nmm sP

THE BRITISH SMUT FUNGI 67
Ustilago maydis (DC.) Corda, Icones Fung., v, p. 3, 1842.
Vstilago mays-zeae Magnus, 1895.
Sori in the inflorescence and other aerial parts of the host as irregular sweUings less
than 1 cm. to more than 10 cm. in length, at first limited by a white or cream membrane
of host and fungus tissue. Spore mass powdery, very dark sepia. Spores
globose or sub-globose to ellipsoidal, epispore bluntly echinulate, 8-12 fi diam.
On Zea mays.
Occasionally recorded in southern England.
Exsiccati: Cooke, Fung. Brit. Exsicc., i, 433; ii, 431.
Spore germination, which has been described by Brefeld (1895) and a number of
other workers, takes place in nutrient solution at any time of the year. Terminal
and lateral uninucleate sporidia are borne on a four-celled promycehum,
singly or in simple or branched chains. Sporidial fusion occurs only under certain
conditions (see p. 42).
Infection of the host. Brefeld (1895) first demonstrated the localized infection of
maize by U. maydis in contrast to the systemic infection of several other cereal
smuts. The fungus can penetrate any part of the plant where the tissue is
meristematic. Walter (1934) described the direct penetration of the epidermal
wall and found that infection might arise either from the promycelium or from
germinating sporidia. Chlamydospores and sporidia are distributed by wind
and are very resistant to low temperature and to desiccation. The smut can ^
multiply and live for some time as a saprophyte in soil (Piemeisel, 1917).
Chlamydospores retained viabihty in pure sand for eight years (Kornfeld, 1937)
and were not always destroyed by silage (Perlet, 1938). In the United States dry
weather conditions are most conducive to infection (Immer & Christensen, 1928).
Racial specialization. Ustilago maydis, a heterothalhc species, comprises an
indefinite number of biotypes differing in pathogenicity and other characters
(Christensen, 1931; Christensen et al., 1929; Hirschhorn & Hirschhom, 1939).
Isolations from a single smut gall differed in their reactions on inbred fines of
maize under artificial methods of inoculation (Eddins, 1929 a), but collections of
smut spores from separate geographical areas were often aHke in pathogenicity
when tested on selfed fines of maize under field conditions. Eesistance and suseeptibUity
are governed by genetic factors. Flint varieties are more susceptible than
dent varieties (Hayes et al., 1924), but rpsistailt selections can be found in most
types of maize, and breeding for resistance offers the most promising method of
control (Immer & Christensen, 1925; Immer, 1927; Immer & Christensen, 1931;
Christensen & Johnson, 1935).
Ustilago striiformis (Westend.) Niessl Stripe Smut of Grasses
Ustilago salvei Berkeley & Broome, 1850.^
' Berkeley & Broome (Notices of British Fungi, No. 482) described V. salvei on Dactylia
glomerata collected by Rev. T. Salwey, St. Martin's, Guernsey. De Toni {Sacc. Syll., va,
p. 485, 1888) listed U. salvei as a synonym of U. striiformis, and Liro (1922) used the name
for a smut on D. glomerata which he considered to be distinct from V. striiformis. Examination
of the Berkeley and Broome type in Herb. Kew. shows the host to be Holcus lanatus
and the fungus to be V. striiformis. As the niles stand at present XJ. salvei Berk. & Br.
appears to be the valid name for the fungus now widely known as V. striiformis, but we agree
with Stevenson (Plant Dis. Beptr, xxx, p. 53,1946) in not advocating the adoption of the
former name.