THE FUNGUS CAUSING THE COMMON BROWN ROT OF 
FRUITS IN AMERICA 1 
By John W. Roberts, Pathologist , and John C. Dunegan, Junior Pathologist , 
Fruit Disease Investigations, Bureau of Plant Industry, United States Depart* 
ment of Agriculture 
Since investigators of the fungus causing the disease of fruits in the United 
States commonly referred to as “brown rot” have bestowed upon it several 
specific names, it seems worth while to determine, if possible, which name should 
be retained as the correct one. For many years the scientific name was gen¬ 
erally accepted as Oidium fructigenum and later as Monilia fructigena, the Amer¬ 
ican fungus being considered identical with the supposed single form of Europe, 
then passing under these names. As early as 1893 Schroter (11, p. 67) 2 by 
analogy had referred Monilia fructigena to the genus Sclerotinia, though he had 
not found an ascogenous stage and had no knowledge of its existence. Woronin 
(15) in 1900 showed that Sclerotinia fructigena is different from S. cinerea , the 
conidial stage of which was described by Bonorden (2, p. 76) in 1851 as Monilia 
cinerea and also referred to the genus Sclerotinia by Schroter (11, p. 67) in 1893. 
Since Woronin’s conclusions were not immediately accepted, most investigators 
continued to use the name Monilia fructigena for the so-called brown rot fungus. 
After Norton (7) in 1902 proved that the species of Monilia causing the common 
brown rot of the peach in the United States is a conidial stage of a species of 
Sclerotinia, the name Sclerotinia fructigena came into general use. Later when 
Aderhold and Ruhland (1), Matheny (6), Conel (8), and other workers showed 
that the form common in America is not Sclerotinia fructigena but closely re¬ 
sembles and probably is identical with S. cinerea, the latter name became the 
one commonly accepted. Wormald (18), while studying the American and 
European forms, found that there were races or strains in S. cinerea. The 
American form being different from any of his European strains, he named it 
Sclerotinia cinerea forma americana. 
Wormald (18) working with 13 strains of the American form found them to 
fruit more readily than the strains occuring in Britain and to show other slight 
differences when grown on artificial culture media. A constant but slight mor¬ 
phological difference was found in the conidial germ tubes. In the American 
strains these are at least 200 microns long before branching begins, while in the 
strains from Britain the germ tubes branch when quite short and are usually 
geniculate'at one or more points. Wormald (14), has also recently described 
an ascogenous stage occurring in Britain that appears to be identical with ours, 
as indicated by his table showing measurements of asci and spores of both forms. * 
In the same publication he states: 
It seems certain, therefore, that the earlier records of the Sclerotinia in America were not of S. fructigena 
(Pers.) Schroter, and the more recent records show that the American form is one of which the conidial 
fructifications are indistinguishable from those of Monilia cinerea Bon. Of 13 strains of Monilia obtained 
by the present writer from various sources in North America, each has proved to be a fungus with a Monilia 
stage very similar to the gray Monilia common in Britain, but differing from the latter in its more copious 
1 Received for publication June 21,1924—issued Nov., 1924. 
* Reference is made by number (italic) to u Literature cited" p. 959-960. 
Journal of Agricultural Research, 
Washington, D. C. 
( 955 ) 
Vol. XXVIII, No. 9 
May 31,1924 
Key No. G-408 
