Ustilago avenae (Pers.) Rostr.

Synonyms

Erysibe vera γ avenae (Pers.) Wallr.
Erysibe vera δ holci-avenacei Wallr.
Uredo carbo α avenae (Pers.) DC.
Uredo segetum γ avenae Pers.
Uredo segetum γ Uredo avenae Pers.: Pers.
Ustilago aegilopsidis Picbauer
Ustilago arrhenatheri Ferle
Ustilago avenae (Pers.) J.L. Jensen
Ustilago decipiens (Wallr.) Liro
Ustilago haynaldiae Becerescu
Ustilago holci-avenacei (Wallr.) Cif.
Ustilago medians Biedenkopf
Ustilago nigra Tapke
Ustilago perennans Rostr.
Ustilago segetum var. avenae (Pers.) Brunaud
Ustilago segetum var. avenae (Pers.) J.L. Jensen

Description

Sori in spikelets destroying the ovaries, palea, lemma and glumes (loose smut). Infection systemic. Spore mass at first firm, then powdery, dark olivaceous to chocolate-brown.

Spores globose, ovoid to elongate, 6–9 × (4–) 5–7 µm, yellowish brown to olivaceous brown, paler on one side, minutely echinulate; spines usually more prominent on the paler side, in SEM densely spaced rounded to subacute warts.

Spore germination resulting in 4-celled basidia that produce basidiospores on artificial media. Compatible basidial cells or basidiospores fuse to form dikaryotic hyphae that infect seedlings. Under natural conditions (i.e. on seed) basidiospores are rarely formed and do not play a significant role in the initiation of infection. Infective dikaryons arising mostly from fused basidial cells.

Hosts
   
Host family: Poaceae
   
Host species: Arrhenatherum elatius (L.) P.Beauv. ex J.Presl & C.Presl
Avena fatua L.
Avena sativa L.

Distribution

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

Comments

Ustilago avenae causes loose smut of cultivated oats, and it has been known in Australia for more than 100 years (McAlpine, 1910: 147). Seed is externally contaminated by smut spores spread by wind and released during harvesting. When contaminated seed is sown, the spores germinate and infect the seedling before it emerges. The ovaries of these infected plants are replaced by the smut sori. Loose smut of oats can be controlled by the selection of seed from crops known to be free from infection, or by fungicidal seed treatment.

The spores of U. avenae are minutely echinulate, which differentiate it from U. hordei the cause of covered smut of oats and barley. These are the only two smut fungi that are known to occur on oats.