604 
Journal of Agricultural Research 
Vol. XXVIII, No. 6 
Windsor sweet cherries from northern Michigan and on Montmorency (sour) 
and Early Richmond (sour) cherries from southern Michigan. The symptoms 
on sour and sweet cherries are decidedly dissimilar. 
On the sweet cherry the rot is characterized by a firm, brown, cone-shaped 
mass extending in toward the pit. This firm, brown mass is made up of dead 
host cells interpenetrated and apparently held together by the fungous mycelium. 
It is firmer than the surrounding tissue, and if the skin that covers it be carefully 
broken the 'affected tissue beneath can often be lifted out intact. The skin 
which overlies the affected area is covered with an olive-green growth of sporu- 
lating mycelium; sometimes, however, this sporulating layer is hidden under a 
mass of white, fluffy mycelium. 
The symptoms on sour cherry are quite different. The only similarity, in fact 
is the olive-green layer of sporulating mycelium growing on the epidermis, and 
even this soon becomes soaked with juice and looks black and matted. In the 
early stages of the disease there is apparently so little penetration of the myce¬ 
lium below the epidermis that the whole surface of a cherry may be covered with 
the olive-green growth before the flesh is decayed near the pit. When the tissue 
decay does take place, it is light brown and not nearly so firm as that in the 
sweet cherry. No fluffy growth of mycelium has been observed on sour cherries 
by the writers. In general, the disease on sour cherries is characterized by a 
decayed epidermis covered with a black, water-soaked mat of sporulating myceli¬ 
um. The stem of the decayed cherry is almost invariably dead and often con¬ 
tains fungi apparently saprophytic, notably Cladosporium sp. and Botrytis sp. 
The olive-green decay is caused by Alternaria sp., which apparently enters 
through wounds in the cherry. These wounds during 1923 consisted mainly of 
cracks, the cause of which is entirely problematical. It is possible they were rain 
cracks, though certain circumstances suggest that they may arise in transit. 
The question is one which needs further investigation. Numerous isolations 
were made from collected specimens and several different organisms were obtained, 
namely, unidentified species of Rhizopus, Penicillium, Botrytis, Mucor, As¬ 
pergillus, and Cladosporium. Most of these organisms proved pathogenic, but 
lesions like those described above, particularly those described for sweet cherries, 
were produced only by inoculations with the Alternaria obtained from diseased 
cherries. There is no definite proof that the species of Alternaria isolated from 
the two kinds of cherries are identical. Cross-inoculations have shown, however, 
that the Alternaria from sweet cherries is pathogenic to sour cherries, and vice 
versa. 
Inoculation experiments were set up as follows: The stems, which were usually 
dead and contained various species of fungi, were clipped and the cherries were 
sterilized in a 1 to 1,000 solution of mercury bichlorid, or in 50 per cent alcohol, 
for 5 to 30 minutes. They were then rinsed in sterilized tap water and placed in 
large sterile Petri dishes. Inoculations were made either (1) by forcing mycelium 
from an agar culture of Alternaria into the flesh of the cherries with a sterile needle, 
or (2) by merely laying fragments of mycelium on the surface of uninjured cherries. 
Infection was obtained in each of several hundred inoculations made by the first 
method and always resulted in lesions like those described above; from these 
lesions, on both sweet and sour cherries, an Alternaria was reisolated which was 
apparently identical with the one used for inoculation. No infection resulted 
from inoculations made by the second method. Failure to obtain it is taken to 
mean that the fungus is unable to penetrate the uninjured skin of the fruit. No 
infection developed on the controls, which consisted of wounded and unwounded 
cherries previously sterilized in the manner already described. All experiments 
were conducted at room temperature. 
