A NEW TYPE OF ORANGE-RUST ON BLACKBERRY* 
By B. O. Dodgb 
Pathologist, Fruit-Disease Investigations , Bureau of Plant Industry , United States 
Department of Agriculture 
The writer in discussing the distribution of the orange-rusts of Rubus 3 
referred to certain blackberries obtained at Forestville, Md., in 1922. 
Some of the plants were infected with the typical short-cycled form, one 
plant with the long-cycled Gymnoconia, and two plants with a form 
whose spores were reddish orange and corresponded in other particulars 
to aecidiospores of the long-cycled rust. When spores from these two 
particular plants were sowed on agar, they germinated so quickly and 
with such long germ tubes that the rust was at first marked as long 
cycled. Examination of the plates a day or two later, however, dis¬ 
closed large numbers of long promycelia bearing sporidia. On repeating 
the germination test, the same results were obtained. Any long germ 
tubes that persisted were ignored, or assumed to be abnormal. The 
presence of hundreds of promycelia could not be overlooked. The 
appearance of the rust being so like that of the ordinary Gymnoconia 
and the manner of spore germination so puzzling, a more critical study 
of this strain of the rust was made in 1923, when the plants were in far 
better condition for spore production than they had been just after being 
transplanted the previous year. The results of the later investigation 
show that three plants are infected with what might be called an inter¬ 
mediate form, because some aecidia are short cycled and others long 
cycled. 3 It is interesting to find here an example which can be best 
described as a short-cycled rust being derived from a long cycled form. 
On April 11, 1922, 12 infected wild blackberries, No. 288-299, were dug 
up in a pasture at Forestville, Md.; two plants, No. 290 and 294, died 
soon afterwards. A brief account of this collection of rusted plants may 
serve to bring out more clearly the true nature of our Rubus orange- 
rusts. 
If one plant is infected with the long-cycled rust, and another with 
the short-cycled, aecidia will usually, other conditions being equal, 
mature about a week or 10 days earlier on the latter plant. After the 
10 surviving plants in this collection were brought to the greenhouse 
from the cold frames, March 10, 1923, the date of the maturing of the 
first aecidia on each was noted. Within three weeks aecidia had matured 
on six plants. The aecidia on five plants were yellowish orange in 
color, and their spores produced regular promycelia. This is certainly 
our common short-cycled blackberry rust. The rust on No. 297 needs 
further study. About 10 days later aecidia matured on the other four 
plants. Germination tests were made of spores from several leaves 
from No. 291 and no promycelium was found. The rust on this plant 
is typically long-cycled, and is of no particular interest in itself. 
It was not until we had improved our methods of testing spore germi¬ 
nation that we discovered that the rust on the other three plants was 
1 Accepted for publication June as. 1933. 
* Dodge B. O. the distribution or the orange-rusts or rubus. In Phytopathology, v. 13, p. 61-74. 
1933. Literature cited, p. 74- 
* For convenience may we not refer to an aecidium as “short cycled” if its spores produce promycelia, 
and as “long cycled” if they produce germ tubes on germination? 
Journal of Agricultural Research, 
Washington, D. C. 
agm 
Vol. XXV, No. zs 
Sept. 32, 1933 
Key No. G —329 
(49 r ) 
