Mar. 15, 1925 
Degeneration Diseases of Potatoes 
521 
This is also indicated by the spread to 
the second row. There was no shoot 
contact early enough to permit the pos¬ 
sibility of transmission by such means. 
That the disease spread in the plot in 
1923 and was not perpetuated in the 
tubers from 1922 is indicated by the 
difference between the first and second 
rows on the north and by the absence 
of any rugose mosaic in the third row 
on the north and also nine rows (fig. 1, 
sec. W-6) planted elsewhere with tubers 
from the same healthy stock. Further¬ 
more, other parts of the same healthy 
stock that were inoculated artificially 
as early in 1923 as diseased plants were 
available became diseased at about the 
same time and in the same way, except 
with a higher percentage of incidence. 
Whether rugose mosaic was spread 
here by means of flea beetles ( Epitrix 
cucumeris Harris), tarnished plant bugs 
(Lygus pratensis L.), or aphids, is open 
to question. Aphis ahhreviata was ob¬ 
served here at the time of securing the 
inoculum for the artificial inoculations. 
However, roguing in another seed-plot, 
somewhat isolated, before any aphids 
were present and while flea beetles and 
tarnished plant bugs were present, did 
not result in the elimination of mosaic 
•of the mild type. Transmission by flea 
beetles ( Psylloides affinis), capsid bugs 
(Calocoris bipunctatus) , and jassids 
(Typhlocyba Ulmi) has been demon¬ 
strated for leaf-roll by Murphy. 18 
In the same disease propagation plot 
there was also some spread of leaf-roll¬ 
ing mosaic, but only to the adjoining 
healthy row on the north, with the 
symptoms (pi. 9, B and C) appearing 
later than for rugose mosaic, in accord¬ 
ance with the results described pre¬ 
viously, showing that rugose mosaic, 
leaf-rolling mosaic, and mild mosaic 
have progressively longer incubation 
periods. Contrary to what might be 
•expected from these differences in the 
length of the incubation period, ex¬ 
perience has shown that rugose mosaic, 
leaf-rolling mosaic, and mild mosaic are 
progressively more easily transmitted 
in the field from diseased to healthy 
plants (see Tables I and II). 
These facts not only indicate that 
three types of mosaic may be spread in 
the field, but also confirm the theory 
previously advanced 19 that rugose mo¬ 
saic may appear as partial infection of 
hills and tuber units as the result of 
uncontrolled field transmission occur¬ 
ring during the same season. Such 
current-season symptoms, as well as 
the incomplete or partial infection of 
the tuber, followed by a delayed mani¬ 
festation of symptoms or by incom¬ 
plete infection, often include spotting, 
streaking, and leaf-dropping (pi. 8, 
C and D). 
TEST OF MOSAIC PERPETUATION 
THROUGH TRUE SEEDS 
In 1921 the tubers and seed balls 
were saved together from each of a 
number of Green Mountain hills in a 
commercial field which contained about 
5 per cent mild mosaic and which was 
infested with aphids. Some of the 
hills in question were mosaic and some 
were apparently healthy. The tubers 
were planted in the Orono, Me., green¬ 
house during the following winter and 
the seeds were planted in the same 
place in steam-sterilized soil. Seed¬ 
lings were started in the winters of 
1921-22 and 1922-23 and their first 
tubers were planted to produce a 
second generation. Of the original 
field-selected hills, hills 1 and 2 were 
mosaic in the field and produced, re¬ 
spectively, 2 and 3 mosaic tubers, and 7 
healthy seedlings and no seedlings; 
hills 3 and 4 produced, respectively, 2 
and 1 mosaic tubers, and 27 and 40 
healthy seedlings; hill 5 produced 1 
mosaic and 2 healthy tubers, and 6 
healthy seedlings; hill 6 produced 2 
healthy tubers and 32 healthy seedlings. 
Most of the seedlings in the second 
generation resembled Green Moun¬ 
tains closely, and were healthy in re¬ 
gard to the foliage. In brief, 1 mosaic 
plant (hill 1) produced 7 healthy seed¬ 
ling progeny while 3 apparently healthy 
plants (hills 3, 4, and 5) contracted 
mosaic which showed in their tuber- 
progeny but not in any of their 83 
seedling-progeny. 
EFFECT OF DIFFERENT CLIMATIC 
CONDITIONS IN 1922 ON MOSAIC 
LOTS FROM THE SAME TUBERS, 
AS SHOWN BY THE PROGENY 
GROWN IN NORTHEASTERN 
MAINE IN 1923 
In order to ascertain the effect of 
climatic conditions on mosaic, seed 
pieces from the same tuber were planted 
in 1922 in three regions, namely, on 
Aroostook Farm in northeastern Maine, 
at Riverhead, Long Island, and at Nor- 
is Murphy, P. A. investigations on the leaf-roll and mosaic diseases of the potato. Jour 
Dept. Agr. and Tech. Instr. Ireland 23: 20-34, illus., 1923. 
- ON THE CAUSE OF ROLLING IN POTATO FOLIAGE; AND ON SOME FURTHER INSECT CARRIERS OF THE 
.leaf-roll disease. Sci. Proc. Roy. Dublin Soc. (n. s.) 17: 163-184, illus., 1923. 
19 Schultz, E. S., and Folsom, D. Op. cit. p. 97 . 
