j Fusarium Blight of the Soy Bean 13 
I Instead of applying the name “wilt,” therefore, to the soy 
I bean trouble, it is thought desirable to call it “blight.” This 
I word describes the most prominent symptom on the foliage, 
j That plants are often almost indifferent, for some time, to the 
! fungus which may even be abundantly present within it, is shown 
I not onl}^ by the absence of wilt but also by the fact that many of 
' the plants mature a reduced crop of beans in spite of the disease. 
Affected plants in such cases are stunted and mature earlier than 
; healthy j)lants. In contrast to this, 100 per cent of the cow^peas 
in rows in different parts of the same field are infected, most of 
them die before reaching a height of 2 dm., and the scattered 
plants then remaining may all die before blooming. 
Perhaps the most prominent symptom is a browning of the 
interior of the stems and roots. By the time the lower leaflets 
or leaves begin to dro23, this discoloration is evident well up into 
the stem and, if necessary, by removing the petioles, infected 
plants may be noted from the brown color of the bundle scars 
when no other positive symptom is to be observed. As the dis- 
i ease progresses, the discoloration extends in some cases to the tip 
of the stem and into the bundles of the leaflets. The tracheal 
' tubes of affected stems when cut obliquely show as brown specks, 
i The relative amount of discoloration in general and the depth 
I of color in affected xylem portions is less in soy beans than in 
cowpeas. Healthy and diseased stems are shoAvn in Figure 2, B 
and C. respectiA^ely. 
The surface of stems of j^lants in adA^anced stages of the dis- 
ease in the field generally liaA^e salmon-colored spore masses, 
sporodochia, thickH and irregnlarly distributed OA^er them.i This 
character is shoAvn by the roughened appearance of the stem in 
Figure 2, A. The spore masses are composed of macroconidia of 
the fungus and are frequently found to occur on plants, the upper 
leaA'^es of which are still healthy in appearance. Sometimes they 
are formed onH in more adA^^anced stages of the disease. 
ETIOLOGY 
, Sterile seedlings had been groAvn in test tubes by the method 
I described later in this paper for use as a culture medium to main- 
tain the Aurulence of the organism. In 1915 the roots of such 
seedlings, inoculated after the deA^elopment of the first true leaA^es, 
Avere found in a few days to be penetrated by the fungus thru 
stomata and eiDidermis. The roots were mounted directly on slides 
in a glycerin-eosin water solution and examined under the micro- 
^Sporodochia on stems of cowpeas are reported by Orton (19, p. 9) to appear after 
the death of the plants. 
