July i, 1918 
True Nature of Spinach-Blight 
15 
similar pot of seedlings was pricked with a flamed needle and served as 
a control. Seven days after inoculation the two pots, of two and four 
plants, respectively, developed typical symptoms of blight. Nine days 
after inoculation the six plants in one pot developed doubtful symptoms 
and five days later all of these plants had developed positive symptoms 
of blight. Twenty-one days after inoculation all of the above plants 
were in advanced stages of blight, while the control plants remained 
healthy. These results indicate that the aphids from the original blighted 
field plants served as carriers of the virus, because the plants which 
blighted as a result of the feeding of the aphids on them contained a 
virus which produced the disease when pricked into healthy spinach 
plants. 
INOCULATIONS WITH THE TISSUES OR BLIGHTED PLANTS IN WHICH THE 
DISEASE WAS PRODUCED BY APHIDS 
A number of Rhopalosiphum persicae and Macrosiphum solanifolii were 
removed from blighted plants and placed on a pot of seedling spinach 
13 days old. This pot contained more than 100 seedlings. A similar 
pot of seedlings served as a control. Eighteen days after inoculation a 
few plants in the above pot had developed typical symptoms of blight. 
Thirty-four days after inoculation the majority of the inoculated plants 
had developed symptoms of the disease, while the control plants still 
appeared healthy. The majority of the inoculated plants eventually 
became much stunted and many died, but the control plants remained 
healthy (PI. 8, A). 
Eighteen days after inoculation two of the blighted plants were removed 
from the above pot and two seedling spinach plants were inoculated with 
them by pricking through the mottled leaves into the leaves of the seed¬ 
lings with a flamed needle. A third plant in another pot was pricked 
with a flamed needle to serve as a control. These pots of plants were 
placed in a cage in the greenhouse. With the two blighted plants used 
for the greenhouse inoculations six plants in a field cage were inoculated 
by pricking through the blighted leaves into the leaves of the healthy 
plants. Seventy-nine days after inoculation four of the six caged field 
plants showed positive symptoms of spinach blight. Fourteen days after 
inoculation the two seedlings in the pot in the greenhouse had developed 
mottled leaves, while the control remained healthy. Eighty-four days 
after inoculation a photograph was taken to show the appearance of the 
control as compared with the inoculated plants (PI. 8, B). These results 
indicate that spinach-blight is due to a specific virus which is readily 
transmitted from the field to the greenhouse, and vice versa, either by 
means of aphids which have fed on diseased plants or by transferring the 
juice of the diseased plants by needle pricks. 
