Aug. 4, 193 3 
Systemic Injections of Rubus with Orange-Rusts 
241 
(2) The roots and rootlets of the black raspberry are attacked by the 
hyphae, mycelium being found not only along the rays but very generally 
in the wood ring and along the cambium and phloem. As in the dew¬ 
berry, the mycelium does not follow the roots for very great distances. 
Hyphae have been found in roots 8 or 10 inches long. 
(3) Canes of a thoroughly infected black raspberry do not root at 
the tips very readily; therefore the long-cycled rust is not so often 
spread vegetatively to tip plants from an infected parent. The infection 
of very young tip plants by sporidia from teleutospores largely accounts 
for the appearance of the rust on new plants. The wild raspberry, 
Rubus occidentalism and the horticultural varieties, Plum Farmer and 
Cumberland, were infected by laying black raspberry leaves bearing 
teleutospores over rooting tips of stolons and maintaining suitable 
moisture conditions. Infections of the black raspberry also occurred 
when the teleutospores were taken from blackberry leaves. 
(4) Susceptible blackberries can be infected with the short-cycled 
rust by sowing the sporidia formed on promycelia from germinating 
aecidiospores on young root shoots; 150 separate primary infections were 
made in this way. If a blackberry cane has been primarily infected by 
sowing sporidia, the hyphae of the rust will be found in most cases to be 
confined to the cambium and phloem tissues. Only rarely do hyphae 
become established in the tip of an inoculated shoot and grow up with 
the cane as does the mycelium in a cane from an infected hill. Localized 
gametophytic primary infections which do not become permanently estab¬ 
lished sometimes occur, especially if the young cane is several inches high 
when inoculated. A cane primarily infected usually blossoms normally 
except at the infected nodes, but canes arising from an infected hill and 
having mycelium in the growing regions from the beginning do not 
blossom. Certain nodes may happen to escape invasions by hyphae; 
in this case blossoms will develop. 
(5) Measures for controlling the orange rusts are suggested, emphasis 
being laid on a thorough inspection of nursery stock for at least one month 
after planting, and the complete eradication of plants showing rust. 
Primary infections of blackberry from sporidia are very characteristic and 
at first do not involve the whole plant and its root system. A limited 
amount of the root directly connected with the infected cane will usually 
have been invaded by the hyphae from above, so the destruction of this 
old cane with a few inches of the root will be sufficient. If such canes 
are allowed to grow, the parasite soon becomes established in the root 
crown and it will then be necessary to uproot and destroy the whole 
plant. As a matter of safety in every case the infected canes and all 
attached reots should be destroyed. 
(6) The infection experiments prove: (a) That the short-cycled rust on 
wild blackberry can infect such cultivated varieties as the Kittatinny, Ice¬ 
berg, Mercereau, Crandall, Taylor, Blow r ers, Ancient Briton, etc.; (b) that 
the sporophytic .stage of the Gymnoconia w r ill go over from the mountain 
blackberry, Rubus canadensis , to such varieties as the Ward, Taylor, Mer¬ 
cereau, and Loganberry, and that teleutospores can be obtained on leaves 
of certain blackberries and dewberries by sowing aecidiospores from the 
black raspberry, which can in turn be likewise infected by sowing aecidio¬ 
spores from the blackberry; (c) that the black raspberry can also be sys- 
temically infected with sporidia from teleutospores of the long-cycled rust 
on blackberry. 
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