Ustilago nuda f.sp. hordei (loose: barley smut)

Barley (Hordeum vulgare) is infected during flowering. The developing seed is invaded by fungal hyphae, and when the seed germinates, the hyphae expand into the growing point of the tillers. As the plant grows, the hyphae are passively carried up with the growing point, which results in the development of a smutted ear. This is the first point at which any macroscopic symptoms are visible (Eibel et al., 2005). The ear will contain a mass of olive-brown smut spores, which replace the infected tissue (Jones, 1999; Steffenson et al., 1999).

Loose smut of barley is an historically important disease of barley. Losses are usually minor if the disease is managed by seed treatments and/or seed certification. In the UK, for example, seed certification programmes maintain tolerance levels of U. segetum var. nuda of 0.5% (Maude, 1996). A survey in the UK showed that 25% of farm-saved winter barley seed samples (not subject to certification) had >0.5% infection (Cockerell and Rennie, 1996). Another survey in the UK over the period 1990-93 showed that the infection levels of U. segetum var. nuda in treated and untreated seed lots were 1% and 7%, respectively (Reeves et al., 1994).