Soybean Mosaic 
95 
j 
an. i2,1924 
plot planted with seed from mosaic plants, 172 out of 993, or 17 per cent, 
of the seedlings were mosaic. Owing to the drought of 1922, the field 
symptoms were not easily recognizable at the time the seed was collected, 
and among 42 single plant selections from supposedly healthy plants, 
3 showed mosaic when tested. 
It would seem, therefore, that seed selection from mosaic-free plants 
may be fairly effective, but not absolutely infallible, as a control measure. 
SECONDARY SPREAD OF MOSAIC 
The degree of spread of mosaic during the season of 1921 is shown in 
Table I in which the number of mosaic plants on August 16 is very 
greatly in excess of those noted on June 26. In the Midwest variety 
this secondary infection involved 29 per cent of the stand. In another 
plot of the same variety, 37 per cent of the stand became infected during 
the month between July 19 and August 19. 
The spread of infection in 1922 was not so extensive as in 1921. In 
field plots, 14 per cent of the 2,174 Midwest plants, 16 per cent of the 
487 Haberlandt plants, and 1 per cent of the 640 Arlington plants became 
infected during the season. 
During 1923 the spread of infection was much more extensive than in 
the two preceding seasons. Among variety plots equally exposed to 
infection and showing no mosaic among the seedlings, the extent of 
secondary spread of mosaic is evidenced by the percentages of mosaic 
recorded August 7 to 14, as shown in Table V. The varieties Soysota 
and Virginia seemed to escape infection. 
Table V .—Secondary spread of mosaic , 1923 
Variety. 
Midwest... 
Manchu.... 
Haberlandt 
Elton. 
Feldun... . 
Dunfield... 
Wea. 
Arlington.. 
Ito San ... 
A. K. 
Number 
of plants. 
Per cent 
mosaic. 
Variety. 
Number 
of plants. 
Per cent 
mosaic. 
181 
90 
Brown. 
220 
41 
24 
79 
Lexington. 
92 
40 
76 
73 
Pinpu. 
50 
38 
28 
64 
Black Eyebrow. 
30 
33 
43 
63 
36847. 
30 
33 
38 
55 
Mammoth Yellow. 
79 
23 
60 
45 
Tar Heel Black. 
2 53 
22 
61 
44 
Wilson Black. 
329 
14 
211 
4 i 
Soysota... 
163 
2 
39 
4 i 
Virginia. 
308 
0.6 
The agent of dissemination has not been determined. Aphids have 
not been noted to any extent on the soybeans. Leafhoppers and 
tarnished plant bugs have been found in abundance, but numerous tests 
with caged plants have failed to incriminate either of these insects. 
EFFECT OF MOSAIC ON SEED GERMINATION 
Dickson (j, p. 18-19) has shown that there is a reduction in the ger¬ 
minating power of seed due to the mosaic disease in the case of red 
clover and Canada field pea, and Cunningham (2, p. 27) states that seed 
from mosaic bean plants has a low germinating quality. In the green¬ 
house tests with seed from mosaic soybean plants presented in Table 
II there was 79 per cent germination of the 676 Midwest seeds planted^ 
