196 Journal of Agricultural Research voi. v, no. s 



Falls, N. Y.; Potomac Flats, Washington, D. C. ; Arlington, Va. ; etc. 

 It enters the stem end of the tubers most commonly, but also invades 

 lenticels and wounds. In some cases the affected tissue is light colored 

 and soft, suggesting bacterial rot — i. e., practically the jelly-end rot. 

 More often in the East it is characterized externally by a firm sunken 

 area with the underlying parenchyma brown to black, dry, tough, and 

 sharply differentiated from the healthy tissue. 



This stem-end wound and lenticel dry-rot caused by F. radicicola may 

 be regarded as a form of jelly-end rot. The organism is one of the causes 

 of jelly-end rot, but the field and storage conditions where it occurs are 

 different. Under conditions of high humidity the rot is of the jelly-end 

 type; where the humidity or temperature is low and the action of the 

 fungus less rapid, dry-rot develops, the affected tissue being more firm 

 and darker colored as a result of drying and oxidation. (See p. 197, 

 PI. XV, fig. 4, 5.) Both types occur in California, Oregon, and Idaho, 

 sections under irrigation. The dry-rot phase was the one most fre- 

 quently submitted for diagnosis from other localities — i. e., of presumably 

 slower development at lower temperatures. 



INOCULATION OP POTATO TUBERS WITH FUSARIUM RADICICOLA 



F. radicicola 2842; isolated in October, 191 3, from jelly-end rot of 

 Burbank potato from Middle River, Cal. Unfortunately, the number 

 of tubers in the experiment with this strain was not recorded. About 

 I peck of potatoes of the Burbank variety and K peck of the Netted Gem 

 variety were used for inoculation and controls. The tubers were incu- 

 bated at temperatures ranging from 14° to 20.3°; average lowest 

 compartment, 16.7°; highest, 18.2° C. After 37 days' iiicubation only 

 one tuber showed a rot; this was at an average temperature of 18.2° C. 

 The organism was recovered. 



The thirty-eighth day after inoculation the remaining tubers were 

 exposed to an average temperature of 22.8° C. for the succeeding 19 days. 

 At this time all inoculated tubers were rotted, all stages of wet-rot and 

 dry-rot being represented. The Netted Gems were more badly affected 

 than the Burbanks. In every case the organism was recovered where 

 the attempt was made, four reisolations being identified. 



F. radicicola 2890; isolated in October, 191 3, from a jelly-end rotted 

 tuber of the Burbank variety from Watsonville, Cal. (associated with 

 Rhizocionia sp. 2892). Culture used, 9-day-old pionnotes on a stem of 

 Melilotus alba. All inoculated tubers showed a progressive rot begin- 

 ning at the inoculation prick (PI. XVII) after 20 days' incubation at an 

 average temperature of 23° C. The lenticels were invaded and the 

 sprouts infected and dropping off. Some of the tubers were completely 

 softened, only a slimy mass remaining in the entire skin. The organism 

 was recovered by six reisolations. 



