VoL. XXIV Washington, D. C., June i6, 1923 No. ii 
MORPHOLOGY AND HOST RELATIONS OF 
PUCCINIASTRUM AMERICANUM ‘ 
By B. O. Dodgb 
Pathologist, Fruit-Disease Investigations, Bureau of Plant Industry, United States 
Department of Agriculture 
The orange rusts have always been considered as practically the only 
rusts of economic importance on species of Rubus in America. Kuehneola 
uredinis, it is true, is known to cause considerable damage to fruiting 
canes of certain cultivated varieties of blackberries. Pucciniastrum 
americanum (Farl.) Arth. is not rare on wild raspberries but its effects on 
the host have been found heretofore to be altogether negligible. Brief 
notes dealing mostly with its relationships to the European form P. arc- 
ticum have appeared from time to time but no reference has been made 
to damage to cultivated raspberries. An outbreak of this rust, therefore, 
of such severity as to cause defoliation and spotting of canes of certain 
varieties, becomes a subject of interest. 
One of the native hosts of this rust is the wild Rubus strigosus, and like 
the orange-rusts and the stemrust, Kuehneola, the Pucciniastrum will 
no doubt be found wherever the natural hosts may grow. The rust has 
been reported rarely on R. occidentalis, but “P. neglectus,'* a hybrid 
between the red and the black raspberries, seems to be rather susceptible 
according to Farlow {9, p. 13).^ At Bell, Md., where an outbreak 
occurred in 1922, Mr. G, M. Darrow has gathered together from all parts 
of the world a number of species and horticultural varieties of Rubus 
and has originated many new forms in connection with his breeding 
work. During July it was found that the leaves of several different 
hybtids were dropping off prematurely, leaving the canes entirely bare 
below. The lower surface of the leaves was evenly covered with uredo- 
spores, giving them nearly the same appearance as blackberry leaves 
heavily infected with the Kuehneola. The leaves at the growing tips 
were sometimes only slightly affected and the attacks seemed to increase 
in severity from the tips downward, showing that the rust had been 
present for some time. 
Conical peridia (PI. i, C), each surmounted by a corona, were easily 
found on leaves just being attacked, and as the spores were identical with 
those found on the fallen leaves there can be no question that this defolia¬ 
tion was being caused by what has heretofore been considered a harmless 
rust. From July 28 to August 4 a smwey was made to ascertain which 
species, varieties, and hybrids were being attacked. Mr. Darrow coop¬ 
erated with the author in going over these records. 
1 Accepted for publication Jan. 22, 1923. 
’ Reference is made by number (italic) to “Literature cited,” pp. 893~894, 
Journal of Agricultural Research. Vol. XXIV, No. ii 
Washington, D. C. June 16, 1923 
aew Key No. G-311 
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