July 24, 1910 



Disease of Potatoes Known as "Leak " 



633 



In the inoculation experiments 210 sound potatoes of the Burbank 

 variety were used, of which 177, or 84 per cent, were rotted. 



Besides .the experiments with California-grown potatoes, inoculation 

 experiments were carried out with several eastern-grown varieties. These 

 potatoes were kindly furnished by the Office of Horticulture and Pomo- 

 logical Investigations in most cases. The tubers were inoculated in deep 

 wounds inclosed with a ring and cover glass, according to the method 

 already described. Five different isolations of the fungus were used with 

 each variety of potatoes. After inoculation they were placed in an incu- 

 bator maintained at 30 C. and left there throughout the experiment. 

 The results of this experiment are shown in Table I. 



Table I. — Results of inoculating several varieties of eastern-grown potatoes with Pythium 

 debaryanum, as shown by the number of potatoes of each variety rotted 



1 Furnished by Mr. W. B. Clark, of the Office of Cotton and Truck Disease Investigations. 



From the results shown in Table I it is evident that some of the varie- 

 ties of eastern potatoes are about as susceptible to this disease as Cali- 

 fornia-grown Burbanks used in the experiments already desciibed. 

 Early Ohio was apparently most susceptible, in that 10 potatoes rotted 

 out of 1 1 inoculated. The other varieties seemed somewhat more 

 resistant to this disease. 



Inoculations were also made, using potatoes of undetermined varieties 

 purchased in the Washington markets. A fair percentage of these inocu- 

 lations were successful in all cases. It would seem, then, that suscepti- 

 bility to this disease is not necessarily confined to potatoes grown on 

 the peat lands of California. 



Another series of inoculation experiments was carried out to ascertain 

 what temperatures were most favorable for the growth of the fungus in 

 the potato and at what temperatures no infection would result from an 

 inoculation. In these experiments inoculated potatoes were kept at 

 seven different temperatures, varying in 5-degree intervals from 5 to 35 

 C. Seventy potatoes of the Burbank variety were used. Forty of these 

 potatoes, those intended for the lower temperatures, were kept in the ice 

 box at about io° C. for 24 hours before inoculation, so that their tempera- 

 ture at the time of inoculation would be more nearly that at which they 

 were to be maintained during the experiments. For the inoculations 



