Sept. 15, 1925 
Cladosporium Leaf Mold of Tomato 
525 
region of advance of the stem-end blackening in the interior of three 
small green fruits, portions of the tissue were cut out with a flamed 
scalpel and planted in poured plates of 2 per cent dextrose potato 
agar. From 22 of the 24 plantings a similar Cladosporium developed 
which, in cultural and spore characters, closely resembled the leaf- 
mold fungus, Cladosporium fulvum Cke. While the destructive effects 
of this fungus were very evident on the foliage of this crop, it was not 
suspected until these isolations were made that it was the cause of the 
fruit rot. The fungus was also isolated from the leaves by plates 
poured from a spore suspension, and it seemed to be culturally identi¬ 
cal with the form isolated from the fruit. 
To prove the identity of the cultures isolated from the fruit, 
five young tomato plants were sprayed with a spore suspension 
1 >repared from one of the cultures, and in 15 days typical yellowed 
eaf lesions appeared which, 5 days later, showed sporulation. Later 
a second series of five plants was similarly inoculated with spores from 
a culture isolated from another fruit; and leaf lesions appeared in 17 
days, and sporulation 5. days later. The two series of control plants 
sprayed with water were not infected, and the disease was not ob¬ 
served to be present at anv time on other plants in the greenhouse. 
These results prove beyond question that it was the leaf-mold fungus 
in the blackened fruit tissues. Some of the tissue plantings had 
yielded bacteria as well as the fungus, indicating that the latter may 
be closely followed by secondary invaders in the diseased tissues. 
There was no sporulation of the fungus on the fruits, except in 
certain restricted locations, namely, about the margin of the torus 
scar, along radial epidermal cracks, and in the whitened papery spots 
already described (pi. 2, C). The sporophores were usually borne in 
dense tufts on rather conspicuous stromatic bodies, the black’dots 
in the fruit lesions previously mentioned. In the papery spots, 
these stromatic bodies had burst through the epidermis and were 
densely covered with sporophores (pi. 4, B), but in general these 
bodies did not break through the fruit epidermis. Agar plates were 
poured from the spores produced on the torus scar on an infected fruit, 
and the colonies were identical with isolations from a leaf and from 
the interior fruit tissue. 
Within the tissues of the fruit, the tendency of the fungus was to fill 
the intercellular spaces with composite strands of brown, thick-walled, 
f eniculate mycelium, with short, swollen cells (pi. 3, B, C; pi. 4, D, 
!). The individual hyphae become undulating or geniculate, each 
eventually bearing numerous short lateral knobs or projections which 
dovetail and interlock with those of adjacent hyphae to form a pseu- 
EXPLANATORY LEGEND FOR PLATE 3 
A. —Surface view of epidermis over a fruit lesion (such as that in PI. 1, E), showing the blackened 
subepidermal network produced, by the mycelium between the large parenchyma cells under the epi¬ 
dermis, and a few scattered sclerotial or stromatic bodies—the black dots visible to the unaided eye. 
Photomicrograph X 41. (All photomicrographs were made from unstained, free-hand sections of fresh 
material, unless otherwise stated) 
B. —Tangential section of pericarp just underneath epidermis, showing the dense intercellular aggregates 
of brown mycelium and the spherical, intercellular, sclerotial bodies. Photomicrograph X 94 
C—Section passing obliquely through a fibrovascular bundle in the pericarp tissue. Intercellular 
mycelium producing somewhat of a reticulum and forming denser aggregates between the parenchyma 
cells immediately surrounding the bundle,which is a characteristic behavior of the mycelium in the 
host tissues. Photomicrograph X 94 
D.—Calyx with one sepal (lower left) killed by early Cladosporium infection. The fruit was somewhat 
lopsided, the stunted side being under this sepal. Mycelium had penetrated into the fruit. Somewhat 
enlarged 
Library 
INVESTIGATIONS. 
