252 
Journal of Agricultural Research 
Vol. I, No. 3 
DIAGNOSIS OF FOOT-ROT 
The foot-rot organism is a slow-growing parasite, especially during 
the earlier stages of infection. During about the first three weeks after 
inoculation, only a slight enlargement of the wound in all directions takes 
place. About three weeks seems to be required for the fungus to over 
come the plant sufficiently to cause any marked reduction in its vitality 
or vigor. As soon, however, as the fungus gets the upper hand, it de¬ 
velops very rapidly and in about one week more completely girdles and 
extends along the stem from 2 to 5 inches, killing the plant by the de¬ 
struction of the cortex. At the end of about another week wilting of 
the leaves is first observed, the plants beginning to die soon afterwards. 
There is considerable variation in the length of time a plant will live 
after becoming infected, especially under greenhouse conditions, some of 
the plants dying in three or four weeks, while others may survive for one 
to four weeks longer. It is also interesting to note in this connection 
that those plants appearing to be the strongest when inoculated are likely 
to be the first to succumb to the disease. An explanation of this may 
be that a vigorously growing plant may stimulate the fungus to more 
rapid development. 
The first sign of the disease of inoculated plants is a blackening of the 
cortex of the stem at the point of inoculation. When inoculated at the 
soil line, the fungus seldom grows more than half an inch below the sur¬ 
face of the ground, but it extends up the stem several inches. The leaves 
near the point of inoculation are invaded and soon turn yellow and fall 
off. Under greenhouse conditions numerous black pycnidia break 
through the epidermis of the stem (PI. XXIII, fig. A) along the black¬ 
ened area about the time the foliage begins to wilt. Under natural con¬ 
ditions in the field, on the other hand, the pycnidia form on the invaded 
tissue before the wilting of the plant. It was observed also that diseased 
plants will survive under field conditions much longer than in pots in 
the greenhouse, where they are naturally handicapped by artificial con¬ 
ditions. Many diseased plants in the field with fruiting bodies abund¬ 
antly formed on the stem are often sustained by the roots which are 
thrown out at the nodes along the stems, although the main stem may 
be nearly destroyed by the fungus. If not supported by roots at the 
nodes, the diseased plants readily succumb. 
As a rule, the disease is confined to the stem of the plant from the soil 
line to 4 or 5 inches above it. However, at Cape Charles, Va., in some 
of the low, rather wet fields, where there was a rank vegetative growth, 
vines were found diseased several feet from the hill. In such cases in¬ 
fection evidently took place at the node and spread in each direction 
(PI. XXIV), the vine on each side of the diseased area remaining healthy. 
The organism isolated from pycnidia on such diseased spots was identical 
with the one obtained from the stem. 
