464 
Journal of Agricultural Research 
Vol. XXX, No. 5 
was almost dusty and only about 10 
per cent of the windfalls showed the 
disease. 
On October 29, 1923, the junior 
writer assisted in the inspection of a 
car of Delicious apples at Chicago, 
shipped from Wenatchee, Wash. Many 
of the apples were incrusted with clay, 
and one of them showed the character¬ 
istic symptoms of Phytophthora rot. 
A pure culture of Phytophthora was 
obtained from this apple. On January 
11, 1924, the rot was found in Rome 
Beauty apples from Boise, Idaho, in¬ 
spected in cold storage at Chicago. 
Plantings from affected fruits yielded 
only Phytophthora. 
DESCRIPTION OF THE DISEASE 
A brief description of Phytophthora 
rot on pears has been given in the first 
paragraph of this paper. However, 
there are certain characteristics of the 
rot on both pears and apples which 
merit further consideration, since a 
search of the literature shows them not to 
have been described in any detail before. 
Throughout the following discussion, 
which is based on a study of naturally in¬ 
fected fruits and of fruits inoculated in 
the laboratory, it is to be understood 
that all statements refer to tissues 
affected by the fungus. In both pears 
and apples there is always a marked 
vascular browning, both in the larger 
bundles near the core and in the smaller 
ones throughout the flesh (pi. 1, B and 
D). Very often the browning in the 
larger bundles extends to the stem and 
into it for part or all of its length (pi. 
1, B) in the manner described by 
Schoevers (12, p. 154 ). 2 In this con¬ 
nection it may be mentioned also that 
Rose (10) found marked vascular 
browning in strawberries parasitized by 
a fungus very similar to and apparently 
identical with ' Phytophthora cactorum. 
In apples the flesh surrounding the 
bundles is lightly browned, in pears 
scarcely at all. In some varieties of 
pears, notably Clairgeau, the flesh is in 
Tact decolorized and has a clear, water- 
soaked appearance very much like that 
of apple flesh affected by water-core. 
The parasitized flesh of both apples 
and pears sometimes becomes slightly 
spongy, but is usually as firm as sound 
healthy flesh; it rarely becomes soft 
and mushy like that found in lesions 
produced by Rhizopus or Penicillium. 
The only exception noted was that of 
pears of the Seckel variety, inoculated 
with Phytophthora in the laboratory. 
In cross-section, Phytophthora lesions 
on both pears and apples show indefi¬ 
nite boundaries so that it is impossible 
to make a clean separation of diseased 
from healthy flesh, as can so easily be 
done in fruits attacked by Rhizopus or 
Penicillium. The affected flesh has no 
marked odor or taste. Externally the 
lesions produced by Phytophthora on 
apples are light brown (pi. 1, C), on 
pears dark brown to black (pi. 1, A). 
INOCULATION EXPERIMENTS 
EXPERIMENT 1 
Twelve Clairgeau pears were washed 
in soap and water and rinsed in ster¬ 
ilized tap water. They were then ster¬ 
ilized for 10 minutes in 1: 1,000 mer¬ 
curic chloride solution, rinsed again in 
sterilized tap water, and placed in two 
moist chambers. Six were inoculated 
with a pure culture of Phytophthora 
obtained from Clairgeau pears and six 
were used as controls. 
On the fourth day all the inoculated 
pears showed the characteristic lesions, 
and all the controls were free from any 
symptoms of the disease. The lesions 
ranged in size from 33 to 44 mm. in 
superficial diameter, averaging 37 mm. 
On the tenth day the controls were still 
in perfect condition, while the lesions 
on the inoculated fruits varied from 70 
to 77 mm. in superficial diameter, aver¬ 
aging 74 mm. Cultures from these 
lesions yielded only Phytophthora. 
EXPERIMENT 2 
Eighteen apparently uninjured Kief- 
fer pears were sterilized in 1: 1,000 
mercuric chloride for 10 minutes. Six 
used for controls were placed in a moist 
chamber with water in the bottom. 
A layer of cotton batting was placed 
in the bottom of a moist chamber and 
saturated with sterile water. On the 
cotton batting were placed six small 
pieces of an agar culture of the Phy¬ 
tophthora which had been isolated from 
Clairgeau pears. A sterilized pear was 
placed on each piece of agar culture. 
On the eighth day three of the pears, 
and on the thirteenth day all of them, 
2 Reference is made by numbers (italic) to “ Literature cited,” p. 468. 
EXPLANATORY LEGEND FOR PLATE 1 
A. —Anjou pear five days after inoculation with the Phytophthora isolated from a naturally infected pear 
B. —Cross-section of the pear shown in A 
C. —Grimes Golden apple five days after inoculation with the Phytophthora isolated from a naturally 
infected pear 
D. —Cross-section of the apple shown in A (Color plate by J. Marion ShulP 
