July i* 1918 
True Nature of Spinach-Blight 
13 
after inoculation the first blighted plants were observed. All of the 
control plants appeared healthy. Twenty-seven days after observing 
the first blighted plants a mottled leaf was removed from one of them, 
and with it seedling spinach plants in a pot in the greenhouse were in¬ 
oculated by mashing the diseased tissues into their leaves. A similar 
pot of seedlings was pricked with a flamed needle and served as a con¬ 
trol. Thirty-one days later three of the seedling plants had developed 
decidedly mottled leaves, typical of blight. All of the control plants 
appeared healthy. These results indicate that the original blighted 
plants contained a virus which, when extracted in water and inoculated 
into other field plants in the outdoor cages, produced a condition similar 
to the original blighted plants. Leaves from these artificially infected 
plants contained a virus which produced typical symptoms of blight in 
plants growing in the greenhouse, thus indicating that it is not unfavor¬ 
able soil nor temperature conditions which cause the disease in the field 
or in the greenhouse. 
DIRECT INOCULATIONS WITH THE JUICE OF BLIGHTED PLANTS IN WHICH 
THE DISEASE HAD BEEN PRODUCED BY APHIDS 
Blighted plants were collected from two large areas. Alate and ap, 
terous Macrosiphum solanifolii and Rhopalosiphum persicae were re¬ 
moved and placed on spinach seedlings in a field cage. Sixty-one days 
after transferring the aphids typical symptoms of blight appeared on 
two of the plants. Thirteen days later one more plant developed mot¬ 
tled leaves typical of blight. On the same day one mottled leaf was 
removed from each of the two blighted plants first observed in this 
cage, and was brought to the greenhouse for inoculation purposes. Ten 
spinach plants 49 days old were inoculated as follows: With a flamed 
needle, the juice from the mottled leaf of plant 1 was pricked into the 
healthy leaves of five seedlings in two pots, the other five seedlings in 
two pots being inoculated by mashing the blighted tissues into the 
leaves. Ten other spinach plants in four pots were inoculated in the 
same manner with a flamed needle and the mottled leaf from blighted 
plant 2. Two similar spinach plants in separate pots were pricked with 
a flamed needle to serve as controls. 
Twelve days after inoculation, one of the potted plants had developed 
the mottled leaves characteristic of blight; the other inoculated plants 
and the controls appeared healthy. Sixteen days after inoculation a 
photograph was taken to show the difference in appearance between 
the inoculated plants and a control (PI. 7, B). Twenty-four days after 
inoculation 13 of the 20 inoculated plants had developed mottled leaves 
characteristic of blight. The remaining inoculated plants, although not 
showing the mottled leaves, did not have the healthy appearance of the 
control plants. 
