nmm sP

62
THE BRITISH SMUT FUNGI
progress of invading mycelium, as well as spore development in the mature
plant. He detected seven races of V. avenae and five of U. hordei (as U. kolleri)^
three of which were identical with races isolated fijom field samples 15 years
earher (Sampson, 1925,1929). Two races, GlofU. hordei and L 11 of C/. avenae^
showed identical pathogenicity to a wide range ofl hosts. Race L 16 of U.
avenae was peculiar in producing the symptoms of covered smut upon many
varieties. Oats belonging to the potato and sprig groups oiA. saliva (Marquand,
1922) were susceptible to 11 races of smut, a fact which can be correlated with the
well-known tendency for crops of these old varieties to be heavily smutted (Stapledon,
1921). U. avenae is more common in Britain on oats than U. hordei, only
23 among 120 collections belonged to the smooth-spored species (Radcliffe, 1940).
In all the trials certain varieties stand out as resistant, notably Markton,
Navarro, Victoria, and Black Mesdag, but none is immune from all races
(Coffman et al., 1931; Radelescu, 1935 a; Murphy, Stanton, & CofFman, 1942).
Black Mesdag can be infected by at least four races of U. hordei (Reed & Stanton,
1936; Reed, 1940) and by one or more races of U. avenae (Roemer, Fuchs, &
Isenbeck, 1937; Vaughan, 1938). Markton, at first regarded as immune (Stanton,
Shepherd, & Gaines, 1924), may be slightly infected by some races of
U. hordei (Smith & Bressman, 1931), but it is classed with Navarro and Victoria
as a valuable parent in breeding work, (Stanton, 1933; Murphy, Stanton, &
Coffman, 1942). Fulton, a resistant selection from the cross ]?ulghum XMarkton,
is now known to be susceptible to a new race of U. avenae (Hansing,
Heyne, & Melchers, 1945).
That resistance to smut is usually dominant in oat crosses was shown by
Humphreys & Coffman (1937) from a study of F^ and by others of Fg and Fg
generations. Resistance is governed by one, two, or three pairs of factors
according to the varieties crossed (Barney, 1924; Gaines, 1925; Rosenstiel,
1929; Garber, Giddings, & Hoover, 1929; Schattenberg, 1934; Stanton, Reed,
& Coffman, 1934; Austin & Robertson, 1936; Reed, 1925-40; Reed & Stanton,
1925-37). Resistance to covered^smut is apparently recessive in the cross
Danish Island x Monarch (Reed & Stanton, 1937). Inheritance to the two smuts
is usually independent (Reed, 1931-5; Reed & Stanton, 1937-8), but crosses
involving the resistant variety Black Mesdag show parallel results suggesting
that the same factors, or closely Unked factors, are responsible for resistance to
both smuts (Reed, 1934).
Black Loose Smut of barley, U. avenae (U. nigra, see Fischer, 1943).
This seedling-infecting smut, at first confused with U. nuda, has been known
since 1914 (Johnson, 1914; Tisdale & Tapke, 1924; Tapke, 1932; Ruttle, 1934;
Tapke, 1935 a; Moore & Allison, 1935 b; Leukel, 1936). It has a wide distribution
in the United States (Moore & Allison, 1935 b) and in a recent survey 209 among
500 collections of loose smut of barley belonged to this species (Tapke, 1943).
It is easily distinguished from U. nuda by the abundance of sporidial growth on
2 per cent, potato dextrose agar (Tapke, 1941).
Fischer (1939 a) inoculated a number of grasses with paired monosporidial
cultures of U. nigra and produced infection on Elymus canadensis, Hordeum
Twdosum, and Sitanion jubatum. Tapke (1943 b) records Hordeum 'pusillum as a
host of U. nigra, race 4.