Mar. 15, 1925 
Degeneration Diseases of Potatoes 
507 
plant was tested with rugose mosaic in 
.series 5 to 9. The remaining series 
represent inoculations comparable with 
similar series conducted in cages, the 
results of which will be noted later. 
The current-season effects of these inoc¬ 
ulations are represented in Table V. 
From the data on series 5 to 9 it is 
apparent that inoculum from either 
the entire shoots, the stems and peti¬ 
oles, or the leaflets alone, was more 
effective than that from roots or tubers; 
in fact, the very low percentage of in¬ 
fection that followed inoculations from 
roots or tubers may perhaps be due to 
field infection, although the uninocu¬ 
lated controls in these series remained 
healthy. The practically negative re¬ 
sults from the inoculation with juice 
from the seed tubers is somewhat sur- 
ising, considering the facts that they 
erpetuate the disease and that grafting 
causes infection. These seed tubers 
were unplanted ones from the same lot 
as those from which the plants were 
grown that served as the source of 
inoculum for series 5 to 8; the whole lot 
came from diseased stock and all that 
were planted produced diseased plants. 
Inoculation with juice from the roots 
also gave practically negative results, 
although they were taken from the 
same plants as the shoots, leaflets, and 
stems and petioles, showing that not all 
parts of a plant contain the virus in 
a similar state of infectiousness. In¬ 
fectiousness here seems to be correlated 
with the presence of chlorophyll. Not 
only were the colorless parts far less 
infective, but the inoculum from the 
leaflets was more infectious than that 
from the supporting parts of the plant, 
the latter infecting only 75 per cent of 
the plants inoculated instead of all of 
them. Also the inoculum from the 
leaflets was more infectious than that 
from the leaflets, petioles, and stems 
(aerial parts) combined, because, while 
infecting no more plants, still it infected 
them more completely by August 14, 
as is shown by Figure 1. As this figure 
indicates, of the 20 plants infected from 
the leaflets (in section W-7, row 2), 
16 were obviously diseased in the 
upper leaves of all the shoots by August 
14, while of the 20 plants infected from 
the shoots (in row 4), only 9 were 
thus affected. The inoculum was used 
from an uncovered dish; possibly when 
present chlorophyll prevented a sterili¬ 
zation of the inoculum by light. 
Inoculations with mild mosaic (in 
series 14 of Table V) induced the ap¬ 
pearance of no current-season symp- 
Table V .—Leaf mutilation inoculations of Green Mountains in the open field 
in 1923 
Inoc¬ 
ula¬ 
tion 
series 
No. 
Source of inoculum 
Inoculated plants 
Uninoculated 
controls 
Variety 
Symptoms 
Total 
num¬ 
ber 
Num¬ 
ber 
in¬ 
fected 
| 
Symptoms 
Num¬ 
ber 
of 
I hills 
i 
1 
Symp¬ 
toms 
1922 
Progeny, 1923 
5 
Green Moun¬ 
Rugose mo¬ 
Rugose mosaic, 
10 
1 
Rugose mosaic_ 
i 30 
Healthy. 
tain. 
saic. 
roots. 
! 
6 
_do_ 
_do_ 
Rugose mosaic, 
20 
20 
_do_ 
20 
Do. 
leaflets. 
l 
7 
_do_ 
_do_ 
Rugose mosaic, 
20 
15 
-do_ 
! 20 
18 hills 
stems and pet¬ 
healthy. 
ioles. 
8 
_do_ 
_do_ 
Rugose mosaic, 
20 
20 
1 20 
Healthy. 
shoots. 
9 
_do_ 
_do_ 
Seed tubers_ 
16 
2 
_do_ 
24 
Do. 
10 
_do . 
Healthy_ 
Healthy_ 
17 
0 
Healthy_ 
19 
Do. 
14 
_do_ 
Mild mosaic. 
Mild mosaic_ 
10 
0 
Apparently healthy 
10 
Do. 
16 
_do_ 
Leaf-rolling 
Leaf-rolling mo¬ 
10 
10 
Leaf-rolling mosaic. 
10 
Do. 
mosaic. 
saic. 
18 
_.do.- - 
Rugose mo¬ 
Rugose mosaic.. 
5 
5 
Rugose mosaic_ 
15 
Do. 
saic. 
20 
_do 
Streak_ 
Streak and slight 
5 
1 
Streak.. . . __ 
15 
Do. 
mottling. 
22 
do 
Healthy 
Healthy _ 
10 
0 
Healthy . . . 
30 ! 
Do. 
29 
Irish Cob¬ 
Mild mosaic (?). 
10 
0 
_do_ 
30 
Do. 
bler. 
30 
do 
Rugose mosaic 
5 
5 
Rugose mosaic in¬ 
15 1 
Do. 
with streaking. 
cluding streaking, 
spotting and 
| 
burning. 
31 
do 
. ..do_ 
10 
8 
Rugose mosaic in 6 
30 
Do. 
hills. Rugose 
mosaic including 
j 
streaking, spot¬ 
ting and burning 
J 
i 
in 2 hills. 
j 
