nmm sP

TECHNIQUE 45
barley with loose smut at HaUe, Germany, and elsewhere (Tiemann, 1925;
Seiffert, 1926; Piekenbrock, 1927 ; Grevel, 1930; Zeiner, 1932; Nahmmaoher,
1932; Radelescu, 1935 b; Roemer, Fuchs, & Isenbeck, 1937). One drawback to
its use is the danger of introducing between the pales excessive numbers of spores
which lead to a high death-rate among plants grown from inoculated seed. To
obviate this, the inoculum is diluted with 95-9 per cent, of dead spores, kiUed
with ether or by exposure to dry heat at 150° C. for several hours (Thren, 1938).
(c) Partial vacuum method applied to cereals in flower. A suspension of spores
of Ustilago nuda is made by shaking two medium-sized smutted heads in 100 ml.
of water in a conical flask. An apparatus was designed by Moore (1936) for
bringing the suspension into direct contact with ears of growing wheat or barley.
A partial vacuum is created by the aid of a large automobUe pump with an
inverted plunger-leather, and air withdrawn from the florets is replaced by the
suspension of spores. Oort (1939, 1940) found that, with slight modifications,
four heads could be treated at one time. Vanderwalle (1945), using a rotary
vacuum pump, inoculated 180 ears per hour and obtained up to 98 per cent, of
smut in many lines of barley which showed only slight smut in ordinary culture.
Atkins (1943) found that four heads gave ample seed for testing the resistance
of a variety to loose smut.
The optimum period for inoculation is at mid-anthesis and lasts for a few days
only. The most efiective concentrations of spores in the suspension are 1 gm.
for wheat smut and 0-1 gm. per litre for barley smut. The winter hardiness of
plants raised from seed inoculated by this method is only 10 to 20 per cent,
below normal. Heads of uniform maturity should be selected for inoculation,
but even so results are sometimes inconsistent (Middleton & Chapman, 1941).
{d) Use of a hypodermic needle. A suspension of chlamydospores in 1 per cent,
glucose solution held in a rubber bulb of 10 ml. capacity is injected by means of
a 1-in. 25-gauge hypodermic needle into each floret of a spike of barley a day or
two after the exsertion of the inflorescence. Thirty to forty heads can be inoculated
in one hour (Poehlman, 1945, 1947). See also Bever, 1947.
Shoot infection. The hypodermic injection of maize and other cereals. Monosporidial
lines of U. maydis are grown separately in a solution of 2 per cent,
dextrose and 1 per cent, malt syrup and allowed to develop for two to three
weeks before inoculations are made. They are then strained through cheesecloth
to remove the largest clumps of sohdjuaterial. Cultures for test are mixed
just before inoculation and the inoculum is injected into plants by means of a
hypodermic syringe as near to the growing-point as possible. Controls are
inoculated in the same manner with sterile nutrient solution (Tisdale & Johnston,
1926; Stakman & Christensen, 1927 ; Stakman et al, 1929; Hanna, 1929; Platz,
1929).
Maize plants inoculated wben one week old produce gaUs in three to four
weeks at a glasshouse temperature of 27°-32° C. and it is possible to grow ten
generations of chlamydospores of U. maydis within a year (Schmitt, 1940).
Artificial inoculation will cause infection in some lines of maize resistant to smut
in the field (Grifliths, 1928; Griffiths & Humphrey, 1929; Platz, 1929).
Higher infection results if the sporidia are suspended in a fluid having a
low surface tension. Bavis (1935) obtained good results with a 1 per cent, fish
oil-soap-carrot decoction having a surface tension of 34-0 dynes per sq. cm.