Mar. 15, 1925 
Degeneration Diseases of Potatoes 
517 
respect duplicating conditions of the 
preceding winter in this greenhouse. 
Thrips were present as usual, being 
more abundant where the W series 
was grown. The plants in these series 
were observed frequently and the 
tubers when dug, on April 4, were also 
examined. Conditions for spindle 
tuber diagnosis were considered some¬ 
what unfavorable. The tubers were 
kept in cold storage during the sum¬ 
mer. The plants of the second gener¬ 
ation were grown in the latter months 
of 1923, one only from each tuber. The 
mosaic and leaf-roll observed in the 
two generations designated, respec¬ 
tively, because of the time of planting 
as those of 1922 and 1923, although 
both were grown in 1923, are given in 
Table IX. 
It will be seen from this table that 
about two-thirds of the Bliss Triumphs 
were mosaic, with one healthy 1922 
hill producing mosaic progeny. Of the 
Green Mountains, about two-thirds 
were grown in 1922 in root contact with 
Bliss Triumph mosaic hills, that is, 24 
of a total of 37. Of the 24, 5 produced 
mosaic progeny; and of the 37, 7 pro¬ 
duced mosaic progeny. The difference 
of 2 represents two plants in root- 
contact with leaf-roll Bliss Triumphs. 
None of the Green Mountains con¬ 
tracted leaf-roll. Evidently conditions 
were favorable for the spread of mosaic 
both with and without root contact, 
but not for the spread of leaf-roll. The 
abundance of mosaic plants and the 
arrangement of the plants made leaf 
contact with mosaic plants possible for 
the two Green Mountain hills that were 
not in root contact and that became 
mosaic. It will be noted that only one 
tuber (of only one hill, of course) be¬ 
came mosaic in the C series, where 
white flies were present. The greater 
number of infections occurring in the 
W series leads to the suggestion of the 
possibility of transmission by thrips; 15 
this difference, together with the fact 
that some of the 1922 hills had both 
diseased and healthy progeny, also in¬ 
dicates that the infection of the Green 
Mountains occurred in the greenhouse 
and was not present in the tubers when 
they were planted in 1922. Inasmuch 
as thrips can be controlled readily in 
experiments and have no practical im¬ 
portance as to potatoes, no tests are 
planned to test this suggestion about 
their transmitting potato mosaic. It 
remains clear, however, that mosaic 
can spread in the absence both of aphids, 
and of artificial inoculation. 
Table IX .—Effect of 'proximity to disease in the absence of aphids 
Number of hills, 
1922 
Number of hill 
lots, 1923 « 
Number of hills, 
1923 » 
To¬ 
tal 
Mo¬ 
saic 
Leaf- 
roll 
To¬ 
tal 
Mo¬ 
saic 
Leaf- 
roll 
To¬ 
tal 
Mo¬ 
saic 
Leaf- 
roll 
W—Green Mountain series: 
In root contact with Bliss Triumphs in 1922. 
20 
0 
0 
20 
‘6 
0 
73 
18 
0 
In root contact with mosaic Bliss Triumphs 
1922_ 
14 
0 
0 
14 
«5 
0 
51 
14 
0 
In root contact with leaf-roll Bliss Tri¬ 
umphs d in 1922_ 
2 
0 
0 
2 
1 
0 
8 
4 
0 
W—Bliss Triumph series _ 
20 
14 
d 2 
20 
14 
2 
100 
69 
8 
C—Green Mountain series: 
In root contact with Bliss Triumphs in 
1922. _____ 
17 
0 
0 
17 
• 1 
0 
65 
1 
0 
In root contact with mosaic Bliss Tri¬ 
umphs in 1922___ 
10 
0 
0 
10 
0 
0 
41 
0 
O' 
In root contact with leaf-roll Bliss Tri¬ 
umphs in 1922__ 
2 
0 
0 
2 
* 1 
0 
9 
1 
0 
C—Bliss Triumph series_ 
17 
10 
d 2 
17 
11 
2 
85 
54 
4 
W and C—Green Mountain series: 
In root contact with Bliss Triumphs in 
1922_ 
37 
0 
0 
37 
«7 
0 
138 
19 
0- 
In root contact with mosaic Bliss Tri¬ 
umphs in 1922_ 
24 
0 
0 
24 
'5 
0 
92 
14 
0 
In root contact with leaf-roll Bliss Tri¬ 
umphs in 1922_ 
4 
0 
0 
4 
c 2 
0 
17 
5 
O' 
W and C—Bliss Triumph series_ 
37 
24 
d 4 
37 
25 
4 
185 
123 
12: 
• Each from a hill of 1922. 
h Each hill grown from a different tuber (produced in 1922). 
c Including those partly diseased. 
d None of the leaf-roll Bliss Triumphs were also mosaic. 
• Partly diseased. 
15 Thrips are suspected as a carrier of a mosaic of Eucharis lilies. Whetzel, H. H. report of the; 
plant pathologist for the period January ist to may 3 ist, 1922. Bermuda Rpts. Bd. and Dept ^ 
Agr. 1922; 29, 30-31, 1923. 
