May 29, 1916 



Fieldrot of Potato Tubers 



303 



Table II. — Summary and results of inoculating growing potato plants and tubers with 



Fusarium, radicicola 



Of the 30 Idaho Rural tubers sprayed, 15 showed infection with stem- 

 end and lenticel rot. Of the 30 Netted Gem tubers sprayed, 17 showed 

 stem-end rot. Lenticel rot did not occur on all of the Netted Gem 

 tubers and where it did occur the infections were very slight. The 

 thicker skin of the Netted Gem probably renders it more resistant to 

 fungus attacks than the Idaho Rural. The failure of a part of the 

 sprayed tubers to develop infection can probably be attributed to the 

 extremely dry condition of the soil. Infections resulting from spraying 

 the growing tubers with a suspension of the spores of F. radicicola 

 are shown in Plate XXXVI, figures i to 4. In figure 4, Plate XXXVI, is 

 shown an eye infection which has extended down into the vascular sys- 

 tem. F. radicicola was recovered from the discolored vascular tissue 

 of this tuber. None of the checks showed any infection. Twenty- 

 seven Idaho Rural tubers infected with stem-end rot resulted from the 

 puncturing of the 30 tuber stolons. The three which failed to develop 

 infection were under the same plant. Twenty-three of the Netted Gem 

 tubers whose stolons were inoculated showed stem-end infection. Seven 

 showed no evidence of infection in the tubers, though the stolons were 

 black and dead up to within about one-eighth of an inch of their juncture 

 with the tubers. Where infection in the tuber was found the line of 

 infection could easily be traced down the stolon from the point of inocu- 

 lation into the tuber. 



Tuber infections resulting from the inoculation of the stolons in the field 

 are shown in Plate XXXVII, figures 5 to 8. Both stem-end rot and vas- 

 cular infection are shown. Figure 8, Plate XXXVII, represents a Netted 

 Gem tuber with stem-end infection resulting from the inoculation of the 



