^oo Journal of Agricultural Research voi. vi, N0.9 



In the irrigated portions of Idaho the economic importance of the dis- 

 ease has varied greatly from year to year. In 191 3 the writer was usually 

 able to find only an occasional rotted tuber in any one commercial field. 

 In a few fields which had been planted on raw desert land and poorly 

 cared for he found as high as 80 per cent of the tubers infected with stem- 

 end blackrot and lenticel rot. The year 1914 might be called an epidemic 

 year. In one 50-acre field of Netted Gems near Jerome, Idaho, he found 

 as high as 40 per cent of the crop infected with jelly-end rot. Similar 

 conditions were observed in many other fields in the irrigated portions of 

 southern Idaho. Stem-end blackrot and lenticel rot were also found 

 very abundant in the fields of Idaho Rurals. It is significant that in 191 4 

 a freeze occurred in June which killed the vines to the ground, the plants 

 coming up anew and producing a crop. Often the origin of infection 

 could be traced from the frozen tip of the vine down through the stem 

 to the infected tubers. Although infected tubers were found in most of 

 the commercial fields visited in 191 5, the disease this year was of slight 



importance. 



EXPERIMENTAL WORK 



PREUMINARY EXPERIMENT IN I914 



In the fall of 191 4 ten Idaho Rural tubers and ten Netted Gem tubers 

 were disinfected by dipping in formaldehyde and were punctured at the 

 stem end with a needle carrying spores from a culture of F. radicicola which 

 had been isolated from a potato tuber infected with blackrot. After 

 inoculation the tubers were placed in moist chambers, where they re- 

 mained for something over a month. An examination of the tubers 

 showed that infection had been produced in every tuber inoculated. The 

 infection in the Idaho Rurals was similar in all respects to the blackrot 

 occurring in the field. The infection in the Netted Gems was not quite 

 so dark in color as that produced in the Idaho Rurals and resembled 

 certain stages of jelly-end rot collected in the field. No checks were 

 prepared. 



LABORATORY EXPERIMENTS IN I915 



On August 6, young and apparently healthy potato tubers of the 

 Netted Gem and Idaho Rural varieties were selected, carefully washed, 

 and disinfected in a solution of formaldehyde (i : 240). After disinfec- 

 tion the tubers were dried and inoculated with F. radicicola. The 

 methods of inoculation were as follows: (i) By spraying with a spore 

 suspension; (2) by wounding the tubers with a needle bearing spores; 

 and (3) by dipping the broken stolon ends in a spore suspension. In 

 method 3 the tubers were taken from the field with their stolons at- 

 tached. After disinfection each stolon was broken off afresh at from i 

 to 2 inches from its junction with the tuber and inoculated as stated in 

 the foregoing. 



