Hosts and Symptoms
The major symptom of loose smut is the "smutted" grain heads, which contain masses of black or brown spores where the grain would normally be. The spores completely replace the grain head so that there is no grain to be harvested on infected plants. It may be possible to identify infected plants in the field before they reach the flowering stage by looking for plants which are taller and more mature than the rest of the field. The fungus causes infected plants to grow slightly taller and mature slightly sooner than the uninfected plants in the field. Since it must infect through the open florets, this gives the fungus a competitive advantage by allowing it to fall down to the healthy plants and insuring that the fungus has a little extra time to produce and disperse spores before the florets of the healthy plants open.
Ustilago nuda infects barley (Hordeum vulgare L.) but there are many strains of Ustilago which infect many different cereal crops in a similar manner. Ustilago tritici, for example, is loose smut of wheat. Unlike some Basidiomycete fungal pathogens, Ustilago spp. infect only one host plant, and do not need to move to an alternate host to complete their disease cycle.
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