Nov. II, 1918 Sweet-Potato Storage-Rots 365 



vStTMMARY 



(i) Storage- rots of sweet potatoes are estimated to cause a loss of 

 many million dollars annually. 



(2) Seventeen different fvmgi were found responsible for the decay of 

 sweet potatoes in storage. 



(3) A few of these fungi — viz, Rhizopus nigricans, Sphaeronema 

 fimbriatum, Diplodia tuber icola, Diaporthe batatatis, Plenodomus destruens, 

 Sclerotium bataticola, and Monilochaetes infuscans are responsible for 

 the most of the loss. 



(4) The following fungi cause losses in storage under favorable condi- 

 tions and are designated as the minor rot-producing fungi: Mucor 

 racemosus, Alternaria sp., Penicillium sp., Botrytis cinerea, Epicoccum 

 sp., Gibberella saubinetii, Fusarium culmorum, F. acuminatum, and 

 Trichoderma koningi. 



(5) Most of these fungi are weak wound parasites capable of causing 

 decay of sweet potatoes only under particularly favorable conditions. 

 Rhizopus nigricans, which probably causes more loss than any other 

 organism, would not consistently infect sweet potatoes without first 

 germinating the spores. When the germinated spores and decoction in 

 which they were suspended were poured into a "well" in the potato, 

 infection would usually follow. 



(6) After infection had once started, Rhizopus nigricans would com- 

 plete the destruction of a potato in an atmosphere almost entirely lacking 

 moisture. 



(7) There was great variation in the time required for the different 

 fungi to completely decay a potato. For Rhizopus nigricans from three 

 to five days were required. Diplodia tubericola, Diaporthe batatatis, and 

 others required three to eight weeks under similar conditions. 



(8) Most of the fungi required a considerable amount of moisture. 

 In fact, wrapping in moistened filter paper was often necessary after 

 inoculation by the "well" method. Diplodia tubericola, on the other 

 hand, grows as well or better in a humidity of about that of the laboratory 

 room. 



(9) The optimum temperature" of the different organisms varied con- 

 siderably. The optimum for Rhizopus nigricans was comparatively 

 high, but it would decay the potatoes over a considerable range of tem- 

 peratures. On the other hand, Mucor racemosus, Fusarium culmorum, 

 F. acuminatum, and others had a relatively low optimum. 



(10) Some of these storage-rot fungi are also the cause of field diseases 

 of sweet potatoes. Such are Sphaeronema fimbriatum, Plenodomus 

 destruens, and Monilochaetes infuscans. 



