Nov. 26, 1921 Susceptibility of Sweet Potatoes to Rhizopus 515 



SUMMARY 



(i) R. nigricans is parasitic on the following varieties of sweet potatoes : 

 Porto Rico, Big Stem Jersey, Triumph, Pierson, Gold Skin, Little Stem 

 Jersey, Georgia, Early Carolina, Nancy Hall, Florida, Red Brazil, Haiti, 

 Dahomey, Southern Queen, Yellow Belmont, and Dooley. R. tritici was 

 found to be parasitic on all the above-named varieties except Early Caro- 

 lina, Florida, Red Brazil, and Yellow Belmont, on which it was not tried. 



(2) With respect to their susceptibility to decay by these two species of 

 Rhizopus, the varieties can be separated roughly into three groups- — first, 

 those that are very susceptible ; second, those that are very resistant ; and, 

 third, those that are intermediate between the first and second. To the 

 first group belong the Gold Skin, Little Stem Jersey, Georgia, Early Caro- 

 hna. Red Brazil, Haiti, Yellow Belmont, and Dooley; to the second, 

 Southern Queen and Nancy Hall ; and to the third, Porto Rico, Big Stem 

 Jersey, Triumph, Pierson, Florida, and Dahomey. 



(3) Nancy Hall and Southern Queen, the two most resistant varieties, 

 were more susceptible to decay by R. tritici than by R. nigricans at a 

 temperature of from 20° to 22° C. Neither of these varieties, however, 

 deca5'-ed as readily as the Little Stem Jersey under similar conditions and 

 used as a control. 



(4) The results of these experiments show that all the varieties tried 

 (16) are more or less susceptible to decay by R. nigricans but that there 

 are some varietal differences. Likewise, the results show that those 

 varieties which decayed most readily under the conditions of these 

 experiments are the ones which have been observed to decay most readily 

 under commercial storage-house conditions. 



75308—22 5 



