Nov. II. i9i8 Sweet-Potato Storage-Rots 351 



The footrot fungus produces a relatively slow decay, two to three 

 weeks being required to destroy completely an average-sized potato. 

 It produces a somewhat spongy rot and turns the tissue brown. Upon 

 the escape of moisture it becomes dry, shrunken, hard, and finally brittle. 



CHARCOAL-ROT 



Charcoal-rot is a rather common type of storage-rot caused by Sclero- 

 tium hataticola Taub., and is distributed throughout the United States 

 and elsewhere. It has been collected widely, and specimens of sweet 

 potatoes have been received from Japan and other foreign countries de- 

 cayed by S. hataticola. The writers have often isolated it from the lower 

 part of the stem and underground parts of sweet-potato plants injured 

 in the field by other agencies. It will grow saprophytically on most any 

 substance, and occurs as a secondary invader both under field conditions 

 and in the stroage house. 



Sclerotium hataticola evidently was originally thought by Halsted {12) 

 to be a stage in the life history of Sphaeronema fimbriatum, but after a 

 more thorough study of the disease by Halsted and Fairchild (i^) it was 

 evident they entertained some doubt of its connection with the black- 

 rot fungus. Later investigations {34), however, showed that the sclero- 

 tial form was Sclerotium hataticola, and was in no way connected with 

 Sphaeronema fimbriatum. 



Sclerotium hataticola is another of the slow-growing storage-rot fungi, 

 requiring about 3 to 6 weeks to rot completely a potato under moist- 

 chamber conditions at laboratory temperature. The decayed tissue first 

 becomes a chocolate to a cinnamon-brown, followed by a dark reddish- 

 brown color. As soon as the sclerotia begin forming, it becomes black 

 or charcoal in appearance. Three distinct zones differing in color, there- 

 fore, may be distinguished in a potato at the same time. The black zone 

 contains the sclerotial bodies. Adjacent to this is a dark reddish-brown 

 area. The freshly decayed part is of a chocolate-brown color. 



The potato in the early stages of decay is spongy, but on the escape 

 of moisture it gradually becomes hard and mummified. In this stage 

 the epidermis is darkened from the action of the fungus, but there is 

 no other external indication that the potato is rotted. If the epidermis 

 is broken, the black sclerotial bodies may be seen in large numbers. In 

 a completely decayed potato these sclerotial bodies are buried among 

 the cells throughout the potato. 



INOCULATION EXPERIMENTS 



Several inoculation experiments were carried out at different times, 

 and in most cases when the well method described earlier was employed 

 positive results were obtained. The writers found that Sclerotium 

 hataticola, like some other storage-rot organisms, would not consistently 



