Sept. 15, 1925 
Oladosporium Leaf Mold of Tomato 
539 
The mycelium is intercellular, and the fungus produces composite 
strands or pseudoparenchymatous aggregates which mummify the 
host tissues and form a reticulum in which the cavities represent 
the original host cells. The mycelium is not found within the 
fibrovascular bundles, but completely permeates the parenchyma 
and tends to accumulate most extensively between the parenchyma 
cells immediately adjacent to the vascular bundles. Invaded tissues 
may remain alive for a considerable period. 
Scattered throughout the affected tissues, the fungus forms, in 
the larger intercellular spaces, sclerotial or peritheciumlike bodies 
or bulbils 150 to 300 microns in diameter. No spores have been 
found within these bodies. Those formed under stomata in sepals, 
pedicel, and torus, and in certain restricted areas on the fruit lesions, 
may bear tufts of conidiophores. 
Mycelial growth and spore germination occur between 10° and 
30°, with an optimum at 20° to 25° C. 
In an infected fruit the fungus occurs in the pericarp, locule walls, 
and placentae, invariably, it would seem, in the torus, and frequently 
in one or more sepals and the last internode of the pedicel. 
No stomata have been found in the fruit. Histological studies 
and inoculation tests indicate that spore infection occurs rather 
early through stomata in the sepals, torus, or last pedicel internode, 
after which the mycelium grows down into the fruit, causing dark 
discoloration. The presence of infection in the sepals or torus may 
f iroduce a stunting effect on one side of the fruit which results in 
opsidedness of the fruit. Sepal infection is of common occurrence. 
The mycelium grows down through the placentae and invades 
the seeds both externally and internally. Sclerotial bodies are 
attached to the exterior of the hilum end of the seed coat. The 
fungus also grows into the parenchyma tissue of the middle layer 
of the seed coat at the hilum, penetrating as far as the endosperm, 
but not into the latter. Sclerotial bodies are formed within this 
middle-layer tissue. 
Fragments of infected fruit tissue may adhere to the seed coat 
of seeds extracted from diseased fruits. 
Under moist conditions the fungus sporulates on infected and 
contaminated seeds. Since the seed coat is often carried up on 
the cotyledons of the seedling, the spores may readily reach other 
seedlings. 
In germination, the cotyledons must emerge through the infected 
hilum region. Primary cotyledon infection occurred among seedlings 
grown in pots of sterile sand from both infected and surface-con¬ 
taminated seed which had been dried one month. 
LITERATURE CITED 
(1) Dickson, B. T. 
1920. stem-end rot of greenhouse tomatoes. Phytopathology 10: 
498-500, illus. 
(2) Fink, B. 
1894-98. pollination and reproduction of lycopersicum esculen- 
tum. Geol. and Nat. Hist. Survey Minn. Bui. (Bot. Ser. II) 
9: 636-643. 
(3) Fromme, F. D., and Thomas, H. E. 
1916. spraying and dusting tomatoes. Va. Agr. Exp. Sta. Bui. 213, 
14 p., illus. 
