Aug. 21, 1916 Control of Powdery Dryrot of Potatoes 819 



PARASITISM OF FUSARIUM TRICHOTHECIOIDES 



To determine the parasitism of F. trichoihecioides , several attempts 

 were made to induce infection in various parts of growing plants and in 

 mature tubers. 



1. In the fall of 191 3 half -bushel lots of unbruised tubers were obtained 

 of each of the following varieties: Burbank, Idaho Rural, Early Rose, 

 Peoples, Improved Peachblow, Netted Gem, and Pearl. All of the 

 tubers selected were free from any external evidence of disease and were 

 disinfected by dipping in a solution of formaldehyde (1 1240). Each tuber 

 in one half -bushel lot of each variety was bruised with a sterile knife and 

 the bruised surface dipped in a suspension of the spores of the fungus. 

 Each tuber in another half-bushel lot of each variety was first carefully 

 examined to make sure that its skin was wholly sound and was then 

 dipped in a suspension of the spores of the fungus. Checks of the same 

 quantity of tubers of each variety were prepared in the same manner, 

 except that the tubers, whether sound or bruised, were dipped in sterile 

 water. Each lot was then placed in a sterilized canvas sack. To insure 

 a high degree of humidity each sack was sprayed with sterile water. The 

 sacks were then stored in one corner of the cellar and covered with canvas. 

 The tubers were not examined until the following May, or about seven 

 months after having been placed in storage. At the time of examination 

 all tubers had sprouted, showing that temperature conditions, at least 

 during the latter part of the storage period, had been ideal for the 

 development of the rot. Every inoculated, bruised tuber showed infec- 

 tion, each bruised, inoculated tuber being from one-eighth to three- 

 fourths decayed. None of the inoculated sound tubers showed any 

 infection. In the checks there was a slight amount of decay in many of 

 the bruised tubers, though they had not been inoculated; but all of the 

 sound tubers of the checks remained sound throughout the storage 

 period. 



2. In the fall of 1914 further attempts were made to infect potato 

 tubers with F. trichoihecioides through the unbroken skin. The following 

 varieties were employed: Improved Peachblow, Idaho Rural, Netted 

 Gem, Peoples, and Pearl. Fifty sound tubers of each variety were first 

 disinfected in a formaldehyde solution (1:240), dried, and then dipped 

 in a spore suspension of the fungus. Fifty tubers of each variety were 

 disinfected in the same manner, bruised with a sterile knife, and dipped 

 in a suspension of the spores of the fungus. Each lot of tubers was then 

 placed in a disinfected canvas sack. The potatoes were first stored in 

 the laboratory culture room, where the temperature was very favorable 

 to the development of the decay. A high humidity was maintained 

 in the culture room by spraying the walls with sterile water. After a 

 month the potatoes were removed from the culture room to the potato 

 storage cellar, where they remained until spring. An examination of 



