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58 THE BRITISH SMUT FUNGI<br />

Ustilago hordei (Pers.) Lagerh. Covered Smut of Barley and Oats<br />

[Beticularia segetum BuUiard, 1791, P-p.]<br />

Uredo segetum subsp. hordei Persoon, Synopsis, p. 224, 1801.<br />

Uredo carbo de Candolle, 1815 [nov. nom. for U. segetum] p.p.<br />

Ustilago segetum (Pers.) Ditmar, 1817 [as ' U. segetum Link'] p.p.<br />

Ustilago carbo (DC.) Tulasne, 1847, p.p.<br />

Ustilago hordei (Pers.) Lagerheim, Mitt, badischen bat. Ver., p. 70 (March) 1889.'<br />

Ustilago avenae var. levis KeUerman & Swingle, 1890.<br />

Ustilago kolleri WiUe, 1893.<br />

Ustilago levis (Kellerm. & Swing.) Magnus, 1894.<br />

Sori in the spikelets replacing the ovaries and more or less of the tissues within<br />

the glumes. Spore mass firm, brown- or purpUsh-black, partly (or rarely completely)<br />

hidden by the glumes. Spores spherical to subspherical, pale yellow or<br />

greenish-brown, lighter in colour on one side than the other, smooth, 7-11<br />

(av. 8-5-9-0) fj, diam.<br />

On barley (Hordeum) and oats (Avena) causing Covered Smut.<br />

July-Sept. Widespread. Common.<br />

Spore germination has been studied by Fischer von Waldheim (1869), Kellerman<br />

& Swingle (1890), Brefeld (1895), Herzberg (1895), McAlpine (1910), Paravicini<br />

(1917), and others (see Liro, 1924). Stakman (1913), using a-race from barley,<br />

found that some spores germinated on water in 6^ hours and nearly all in<br />

24 hours. The growth of promycelia and sporidia follows the same plan as<br />

U. avenae (see p. 61).<br />

Infection of the host occurs during germination from spores lying on the surface of<br />

the grain or between the pales and the caryopsis. See p. 43.<br />

Racial specialization. Jacqzewski (1925) reported on the natural occurrence of<br />

U. hordei on rye in Siberia, and in the United States it occurs on Agropyron<br />

cristatum and Elymus glaucus jepsoni. Fischer (1939 a), using paired monosporidial<br />

cultures of covered smut from these hosts, produced infection on<br />

two varieties of barley and on the following grasses: Agropyron caninum, E.<br />

canadensis, E. glaucus jepsoni, E. sibiricus, Hordeum nodosum, and Sitanion<br />

jubatum. This race was physiologically distinct from covered smut of oats.<br />

Faris (1924 b) gives a table showing the infection of four differential varieties<br />

of barley by five physiologic races. Rodenhiser (1928), dealing mainly with<br />

cultural races, found that two differed also in pathogenicity. Aamodt & Johnston<br />

(1935) reported on two physiologic races at Alberta. Semeniuk (1940) in the<br />

same State detected four physiologic races in 1935-7 with an unexplained change<br />

in pathogenicity in 1938. Allison (1937) found that 27 out of 28 collections of<br />

covered smut could be differentiated on six varieties of barley, the type of<br />

infection varying with the race. Tapke (1937 b) distinguished eight races (including<br />

those of Faris) on five varieties of spring barley. Odessa was susceptible to<br />

all races. Later, 13 races were differentiated on eight varieties (Tapke, 1945,<br />

Table 1). New races were obtained by screening certain collections. Apart<br />

from pathogenicity, races differed in the size of colour of the chlamydospores,<br />

relative smoothness of the walls, degree of compactness of the heads, and mode

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