Mar. 15, 1925 
Degeneration Diseases of Potatoes 
509 
toms, which is in marked contrast to 
the complete positive results obtained 
with leaf-rolling and rugose mosaic in 
the open (series 8, 16, and 18) and with 
mild mosaic in cages (described later). 
In series 29, a mild type of mottling, 
tentatively called a mosaic, on Irish 
Cobblers likewise failed to produce 
current-season symptoms on inocu¬ 
lated Green Mountains. Negative re¬ 
sults with a similar type of so-called 
mosaic on Irish Cobblers were obtained 
with stalk grafts on 12 Green Mountain 
shoots in three separate tuber units in 
cages. This seems to suggest that the 
mottling on the Irish Cobblers is not 
infectious, but to verify this conclusion 
similar negative reactions in the second 
generation are essential. In any case 
this mottling on Irish Cobblers appears 
distinct from rugose mosaic, as de¬ 
scribed previously and as disclosed by 
the positive current-season reactions in 
series 30 and 31; in these series almost 
100 per cent infection resulted from 
rugose mosaic inoculations performed 
under the same conditions as for the 
mottled Irish Cobbler inoculation. 
In connection with the use of juice 
from seed tubers as described above, the 
results of tests of knife transmission 
may be noted. The use of the same 
knife to cut alternated diseased and 
healthy tubers at planting time, with 
10 healthy tubers thus inoculated with 
each disease, did not result in transmis¬ 
sion. Each of the four types of mosaic, 
spindle tuber, unmottled curly dwarf, 
leaf-roll, and several combinations were 
tested. 
INTERVARIETAL LEAF MUTILATION IN¬ 
OCULATIONS IN INSECT CAGES 
In order to determine the compara¬ 
tive reactions of the Green Mountain, 
Irish Cobbler, and Rural New Yorker 
varieties to mild, leaf-rolling, and ru¬ 
gose mosaic, and of Green Mountains 
to streak, leaf mutilation inoculations 
were performed in insect cages in 1923. 
Inoculations with mosaic were made on 
the same date, when the height of the 
plants varied from 7 to 30 cm. Dis¬ 
eased Green Mountains served as the 
sources of inoculum. The method of 
planting three hills in each cage, from 
three tuber units, respectively, resem¬ 
bled that previously described for cage 
experiments. The current-season re¬ 
sults of these inoculations are recorded 
in Table VI. 
From the results presented in Table 
VI it is quite apparent that rugose 
mosaic in series A-3, B-3, and C-3 
produced complete infection in the 
three varieties. Inoculations with mild 
and leaf-rolling mosaic were equally 
effective on Green Mountains (pi. 6, A) 
but not apparently so on Irish Cobblers 
and Rural New Yorkers. 11 It is also 
noteworthy that the first symptoms of 
mild mosaic, leaf-rolling mosaic, and 
rugose mosaic appeared, respectively, 
32, 25, and 18 days after inoculation, 
indicating different incubation periods- 
for these mosaic types. The absence 
of current-season symptoms with mild 
mosaic on Irish Cobblers and Rural 
New Yorkers suggests either differences 
in varietal susceptibility or varietal 
modification of symptoms of this dis¬ 
ease. Reactions resulting from aphid 
inoculations have been recorded. 12 
Table VII in this paper gives the data 
from later work. Streak was trans¬ 
mitted to Green Mountains resulting 
in the characteristic current-season 
symptoms (pi. 2, B). 
INTERVARIETAL INOCULATIONS WITH 
APHIDS 
For comparison with the leaf-muti¬ 
lation inoculations described in the pre¬ 
ceding section of this paper, inocula¬ 
tions were performed with aphids in 
insect cages in the field in 1923. Aphids, 
Macrosiphum solanifolii Ashm., ob¬ 
tained from rose bushes, were trans¬ 
ferred to healthy Bliss Triumphs and 
then to Green Mountains affected re¬ 
spectively with different types of mo¬ 
saic. After feeding for about 10 days 
on diseased plants, approximately 50 
to 100 aphids per hill were introduced 
to healthy caged plants varying in 
height from 7 to 30 cm. After feeding 
from 12 to 13 days on the inoculated 
plants the aphids were killed with nico¬ 
tine sulphate spray. Current-season 
reactions are recorded in Table VII. 
As is shown in Table VII, of the 
three varieties, Green Mountain, Irish 
Cobbler, and Rural New Yorker, that 
were tested, only the Green Mountain 
showed positive results with mild and 
leaf-rolling mosaic. All three varieties 
showed slight symptoms resulting from 
inoculations with rugose mosaic. How¬ 
ever, the reactions to rugose mosaic 
were not so pronounced as those with 
the leaf mutilation inoculations denoted 
in Table VI. No current-season symp- 
11 Since the submittal of this manuscript observations on the second generation disclosed mild mosaic 
on Rural New Yorker and leaf-rolling mosaic on Irish Cobbler and Rural New Yorker. 
1 2 Schultz, E. S., and Folsom, D. Op. cit. p. 65-84. 
