May 29, 1916 



Fieldrot of Potato Tubers 



307 



end rot nor blackrot makes any progress in storage at a temperature of 

 48° or under. 



This conclusion is further substantiated by results obtained in storing 

 several sacks of blackrot-infected Idaho Rural and Pearl tubers for 

 experimental use in the fall of 191 3. Although the infected stock re- 

 mained in the cellar until the middle of May, 1914, when the cellar tem- 

 peratures had risen to something over 50° F., the tubers were apparently 

 as sound as at the time they were put in storage. Carpenter ^ has found 

 that when tubers were inoculated with F. radicicola and kept at a tem- 

 perature of 12° C. (approximately 53° F.) no rot developed. 



EFFECT OF PLANTING INFECTED SEED 



In the spring of 191 5 three plots were planted with infected seed 

 potatoes. Plot i was planted with Idaho Rural potatoes every 

 seed piece of which showed infection with F. radicicola, stem-end 

 blackrot, or lenticel rot. The presence of the fungus was verified by 

 artificial cultures. Plot 2 was planted with Pearl potatoes every seed 

 piece of which was infected with F. radicicola, stem-end blackrot, or 

 lenticel rot, the presence of the fungus being verified by artificial 

 cultures. Plot 3 was planted with Netted Gem potatoes infected 

 with jelly-end rot. The seed pieces were cut from the stem end, care 

 being exercised to see that at least one healthy eye was present on 

 each seed piece. Cultures from this seed gave a variety of fungi, 

 including F. radicicola and F. oxysporum. Check plots were planted 

 with the same varieties. The seed selected for the check plots was 

 entirely free from disease and was disinfected for i % hours in a solu- 

 tion of mercuric chlorid (4 ounces of mercuric chlorid to 30 gallons of 

 water). All of the plots were planted on alfalfa land which had never 

 before been planted to potatoes. The soil was a heavy clay loam of 

 lava-ash formation. Irrigation was given on July 4 and 5, July 16, 

 July 31, and August i. Throughout the season the plots were kept in 

 a good state of tilth, but they suff"ered somewhat from lack of moisture 

 during the latter part of August. Table III shows the percentage of 

 disease in the harvested product. 



Table III. — Percentage of disease in harvested potatoes 



> Carpenter, C. W. Op. cit. 



