Sept. 1, 1924 
Stripe Rust 
215 
ON WHEAT 
On the leaves of adult wheat plants, 
the uredinia develop in end-to-end 
series between the vascular bundles, 
forming long stripes, sometimes ex¬ 
tending throughout the length of the 
leaf. Many of these, developing side 
by side, seem to coalesce, thus com¬ 
pletely transforming one or the other, 
or both, surfaces of the leaf to a mass 
of uredinia. Most commonly the rust 
-occurs on the leaf blades, but it appears 
not infrequently also on the leaf sheaths, 
and in certain peculiarly susceptible 
varieties of wheat the glumes, awns, 
and kernels are severely attacked. On 
the leaf blades of adult plants, the 
uredinia are irregularly scattered and 
strikingly characteristic as to form and 
color. In general appearance they are 
much the same on both sides of the 
leaf. They are narrowly oblong to 
linear in form, sharply delimited later¬ 
ally and less so at the ends (PI. 1, a and 
b). Individually, they vary in extent 
from about 1 to 3 mm. in width and 
from 10 to 110 mm. in length. When 
urediniospores alone are present, the 
color of the stripelike lesions is a red¬ 
dish orange yellow when the uredinia 
are open and lemon yellow when they 
are not open. Mikado orange to capu- 
cine yellow, according to Ridgway (21). 
On the more susceptible varieties, 
where uredinia are numerous on the 
same leaf blade, the attacked areas not 
uncommonly coalesce, either laterally, 
or end-to-end, or both, to such an 
extent that practically the entire leaf 
blade, or large portions of it, may be 
involved. On the sheaths, similar 
stripelike lesions occur, but they 
usually are fewer and less conspicuous. 
On the glumes, the attack is strikingly 
characteristic, especially on certain 
varieties of wheat wdiicRare apparently 
more susceptible than others in these 
organs. 
When the wheat heads are normally 
green, those attacked by the rust take 
on varying shades of yellowish green 
because of deficient chlorophyll in 
affected glumes. The number and 
distribution of glumes attacked on 
individual wheat heads may vary 
considerably, from a single glume to 
several widely scattered. In those 
heads where infection is most general 
and pronounced, all the glumes may 
be rusted. The uredinia and telia 
develop almost entirely on the ventral 
side of the glume, thus causing the 
color and general appearance of rusted 
heads to vary according to the severity 
of the infection. In milder cases only 
slight discoloration is noticeable. In¬ 
stances of severe infection are charac¬ 
terized by marked discoloration and an 
abundance of free urediniospores which 
accumulate in such numbers as to form 
a yellow’ powdery mass on the in¬ 
ner surface of the glumes and over 
the developing kernel (PI. 1, d ). Like¬ 
wise, the kernels vary markedly in 
appearance, depending on the severity 
of attack. When there are but few’ 
uredipia on the glumes, there usually 
is little or no shrinkage of the kernels; 
but w’hen the infection develops early 
and becomes severe, the damage is 
fully as marked as that resulting from 
a like infection of stem rust (PI. 1, c). 
When such kernels are sectioned and 
examined with the microscope they 
usually are found infected to a greater 
or less extent. In such infected ker¬ 
nels, the spores are produced in charac¬ 
teristic pockets in the pericarp as shown 
in Figure 2, and also by Eriksson and 
Henning (4, PL 9). 
In seedling infection, the uredinia 
appear in more or less rounded patches 
without any seeming tendency to form 
stripes. Indeed, in this stage of its 
development stripe rust does not 
differ markedly from orange leaf rust 
(Puccinia triticina Erikss.), except that 
in the latter the distribution of the 
uredinia is more general over the sur¬ 
face of the leaf, and the color of the 
spores in mass is darker yellow, more 
typically orange in color. This notice¬ 
able difference between the disposition 
and character of the uredinia on the 
leaves of adult and seedling plants is to 
be explained on purely anatomical 
grounds, as has been pointed out by 
Eriksson and Henning (4 ). Struc¬ 
turally, the seedling leaf is sparingly 
supplied wdth vascular tissue and is 
markedly succulent (fig. 3, A). The 
relative absence of vascular tissue con¬ 
tributes to the easy and general spread 
of the mycelium and -the irregular 
eruption of the surface as outlets for the 
urediniospores. In the older or adult 
leaves, the vascular bundles check the 
spread of rust laterally and confine it 
to rather sharply defined areas, usually 
