May 29, 1916 



Fieldrot of Potato Tubers 



301 



Fifty tubers each of Idaho Rural and Netted Gem, respectively, were 

 inoculated by methods i and 2, and twenty-five tubers each of Idaho Rural 

 and Netted Gem were inoculated by method 3. Checks on each experiment 

 were prepared in the same manner, except that in method i the tubers 

 were sprayed with sterile water, in method 2 the tubers were wounded 

 with a sterile needle, and in method 3 the broken stolon ends were 

 dipped in sterile water. Inoculated tubers and checks were placed in 

 moist chambers and put in the culture room of the Experiment Station 

 laboratory. During the course of these experiments the culture-room 

 temperature varied from a minimum of 20° to a maximum of 29° C. 

 Temperatures were taken daily at 8.30 a. m. and 5.30 p. m. After a 

 month the tubers were examined. Table I gives a summary of the 

 experiments and the number of tubers found infected. 



Table I. — Summary and results of laboratory inoculations of Solanum tuberosum 



Of the 50 Netted Gem tubers sprayed with the spore suspension, 48 

 showed infection. Stem-end infection was present in each of the inocu- 

 lated tubers. Lenticel infections were present on most of the tubers, 

 and eye infections were also found. Every Idaho Rural tuber sprayed 

 with the spore suspension showed infection at the stem end. The ma- 

 jority showed lenticel infections and several showed eye infections. Len- 

 ticel infections, induced by spraying with the spore suspension, are shown 

 in Plate XXXVI, figure 3. In figure 4 of Plate XXXVI is shown the 

 same tuber after remaining several days longer in the moist chamber. 

 Tufts of F. radicicola have appeared over the surface of the decayed areas. 



A stem-end infection of an Idaho Rural tuber sprayed with the spore 

 suspension is shown in Plate XXXVI, figure 5. Evejy tuber, whether 

 Netted Gem or Idaho Rural, developed infection when punctured at the 

 stem end with a needle carrying the spores of the fungus. Decays in- 

 duced in this manner are shown on Plate XXXVI, figures i and 2. 

 Twenty-five stem-end tuber infections resulted from the inoculation of 

 the broken stolon ends in the Netted Gems, and 19 in the Idaho Rurals. 

 The decay resulting from this method of inoculation was similar in every 



