JOURNAL OF AGMQILTffiAL RESEARCH 
Vou XXV Washington, D. C., August 4, 1923 No. 5 
SYSTEMIC INFECTIONS OF RUBUS WITH THE ORANGE- 
RUSTS 1 
By B. O. Podge 
Pathologist , Fruit-Disease Investigations, Bureau of Plant Industry, 
United States Department of Agriculture 
INTRODUCTION 
Cultivation of some of the most desirable varieties of blackberries and 
raspberries has been limited or discontinued in certain regions because 
of the orange-rusts which inhibit the development of fruit on the canes 
infected. Local infection of leaves of blackberries by sowing aecidio- 
spores of the long-cycled orange-rust, Gymnoconia, has been brought 
about by a number of persons. Reference to such work as has been done 
along this line has been made by Clinton (j, 4) 2 and Kunkel (7). 
The problem of working out practical methods for the control of these 
rusts, however, depends upon a knowledge of when and how the gameto- 
phytic mycelium enters the host and becomes established as a constitu¬ 
tional parasite. The results of infection experiments dealing with this 
problem are reported at this time. 
The common blackberry has perennial roots from which canes arise 
year by year, those of one year bearing fruit the next. The turions 
appear in the spring from the buried crown or from root runners and 
become the “old canes” of the next year, dying after fruiting. The new 
canes are of the type having indefinite growth; therefore the formation 
of a terminal bud which would remain dormant during the winter and 
push out into new growth the following spring would be very unusual 
and abnormal, although lateral buds at the lower part of the old cane 
frequently develop into new branches. The crown usually lies a few 
inches beneath the surface of the soil, and consequently there is a part 
of the original cane which lives several years. As new shoots and roots 
arise from this structure it loses its identity. Nurserymen would refer 
to that part of the cane beneath the soil simply as the crown because 
new canes arise in this region. It may also be referred to as the per¬ 
ennial base. Figure 1 shows these features diagrammatically for a sim¬ 
ple plant (see also fig. 5). The structure of the cane and the relation of 
its tissues as they appear in cross-sections are brought out in Plate 2, B. 
HOST PARASITE RELATIONS 
In dealing with a rust which is perennial and systemic in a woody 
plant, it is desirable to be familiar with the appearance and distribution 
of the mycelium. The sporophytic hyphae of the Gymnoconia are con- 
1 Accepted for publication May 2, 1923. 
* Reference is made by number (italic) to “literature cited," p. 242. 
Journal of Agricultural Research, 
Washington, D. C. 
afv 
Vol. XXV No. 5 
Aug. 4, 1923 
Key No. G-322 
54483—23 - 1 
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