juiyio,i 9 i6 Storage-Rots of Economic Avoids 567 



dasheens and sweet potatoes continue to absorb water for some time, 

 and sweet potatoes will take up as much as 7 to 20 per cent of their weight 

 in 24 hours, depending naturally on how dry they were when immersed. 

 Relatively the greatest absorption takes place during the first two hours ; 

 in extreme cases as much as 10 per cent. The rate of absorption drops 

 off at the end of that time, but the curve continues steadily upward 

 thereafter. 



Sclerotium rolfsii also requires considerable moisture to start growth, 

 but requires no addition of water to that in the filter paper of a moist 

 chamber after 24 hours. This fungus may have the power after once 

 becoming well established to penetrate the corky layer over a cut surface. 

 Whether this is accomplished by the action of an enzym was not 

 determined. 



Diplodia tubericola and the other closely related forms used in these 

 experiments succeed better under exactly the opposite conditions. If 

 the tubers after inoculation were subjected to the environment of the 

 laboratory room, the results were better than if they were kept in a moist 

 chamber. No attempt has been made to determine a cause for this 

 phenomenon. It must be kept in mind that at the outset protection was 

 afforded the spores and hyphas by inserting them about a fourth of an 

 inch into the tuber and the tissue squeezed together about the wound. 



Bacillus carotovorus, like S. rolfsii and F. solani succeeded better if a 

 film of moisture was sprayed on the cut surface for a day or two following 

 inoculation. As soon, however, as decay set in, no further application was 

 required, except to the filter paper in the bottom of the moist chamber. 

 It should be noted in this connection also that dasheens, turnips, and 

 carrots differ very much in respect to the moisture actually required to 

 stimulate decay. Dasheens are very dry and absorb moisture quickly 

 and must be sprayed several times to start decay. Turnips and carrots, 

 on the other hand, require but little added moisture, decay starting more 

 promptly and progressing more rapidly. 



TEMPERATURE AS A FACTOR IN PRODUCING ROT 



Temperature and moisture, so far as their relation to storage rots are 

 concerned, are so closely associated that one can hardly be discussed 

 independently of the other. 



It is obvious that decay will not occur at a temperature at which the 

 organism will not grow even in the presence of sufficient moisture or in the 

 absence of moisture with the proper temperature. 



Results with Diplodia tubericola. — A number of dasheens inocu- 

 lated with Diplodia tubericola from sweet potatoes were divided into two 

 lots, one of which was placed in an incubator with a temperature vary- 

 ing from 34 to 35 ° C. The other lot was placed in an ice box with a 

 temperature ranging from 12. 2 to 13. 5 . At the higher temperature 



