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Journal of Agricultural Research 
Vol. XXI, No. 9 
a weft of fine, white mycelium and numerous small spherical sclerotia 
could be seen (PI. 126). Sclerotia were noted also in the sheath tissues. 
Apparently the sheath is the first part of the plant to be attacked. 
Indications are that the sclerotia float on the water and thus come 
in contact with the leaf sheath, where they germinate and penetrate the 
tissues, causing dark brown areas. These lower sheaths die when sub¬ 
merged in the irrigation water, and the fungus lives more or less as a 
saprophyte in the dead tissues and finally attacks the stems after the 
plants are older. The most severe damage is caused at the time the 
vitality of the stem is declining and the panicles are filling. The plants 
are weakened, and the resulting panicles are poorly filled and light. 
The fungus is easily cultured from sclerotia by dipping them in alcohol 
and then in mercuric chlorid (1 to 1,000) for five minutes, washing in 
sterile water, and plating on agar. Fragment cultures from invaded 
tissues also are successful. The organism grows vigorously on boiled 
rice and produces an abundance of the small black sclerotia. The 
mycelium, which is normally white, becomes a dark smoky color at the 
surface of the medium. The hyphae are 3 to 5 microns in diameter, 
septate, and profusely branched. Dry, mature sclerotia from the dis¬ 
eased stems range in size from 220 to 270 microns in diameter, averag¬ 
ing about 250 microns. They are black, and rather uniformly spherical, 
with a smooth surface. 
Cattaneo 1 described the organism in Italy in 1879 as follows: 
Sclerotia black, 1/10 mm. in diameter, glistening, arising from a slendor white 
mycelium. 
The measurements of sclerotia given by Cattaneo are smaller than 
sclerotial measurements of the form found in Louisiana, but in all prob¬ 
ability his measurements were roughly made. Shaw 2 3 gives a range of 
measurements of the sclerotia of Sclerotium oryzae which easily covers 
the dimensions of the American form. Shaw measured sclerotia from 
cultures, however, and this probably accounts for the wider variation in 
size. His description of the fungus on glucose agar is as follows: 
The sclerotia are at first visible as minute circular spots of a grayish color; sub¬ 
sequently they become black and shiny, exactly resembling those found in the rice 
plant. The hyphae are of the usual type, the cells being about 4 to 6 microns broad 
and 150 to 350 microns long. They contain numerous oil globules and frequently 
branch. A tranverse septum occurs at the point of origin of a branch and not some 
distance from it. The sclerotia are roughly circular and vary in diameter from 150 to 
500 microns. They arise from a plexus of interlacing hyphae which continue to branch 
and intertwine until a small, spherical mass is formed. For a time the young sclero¬ 
tium increases in size by the adhesion of fresh branches to the periphery; ultimately 
the cell walls turn black and all further growth ceases. 
Symptoms of the disease given by the eastern writers are identical with 
the symptoms of diseased plants in Louisiana with the exception of tiller- 
1 Cattaneo, Achille. sullo sclerotium oryzae, nuovo parassita vEGETalE . . . In Arch. Lab. 
Bot Crittogamico R. Univ. Pavia, v. 2/3, p. 75-83, pi. 7. 1879. Bibliografia del genere Sclerotium, p. 81-83. 
3 Shaw, F. J. F. a sclerotial disease op rice. In India Dept Agr. Mem. Bot. ser., v. 6, no. 2, p. 11-23, 
3 pi. 1913. Bibliography, p. 21-22. 
