Nov. II, 1918 Sweet-Poiato Storage-Rots 353 



Yam, Big Stem Jersey, Nancy Hall, Southern Queen, Dahomey, and 

 several varieties with accession numbers but not yet named. McClin- 

 tock (26) listed approximately these same varieties, stating that a 

 number of them had little or no scurf when grown for a season in Vir- 

 ginia. The writers have found, however, that many of the varieties he 

 listed as having little or no scurf were the most susceptible and worst 

 affected in other sections of the country. There is, in the opinion of the 

 writers, little difference in the susceptibility of the different varieties, 

 since varieties which have shown a degree of resistance in one section 

 of the country are not resistant in another. 



■ MINOR vSTORAGE-ROTS 



The following group of storage-rots are of minor importance. They 

 are caused by fungi occasionally met with and Vv^hich under the proper 

 environment will decay sweet potatoes. That they have not been more 

 frequently met may in part be due to the fact that they are slow-growing 

 forms, and as such may be crowded out or overrun by the more rapidly 

 growing saprophytes which follow them. This does not necessarily 

 presuppose the killing out of the casual fungus, although such might 

 well happen. It is a well-known fact that certain organisms do not live 

 long in their own staling products. Rhizopus nigricans, for instance, 

 will often die in two or three weeks in tissue previously destroyed by it. 

 Other organisms, saprophytes perhaps, may find abundant food there 

 and conditions otherwise congenial for their development. With 

 these facts in mind it is easy to understand why a saprophyte instead of 

 the causal fungus may be, and doubtless often is, isolated from decayed 

 tissue. Furthermore, the causal fungus and a saprophyte may both be 

 living congenially in the same decayed tissue, but when isolations are 

 made the latter, if the more rapid grower, which it usually is, will so 

 completely crowd out the parasite that only the saprophyte appears in 

 the plate. Likewise the temperatures at which sweet potatoes are 

 usually stored are the temperatures at which many of these minor rot- 

 producing organisms do not grow well. It is at the low or high tem- 

 perature, thus excluding some of the saprophytes, that some of these 

 fungi grow. These fungi therefore have been found to cause rots and 

 have been isolated from decayed potatoes held at a temperature lower 

 than that at which sweet potatoes are usually stored. 



With one or two exceptions none of the organisms have ever been 

 reported to have produced decay of sweet potatoes in storage. No 

 common names are known for these rots ; therefore they will be discussed 

 under the name of the causal organism. 

 83815°— 18 3 



