560 Journal of Agricultural Research vol. vi, No. 15 



CAUSE OE SCLEROTIUM-ROT 



The sclerotium-rot is caused by Sclerotium roljsii Sacc., a fungus 

 which was first mentioned by Rolfs (6, p. 31) in 1893 and technically 

 described by Saccardo (7, p. 257) in 191 1. 



In about seven days after inoculation in a moist chamber the sclerotial 

 bodies begin forming. They are almost spherical, at first white, but 

 later becoming brown, and finally nearly black, with a hard, shiny 

 surface. This organism, the sclerotial bodies of which are composed 

 of solid masses of fungus tissue, is, according to Wolf (10), parasitic on 

 peanuts and a number of other legumes. 



INOCULATION EXPERIMENTS 



All inoculations were made in moist chambers and kept in the labora- 

 tory except those in which temperature relations were studied, the 

 results of which are discussed later. All attempts to produce the rot by 

 placing bits of hyphae on an unbroken surface of the tuber were unsuc- 

 cessful. It was later found, however, that when the inoculations were 

 made on a cut surface or in a small wound made by a scalpel they were 

 uniformly successful if sufficient moisture was provided at the outset. 

 Moisture was consequently furnished by spraying once or twice with 

 water from an atomizer, and after 24 to 48 hours further applications 

 of water were unnecessary. The fungus grows very rapidly and in a 

 few days covers the whole surface of a tuber (PI. LXXXII, fig. 3) split 

 in two and even spreads onto the unwounded surface, although the scales 

 of these aroids appear to be impenetrable by the fungus. Within a week 

 the tissue is softened for half an inch or more, although under favorable 

 conditions a month is often required to decay completely a tuber. 



INOCULATION OF COLOCASIA ESCULENTA 



On January 14, 191 5, six tubers of the Trinidad dasheen were inocu- 

 lated with 5. roljsii by placing bits of hyphse on a cut surface. Decay 

 started in 2 days, and in 13 days the hyphae had overrun the whole cut 

 surface of the tuber and softened the tissue to the depth of half an inch. 

 The checks, six in number, remained sound. On January 27 six tubers 

 were inoculated, and by February 9 the tubers were well rotted and 

 sclerotia forming. The checks, four in number, remained sound. On 

 February 2 sixteen tubers were inoculated', and in 13 days all were 

 softrotted and covered with a dense growth of hyphae. The checks, five 

 in all, remained sound. On February 6 four tubers were inoculated on 

 an unbroken surface, but no growth had taken place by February 23, 

 and they were thrown out. No checks. On February 15 eight tubers 

 were inoculated and in 8 days they were all soft rotted, with sclerotia 

 developing abundantly. Two tubers were inoculated on March 6 at the 

 end in a small wound made by a scalpel and were well rotted by March 1 5 . 



