SCLEROTINIA CARUNCULOIDES, THE CAUSE OF A 
SERIOUS DISEASE OF THE MULBERRY (MORUS ALBA ) 1 
By Eugene A. SiEGLER, Assistant Pathologist , Office of Fruit-Disease Investigations 
and Anna E. Jenkins, Assistant Mycologist , Office of Pathological Collections, 
Bureau of Plant Industry, United States Department of Agriculture 
In 1903, Orton 2 described a disease of the mulberry characterized by 
the “peculiarly enlarged portions of the aggregated fruit.'’ The disease 
was said to occur in Georgia, Alabama, and Mississippi. Dr. M. B. Waite, 
Pathologist in Charge, Office of Fruit Disease Investigations, Bureau of 
Plant Industry, states that specimens of mulberry fruits showing this 
condition have been received from various southern States by the United 
States Department of Agriculture a number of times during the past 20 
years. Taubenhaus 3 reports the occurrence of this disease in Texas, 
where it is known under the name of “popcorn” disease of mulberry. 
In July, 1920, specimens of diseased mulberry fruits (Morns alba L.) 
were received from Scranton, S. C. Specimens of this material show the 
greatly enlarged condition of the ovary (PI. 1, A), and the calyx lobes are 
small and nonsucculent instead of being fleshy as in the normal fruits. 
Upon microscopical examination the ovaries are found to be entirely filled 
with mycelium and all traces of- host tissue are lost. The hyphae 
are compact, producing a typical sclerotium, and preventing the 
formation or further development of drupelets. A layer of sporogenous 
hyphae completely envelops this sclerotium and produces small hyaline 
spores in a compact palisade within the ovary wall (PI. 1, B). The spores, 
presumably microconidia, are often exuded in immense numbers and 
collect in what resembles a waxy mass on the outside of the ovary 
wall (PI. 1, C, a). It is interesting to note the occurrence of microconidia 
on the diseased fruit, as no reference to microconidia of species of Sclero- 
tinia occurring other than on culture media has been found in the liter¬ 
ature. This disease undoubtedly is the same as that reported by Orton. 4 
The nature of the disease led us to suspect that we had either a species 
of Sphacelia, or, more probably, the microconidial stage of the genus 
Sclerotinia. It was thought that infection probably occurred at the 
blooming period of the host and resulted in the formation of such a sclero¬ 
tium. Accordingly on March 18, 1921, an inspection was made of the 
planting in South Carolina from which diseased specimens had been re¬ 
ceived in 1920. At that time apothecia (PI. 2, A) of a fungus belonging 
to the genus Sclerotinia were found in large numbers on the ground 
beneath the infected trees. The apothecia were attached to the infected 
1 Accepted for publication Oct. 28,1921. The technical description from page 83 5 of this paper was printed 
in Science, vol. 55, no. 1422, p. 353, March 31, 1922. 
2 Orton, W. A. on a fungus disease of the mulberry fruit. (Abstract.) In Exp. Sta. Rec., v. 14, 
no. 6, p. 531-532. 1903. 
3 Taubenhaus, J. J. on a peculiar disease of mulberry fruit. In Nature Study Rev., v. 17, no. 7, 
p. 282-285, 3 fig. 1921. 
4 Orton, W. A. op. cit. 
Journal of Agricultural Research, 
Washington, D. C. 
abv 
(833) 
Vol. XXIII, No. 10 
Mar. io, 1923 
Key No. G 287 
