nmm sP

THE BRITISH SMUT FUNGI 85
bunt balls, the size, reticulations, colour, and germination of the chlamydospores,
nuclear behaviour, cultural characters, and in their effect on height and^tUlering
of the host (Bressman (1931), Smith (1932 b), Holton (1933), Young (1935),
Mitra (1935), Holton & Heald (1936), Savelescu & Sandu Ville (1939), Spangenberg
& Gutner (1936), Gassner (1938), Hanna (1932), Kienholz & Heald (1930),
Flor (1933), Becker (1936), Melchers (1934), Churchward (1938 a), Rodenhiser &
Holton (1937).
The name dwarf bunt (Young, 1935) has been given to a variety of T. caries
which causes excessive dwarfing and tillering of infected plants and produces
small, relatively hard balls of spores. These have prominent reticulations,
germinate only after prolonged soaking (or at 5° C, see Lowther, 1948), and give
atypical promycelia (see p. 83) (Holton, 1943), Dwarf bunt is largely soilborne
and attacks only autumn-so^vn wheat in the United States (Bamberg,
1941; Holton & Suneson, 1943; Blodgett, 1944). It is suppressed if grown with
T. caries and T. foetida on the same plant (Bamberg et al., 1947).
Tilletia indica Mitra (1931,1935, 1937) is only distinguished from T. caries by
the size of spore—which is said to be nearly double that of T. caries. At first it
was said to be odourless and to cause only partial swelling of the host, but this
was corrected later.
Varietal resistance. The world-wide search for varieties of wheat immune from
bunt (reviewed in Holton & Heald, 1941) brought to Ught certain highly resistant
varieties used in genetical studies by the workers named: Turkey (Gaines, 1920,
1925 a; Gaines & Singleton, 1926); Hohenheimer (Gaines & Smith, 1933); Hussar,
Martin, White Odessa, Banner Berkeley, Turkey, Sherman, Oro (Briggs, 1926-
40; Schlehuber, 1938; Wismer, 1934; Bryan, 1937; Stanford, 1941); Albit
(Bressman & Harris, 1933; Schlehuber, 1933, 1935); Florence (Churchward,
1931, 1932, 1938 b); Garnet (Kildufif, 1933); and Hope (Smith, W. K., 1933;
Clark et al., 1933; Bryan, 1937; Churchward, 1938 b). Certain varieties, such as
Hope, resistant when spring-sown, are susceptible if sown in the autumn (Smith,
W. K., 1932 a, 1933). The main genetical results of crosses between resistant and
susceptible varieties are presented in tabular form by Holton & Heald (1941).
The most clear-cut evidence of segregation involving only one or two main
factors was obtained when the inoculum consisted of a single physiologic race of
bunt (Briggs, 1926-40; Churchward, 1931-58). Three major factors for resistance,
designated M (Martin), H (Hussar), and T (Turkey) with linkage between
T and M were recognized by Briggs (1940). Some varieties of wheat carry
modifying factors (Briggs, 1929, 1930 c). Resistance is dominant, incompletely
dominant, or recessive according to the cross. Although a single factor for
resistance does not govern the reaction to all forms of bunt, one factor may
function for a group of three or more races (Bressman & Harris, 1933; Smith,
W. K., 1933; Gaines & Smith, 1933). The reaction to certain races of the two
species of Tilletia is controlled by the same gene (Gaines & Smith, 1933; Schlehuber,
1935). In a cross between White Odessa and a Turkey X Florence selection,
with two races of bunt in the inoculum, resistance was apparently governed
by six genes (Schlehuber, 1938). A mixture of physiologic races is often used in
practical plant-breeding (Martin, 1936). Holton & Heald (1936) recommend that
the number be limited to ten, since more may dilute the inoculum with a decHne