Mar. 12,1917 
Fusarium-Blight of the Soybean 
425 
word describing the most prominent symptom on the foliage and the 
latter retaining the idea of its relationship to other wilt diseases pro¬ 
duced by species of Fusarium. 
Soybean blight or wilt may make its appearance on individual plants, 
but does not cause the death of all the plants within definite areas, as 
in the case of cotton wilt. 
Although no definite effort has been made to determine the method 
of entrance of the organism into the host, it is thought that it enters 
through the smaller roots in practically the same manner as that 
described for other diseases of this character. Many of the fibrous 
roots are destroyed, and new roots are formed of insufficient number, 
however, to maintain the life of the plant. 
Perhaps the most prominent symptom is a browning or blackening 
of -the interior of the stems and roots. As soon as the leaflets begin to 
drop, this discoloration is evident when the root and stem are split 
longitudinally. This character is shown in Plate 95, figures B and C, 
showing healthy and diseased stems, respectively. As the disease pro¬ 
gresses, the discoloration extends - upward in the stem for one-half or 
more of its length. The tracheal tubes of affected stems when cut 
obliquely show as brown spots. The relative amount of discoloration in 
general and the depth of color in affected xylem portions is less in soy¬ 
beans than in cowpeas. 
A large number of stained free-hand sections were made of stems at 
all stages of development of the disease. In the early stage, only the 
xylem tubes nearest the pith were found to contain the fungus filaments. 
The pith had disappeared in both normal and diseased plants of mod¬ 
erate size. Later, other of these tubes throughout the xylem area are 
penetrated and become filled to a large extent with a network of fungus 
filaments. In still more advanced stages, all of the xylem elements 
(fig. x, A-G ) were found to contain the fungus; and, in addition, the 
cortical parenchyma was invaded. 
The surface of stems of plants in advanced stages of the disease 
generally have salmon-colored spore masses, sporodochia, thickly and 
irregularly distributed Over them. 1 This character is shown by the 
roughened appearance of the stem in Plate 95 > A. The spore masses 
are composed of macroconidia of the fungus and are frequently found 
to occur on plants whose upper leaves are still healthy in appearance. 
Sometimes they are formed only in more advanced stages of the disease. 
MANNER OF INFECTION AND SPREAD OF THE DISEASE 
As stated above, the fungus may enter the plant through the small 
roots. In addition to the spread of the organism through the soil, 
spores are so abundantly produced that drainage water, implements, 
1 Sporodochia on stems of cowpeas are reported by Orton (16, p. 9) to appear after the death of the 
plants. 
