526 
Journal of Agricultural Research 
Vol. XXX, No. 6 
(3) Intervarietal leaf-mutilation in¬ 
oculations of Green Mountains trans¬ 
mitted mild mosaic and crinkle mosaic 
from Bliss Triumphs; leaf-rolling mo¬ 
saic, rugose mosaic, spindle tuber, and 
unmottled curly dwarf from Rurals; 
rugose mosaic from seedling lots; and 
leaf-rolling mosaic, rugose mosaic, and 
spindle tuber from Irish Cobblers. 
Varietal modification of symptoms was 
disclosed, mottling especially being sup¬ 
pressed by Rurals and Irish Cobblers. 
(4) Intervarietal leaf-mutilation in¬ 
oculations in insect cages showed that 
a repetition of the inoculation favors 
infection with mild mosaic and spindle 
tuber; that every one of several vari¬ 
eties was susceptible to spindle tuber; 
that Irish Cobblers either are symptom¬ 
less carriers of mild mosaic or are 
resistant or immune to this disease; 
that “mosaic dwarf” sometimes is a 
combination of rugose mosaic, spindle 
tuber, and streak; that there is a 
varietal difference in susceptibility to 
streak; and that with conditions ap¬ 
parently similar not only will results of 
inoculations sometimes be negative 
where experience would lead one to 
expect infection, but there even may be 
a separation of viruses originally in 
combination in a given inoculum. 
(5) Aphids sometimes do not trans¬ 
mit disease under conditions that ap¬ 
parently are the same as those giving 
positive results. 
(6) With regard to current-season 
symptoms, a progressively smaller 
amount of infection was induced by 
leaf-mutilation inoculation with the 
leaflets, entire shoots, stems and 
petioles together, seed tubers, and roots, 
respectively, of rugose mosaic plants. 
Similar inoculation with juice from 
mild mosaic Green Mountain shoots 
and from certain mottled Irish Cob¬ 
bler shoots, and the use of the latter in 
grafts, produced no apparent effects. 
Inoculation with the seed-cutting knife 
gave negative results with seven dis¬ 
eases and several combinations. 
(7) Leaf mutilation inoculations in 
insect cages produced current-season 
symptoms in Green Mountains with 
progressively shorter incubation pe¬ 
riods for mild mosaic, leaf-rolling 
mosaic, and rugose mosaic, but only 
rugose mosaic induced current-season 
symptoms in Rural New Yorkers and 
Irish Cobblers. Since these varieties 
are susceptible to leaf-rolling mosaic, 
this shows for this disease either a 
longer incubation period or a lower 
degree of varietal susceptibility cor¬ 
related with varietal suppression of 
mottling. 
(8) Aphid inoculations in insect 
cages produced current-season symp¬ 
toms in Green Mountains with four 
types of mosaic—mild, leaf-rolling, 
rugose, and crinkle mosaic. Here the 
current-season symptoms of rugose 
mosaic following aphid inoculation 
were less marked than after parallel 
leaf-mutilation inoculations, which 
was also true in Rural New Yorkers 
and Irish Cobblers. Mild mosaic in 
at least the eighth consecutive genera¬ 
tion of a Green Mountain strain was 
still mild and was distinct from rugose 
mosaic and the other types, contrary 
to prevailing theories of progressive 
increase in severity that apparently are 
based on general field observations 
made where the more severe types can 
increase. Facilitation of experimenta¬ 
tion is obtained from the use of insect 
cages with openings in the top. 
(9) Other aphid inoculations pro¬ 
duced, in addition, current-season symp¬ 
toms of three disease combinations— 
rugose mosaic and spindle tuber, 
crinkle mosaic and spindle tuber, and 
leaf-rolling mosaic and leaf-roll. 
(10) Root and foliage contact with 
spindle tuber plants under insect-free 
greenhouse conditions resulted in no 
transmission. In another greenhouse, 
contact of roots and leaves, and of 
leaves in the absence of aphids and leaf 
mutilation but in the presence of other 
kinds of insects, was accompanied by 
the dissemination of mosaic but not of 
leaf-roll. 
(11) A third species of aphids, the 
“buckthorn aphid” (Aphis abbreviata 
Patch), has been found to be common 
on potatoes and to be capable of trans¬ 
mitting mild mosaic, at least. Its early 
appearance has been accompanied by 
EXPLANATORY LEGEND FOR PLATE 10 
A. —The two middle rows are progeny of Green Mountains planted in Virginia between leaf-roll rows 
(left) and between mosaic rows (right). Photographed on August 18,1923. For disease percentages see 
Table XI. For progeny of originally similar lots planted elsewhere see Plate 10, B, C, and D 
B. —The two middle rows are progeny of Green Mountains planted on Long Island between leaf-roll 
rows (right) and somewhat isolated (left). Photographed on August 18, 1923. For disease percentages 
see Table XI. For progeny of originally similar lots planted elsewhere see Plate 10, A, C, and D 
C. —The middle row is progeny of Green Mountains planted on Highmoor Farm in southwestern 
Maine between leaf-roll rows (in foreground) and between mosaic rows (beyond stake). Photographed on 
August 18, 1923. For disease percentages see Table XI. For progeny of originally similar lots planted 
elsewhere see Plate 10, A, B, and D 
D. —The middle row beyond the gap in the foreground is progeny of Green Mountains planted on 
Aroostook Farm between leaf-roll rows. Photographed on August 18, 1923. For disease percentages see 
Table XI. For progeny of originally similar lots planted elsewhere see Plate 10, A and C 
