July i, x»i8 
True Nature of Spinach-Blight 
21 
The control plants in all of the cages were free from blight; therefore it 
was thought either that lettuce was an alternate host of the inciting 
factor of the disease or that in some unknown manner the plants became 
infected during the manipulation incidental to the transference of the 
aphids. 
In order to check these points, a duplication was made of the transfers 
of the Macrosiphum solanifolii from lettuce to spinach. In this series 
20 spinach plants were used, and io adult aphids born and reared on let¬ 
tuce were placed on each plant, as in the original series. Every precau¬ 
tion was taken to prevent the infection of the plants in any other man¬ 
ner than through the agency of the aphids. Twenty additional plants 
used as controls were untreated. Twenty plants were inoculated with 
the juice obtained by crushing the lettuce leaves from which the aphids 
had been taken. Four cases of blight developed in 22, 22, 29, and 36 
days, respectively, after inoculation among the plants upon which the 
aphids had been allowed to feed. All the untreated plants remained 
healthy, as did those which were prick-inoculated with the juice of lettuce 
leaves. Twenty control plants pricked with a flamed needle remained 
healthy. 
Twenty healthy spinach plants were inoculated with the juice of 
crushed Macrosiphum solanifolii taken from the original lettuce plants. 
Ten plants were pricked with a sterile needle and used as controls. Two 
of the inoculated plants developed positive symptoms of the disease in 
22 and 26 days, respectively. The 18 other plants in the series, together 
with the control plants, remained healthy until the experiment closed, 54 
days later. Another series of inoculations was made with the juices of 
aphids which had been feeding on lettuce, eggplant ( Solanum melongena ), 
and peppers (Capsicum spp.), to inoculate healthy spinach plants. 
In all cases M. solanifolii was used. The parent aphids were col¬ 
lected in the field from lettuce plants, brought to the greenhouse, and 
placed on the various food plants, on which they were allowed to remain 
until the first-generation offspring had been produced. The inoculations 
were made about the time the majority of the first generation had reached 
the fourth instar. The following results were obtained. 
Forty spinach plants inoculated with the juice of aphids collected 
from lettuce gave one positive infection, and the plant developed typical 
blight. Twenty plants were inoculated with the juice of aphids reared 
on eggplants; two positive infections resulted. Twenty plants inoculated 
with the juice of aphids reared on peppers remained healthy. Forty 
plants were pricked with a sterile needle and remained healthy. Three 
lots of 10 plants each were inoculated with the juice of crushed lettuce 
leaves, eggplant leaves, and pepper leaves. These plants remained 
healthy. 
