620 
Journal of Agricultural Research 
Vol. XXXI, No. 7 
tinia found parasitizing sunflowers in Manitoba and obtained positive 
results. The results obtained in the present experiments, neverthe¬ 
less, indicate that the potato tuber is highly resistant to infection by 
Sclerotinia. This is in entire agreement with experiences in the 
market. Up to the present time not a single tuber has been found 
affected with Sclerotinia rot. 
A stalk rot and wilt of potato plants caused by Sclerotinia sclero - 
tiorum has been studied and described in Europe for several years. 
Pethybridge {22) observes that although the plants may be seriously 
affected in certain seasons, the tubers are not decayed. He made 
mention of the supposition that the fungus could not grow at all 
on potato tubers, but in 1909 and 1910 he obtained growth and 
development of sclerotia on slices of living tubers when he inoculated 
them with a pure culture of S. sclerotiorum obtained from ascospores. 
In America, so far, the Sclerotinia disease of potato plants is 
of minor importance. The writer has worked with only two cultures 
that were isolated from potato plants. 7 8 9 One of these was isolated from 
Florida plants, and the other from potatoes affected with a stalk decay 
in New Brunswick, Canada. Both of these cultures appear to be S . 
libertiana . In 1921, Lachaine {19) found 10 per cent of the potatoes 
in a field in New Brunswick affected with a stem rot and wilt. The 
causal organism was found to be a sclerotia-forming fungus which he 
was inclined to call S. libertiana. The crustlike formation of sclerotia 
on carrot, and the small sclerotia formed on potato agar as shown in 
his photographs, however, are very similar to those produced by S. 
minor. 
The inoculation of beets was very largely unsuccessful or doubtfully 
positive, in many cases. No marked amount of decay was obtained 
with any strain, but in some cases the brownish discoloration and 
decay entered deep enough so that the fungus could be reisolated 
from the inner tissues. When the reisolations were successful the 
inoculation is marked positive in the table, but when only a slight 
discoloration and surface growth of the fungus was evident the 
experiment is marked with a question mark. 
It is readily apparent, in so far as the cross-inoculation studies 
herein listed are concerned, that the host range of Sclerotinia spp. 
is so wide that it is impossible to separate the different species on the 
basis of host infection. On the hosts tried— S. libertiana , S. minor? 
S. ricini? and S. intermedia —all produced definite infection and decay, 
as shown in Table Y. On most host plants the type of decay pro¬ 
duced by the above species is quite similar and it is not until peculiari¬ 
ties of mycelial growth become evident or sclerotial formation takes 
place that the species can be distinguished (pi. 5 A, B, C, D, and E). 
While there were slight variations from time to time between 
the growth and appearance of the S. libertiana strains obtained from 
different hosts, there were no more differences than those occasioned 
by fluctuations in temperature and humidity when the same strain 
was used in separate experiments. All observations and experiments 
conducted thus far indicate that all of the large sclerotial forms 
under observation belong to the same species. With the exception of 
7 Potato cultures were obtained through courtesy of H. H. Whetzel, of Cornell University, Ithaca, N. Y. 
8 Cultures from lettuce by Ivan C. Jagger and W. S. Beach; from sunflower, by C. E. Owens; and from 
yarrow, by H. A. Edson. 
9 Culture by G. H. Godfrey. 
