272 
Journal of Agricultural Research 
Vol. XXVI, No. 6 
liana. Lawrence ( 8 ) described a new species of sclerotium-producing 
fungus, which he named Sclerotinia perplexa nov. sp. This fungus attacks 
sunflower, as well as several other plants, causing a disease very similar 
to the one described by Bisby. It differs from Sclerotinia libertiana in 
that it has a conidial stage. A similar disease of sunflower is also de¬ 
scribed by Morris and Swingle (9), who state that the causal fungus 
resembles Sclerotinia libertiana very closely. Jagger ( 6 ) has described 
a new species of Sclerotinia on lettuce, celery, and other crops, similar 
to 5 . libertiana , except that the sclerotia are much smaller. Likewise, 
Dana (4) has reported two new species of Sclerotinia, namely, 5 . gregaria 
and 5 . demissa, which attack Amelanchier cusickii and Prunus demissa 
respectively. These two fungi also have a conidial stage. 
The disease of udo under discussion has been called “rootrot.” The 
stem of the host is also attacked, but less vigorously than the roots. 
The writer has not had an opportunity to observe this disease under field 
conditions, except in the case of a few plants. In these cases the disease 
did not become evident until the plants were about three-fourths grown. 
One large plant, which was observed on October 24, 1920, had 10 to 15 
stems. The leaves were dying from the base of the plant towards the 
top, being at this time dead about two-thirds of the way up. Under the 
conditions to which this plant was subjected the disease seemed to work 
very slowly, requiring practically a whole season to kill the plant 
completely. 
The leaves, as well as the lower part of the stem of the infected plants, 
died and turned brown, and the roots decayed. A number of large, 
black, irregular-shaped sclerotia were usually present on or in the dead 
and dying stems and roots (PI. 1, D). When small plants growing in the 
greenhouse became infected the leaves wilted, the petioles lost their 
turgidity and broke down, and the stems soon became so completely 
decayed that the whole plants collapsed (PI. 2, B and C). In case of small 
plants the petioles which came from beneath the soil rotted (PI. 1, B and 
C), and under humid conditions a mass of white mycelium grew over 
their surfaces. The infected area of the stem was brownish in color and 
had the appearance of being water-soaked or scalded. The small infected 
roots soon became a soft watery mass of more or less isolated cells in¬ 
terwoven with mycelium and later interspersed with sclerotia. 
THE CAUSAE ORGANISM 
Numerous isolations have been made by planting bits of diseased tissue 
from the interior of the root, as well as disinfected sclerotia, on sterile 
culture media. In all cases the same fungus was obtained. After 
growing this fungus on different culture media and using it in making 
numerous inoculations, through a period of two years, the writer is forced 
to conclude, as did Bisby and Morris and Swingle in case of the fungus 
from sunflower, that the fungus which causes the rootrot of udo is very 
similar to, if not identical with, Sclerotinia libertiana. The sclerotia vary 
greatly in size, apparently depending upon the nature of the substratum 
and upon environmental conditions, such as temperature and humidity. 
These, however, do not vary sufficiently to prevent the fungus from being 
classed as 5 . libertiana , since it has been shown by Stevens and Hall ( 11) 
that the sclerotia of this fungus are also variable in size. No conidia other 
than the microconidia have been found, either on the host or in culture. 
The microconidia are similar in size and shape to those of 5 . libertiana. 
