Ustilago nuda (J.L. Jensen)
Kellerm. & Swingle
Ustilago nuda (J.L. Jensen) Rostr.
Ustilago nuda var. foliicola Trotter
Ustilago segetum var. hordei f. nuda J.L. Jensen
Sori in spikelets, dark olivaceous brown, dusty (loose smut), usually destroying all floral parts and leaving behind only the naked rachis; occasionally as striae on leaves, sheaths and culms.
Spores globose to subglobose or ovoid, 6–9 × 5–7 µm, 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 embryo, resulting in a systemic disease.
Hyphae intercellular and intracellular.
||Hordeum vulgare L.
States & Territories: ACT, NSW, NT, QLD, SA, TAS, VIC, WA
Ustilago nuda causes loose smut of cultivated barley. The smut spores are loosely held and spread easily by wind onto the flowers of neighbouring healthy plants. The spores germinate and infect the ovaries, where the smut remains dormant in the embryo. The smut becomes active and causes a systemic infection when infected seeds germinate. Loose smut of barley can be controlled by planting seed from approved sources, fungicidal treatments and the use of resistant cultivars.
Ustilago nuda is morphologically similar to U. tritici (q.v.) which causes loose smut in cultivated wheat. The former has minutely echinulate spores and can be distinguished from U. hordei, the cause of covered smut of barley and oats, which has smooth spores.