LOOSE SMUT OF WHEAT 
This disease is exceedingly common and often destructive in the wheat- 
fields of eastern United States and Canada. It is readily distinguished 
from the stinking smut. The latter, while not uncommon in the east, 
is much more general and destructive than loose smut in the great wheat- 
lands of the west. While the loose smuts of wheat and oats are much alike 
in general appearance, they differ strikingly in certain features of the life- 
history of the respective pathogenes. 
SYMPTOMS 
The evidences of the disease are to be observed chiefly in the heads at 
blossoming-time. Compare the diseased and healthy heads provided. 
NOTE -— 
1. The general effect of the disease on the form and appearance 
of the head. Does it affect the rachis as to length and size; length of 
internodes? pRaw both diseased and healthy heads. 
2. The effect on the individual spikelets. Determine this by 
carefully dissecting out the parts of the (moistened) healthy spikelets 
and flowers. praw. Dissect and praw the parts of the diseased spikelet. 
3. That the culms of a diseased plant at first grow more rapidly 
and outstrip those of the healthy plant. Eventually,.after spore dispersal, 
the healthy culms push up above the diseased ones. (See whether later 
‘studies will explain this.) 
4. The naked rachides from which the spore-masses have 
disappeared. DRAW. 
ETIOLOGY 
The loose smut of wheat is caused by the basidiomycetous parasite, 
Ustilago Tritici (Persoon) Jensen. It is a member of the order of primitive 
basidiomycetes, the Ustilaginales commonly known as the smut-fungi. 
‘There are two families in this order, the Ustilaginaceae to which U. Tritict 
belongs and the Tilletiaceae to which belongs the stinking smut-pathogenes, 
Tilletia Tritict (Bjerk.) Wint. and Tulletia foetens (B. and C.) Trel. 
Life-history. While the parasite causing this disease has long been 
known, it is but recently that its life-history has been completely under- 
stood. (See Pl. Ind. Bur. Bul. 152:10-12.) It differs, along with U. nuda 
(Jens.) Kell. and Sw. in barley, from most of the other smut-fungi whose 
life-history is known, in that infection occurs through the stigmatic sur- 
faces of the pistil at flowering-time. There are no secondary cycles. 
The Primary Cycle requires a full year for its completion. There is 
no saprogenesis, the pathogene remaining in continuous association with 
the living host except for the few minutes during transfer from the source 
of inoculum to the infection-court. 
Pathogenesis. The black smutted heads emerging from the upper 
leaf-sheaths at flowering-time constitute the sources of inoculum. 
Mount some of the sooty mass in a drop of potassium hydroxide, cover 
and examine with the high-power. OBSERVE :— 
5. The numerous brown globose bodies scattered through the 
mount,—the chlamydospores. These, in the case of this smut-fungus, 
constitute the inoculum. 
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