LOOSE SMUT. OF OATS 
_ There are two smuts of oats, the loose and the covered. Loose smut 
is much the more common and the one usually referred to as oat smut. 
This disease occurs wherever oats are grown and may often destroy from 
25 to 50 percent of the crop. Its control is exceedingly simple and effective. 
SYMPTOMS 
The evidences of loose smut are usually confined to the inflorescence, 
though the leaves may rarely show lesions. Compare the specimens of 
this disease with healthy specimens provided. OBSERVE:— 
1. The striking difference in the panicles of the two; form, size 
and color. DRAW. 
2. In the entire plants (illustration specimens) the relative 
length of straw, number of stalks in the stool, amount and character of 
leafage. . 
3. The differences in the spikelets of each; empty glumes, hull 
and flower parts (most easily determined by dissecting specimens in water). 
Make enlarged DRAWINGS to show comparatively the effects of the dis- 
ease on the parts of the spikelet. 
Compare specimens of loose smut with those of covered smut. SKETCH 
to show differences. 
ETIOLOGY 
The pathogene causing the loose smut of oats is Ustilago Avenae 
(Persoon) Jensen. It is closely related to Ustilago Tritici (Pers.) Jens. 
but differs strikingly in certain features of it slife-history. (See p. 137) 
The covered smut of oats, caused by Ustilago levis (Kell. and Sw.) Mag., 
occurs along with U. Avenae from which it is to be distinguished certainly 
only by its smooth, granular spores. 
Life-history. There are in the life-history of this pathogene only 
primary cycles. While not so intimately associated with the living host 
during the resting-period as is Ustilago Tritict (Pers.) Jens., it normally 
exhibits little saprogenic activity under natural conditions. 
The Primary Cycles are initiated at blossoming-time, at which time 
inoculation occurs. 
Pathogenesis. The smutted plants scattered through the field 
are the sources of inoculum. 
Remove a bit of the black mass from a smutted head to a drop of 
potassium hydroxide on a slide; cover and examine. OBSERVE:— 
4. The numerous brown, globose bodies scattered through 
the mount,—the chlamydospores. 
5. Their color (lighter on one side); markings and variations 
in size. pRaW three different spores. (See demonstration microscope, 
oil-immersion.) 
These chlamvdospores are resting-spores and may retain their vitality 
for several years. 
The chlamydospores, disseminated when the oats are in blossom, 
lodge within the oat hull next to the kernel. They do not germinate 
at once as do those of U. Tritict but lie dormant as the oat hull closes 
about the maturing kernel. The chlamydospores are thus enclosed 
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