Basidia septate, 4-celled. On artificial media and in nature fusion between compatible basidial cells gives rise to dikaryotic hyphae that infect the host via the ovary at flowering, resulting in a systemic disease.

Hosts
   
Host family: Poaceae
   
Host species: Secale cereale L.
Triticum aestivum L.

Distribution

States & Territories: ACT, NSW, QLD, SA, TAS, VIC

Comments

Ustilago tritici occurs worldwide and causes loose smut or flying smut of cultivated wheat. McAlpine (1910: 150) observed almost a century ago that it was common in all Australian States. The loose mass of spores produced by infected plants emerges at about the same time as the healthy wheat flowers. The spores are carried by wind to neighbouring healthy flowers which they infect via the ovary and the embryo of the developing seed. Cool, moist conditions extend the flowering period, giving loose smut spores a greater chance to infect flowers. Loose smut is internally seed-borne and infected seed germinates to produce systemically infected plants in which the ovaries in the spikelets of the developing inflorescence are replaced by smut sori. The smut can be controlled by seed certification, systemic seed treatment fungicides and resistant cultivars.

Ustilago tritici and U. nuda are difficult to distinguish by spore morphology alone, and for this reason several authors have considered them to be conspecific. The differences between the two were summarised by Vánky (1994a: 383).