584 
Journal of Agricultural Research v 0 i. xxvm, No. e 
During the course of the present study of this disease which has extended 
over the last six years the writer has frequently found this Sphaeropsis on dead 
currant canes, often in close association with B. ribis or its form, B. ribis chromo - 
gena. It was not, however, until the summer of 1923 that mature perithecia of 
this fungus were found on currant and the identity of this fungus with Physalos¬ 
pora malorum established by morphological and culture studies. 
ASSOCIATION OF THE PYCNIDIAL STAGE OF PHYSALOSPORA 
MALORUM WITH BOTRYOSPHAERIA RIBIS ON CURRANT 
CANES 
Dead currant canes, whether killed by cane blight or not, frequently bear 
mature pycnidia of Physalospora malorum . Mature pycnidia of P. malorum 
often occur in close association with both B. ribis and B. ribis chromogena , the 
pycnidia of which as explained in an earlier paper 7 are of the Dothiorella type. 
On currant canes, moreover, the superficial appearance of the fruiting bodies of 
the fungi is somewhat similar. So closely, indeed, are the fungi associated and 
so similar their general appearance that during the early stages of our work 
pycnidia of the Sphaeropsis type frequently occurred in sections prepared for 
microscopic study of the currant cane blight fungus. 
These considerations together with the fact that for several years only one 
type of ascospore was found on currant suggested the possibility that the “Sphae- 
ropsis-like” pycnidia might be a stage in the life history of the Botryosphaeria or 
at least that the Sphaeropsis might be parasitic on currant. Inoculation experi¬ 
ments on currants with cultures made from single spores of the Sphaeropsis 
from currant and from other hosts gave, however, uniformly negative results. 
This was true even under conditions which gave striking infections when the 
true parasite, Botryosphaeria ribis chromogena was used. These results agree 
with those of Grossenbacher and Duggar. 8 Moreover, although several hundred 
single spore cultures of the fungi from currant have fruited, no connection could 
be established between the pycnidia of the Sphaeropsis type and either spore 
form of B. ribis. These facts made it appear highly improbable that the Sphaerop¬ 
sis was a pycnidial form of the Botryosphaeria, Satisfactory proof of the dis¬ 
tinctness of the two fungi was, however, not obtained until the summer of 1923 
with the completion of the morphological and culture studies on Physalospora 
and Botryosphaeria on apple already reported 9 and the discovery of the as- 
cogenous stage belonging to the Sphaeropsis on currant. 
THE PERFECT STAGE OF THE SPHAEROPSIS ON CURRANT 
Although the perfect stage of the cane blight fungus as well as the saprophyte 
B. ribis, has frequently been collected during the past six years and hundreds of 
single spore cultures have fruited, ascospores which produced pycnospores of the 
Sphaeropsis type in culture have been found only once on currant. This was at 
North Rochester, Mass., where, on June 27, 1923, a single currant cane covered 
with mature perithecia was found in a pile of old currant prunings. This material 
was at once recognized by Miss Wilcox, who was at that time carrying on culture 
studies of the currant cane blight fungus and related fungi at Woods Hole as 
different from B. ribis and very similar to Physalospora malorum. Thirty-seven 
7 Shear, C. L., Stevens, N. E., and Wilcox, M. S. botryosphaeria and physalospora on cur¬ 
rant and APPLE. Jour. Agr. Research 28: 589-598, illus. 1924. 
« Grossenbacher, J. G., and Duggar, B. M. a contribution to the life-history, parasitism, 
and biology of botryosphaeria ribis. N. Y. State Agr. Exp. Sta. Tech. Bui. 18, p. 148. 1911. 
• Shear, C. L., Stevens, N. E., and Wilcox, M. S. botryosphaeria and physalospora on currant 
and APPLE Jour. Agr. Research 28: 589-598, illus. 1924. 
