Journal of Agricultural Research 



Vol. VI, No. s 



the sugar and the soHd residue for the starch determinations. The 

 effect of three species of Fusarium, F. oxysporum, F. radicicola, and 

 F. coeruleum, on the starch and sugar content of sound and rotted 

 quarters of the same tubers was studied. The data obtained from the 

 determination of the sugars are shown in Table VIII. 



Table VIII. — Reducing sugar and sucrose content of the sourid and rotted quarters of 



potatoes 



[Expressed as percentage of the original wet weight] 



Species of Fusariiun and potato No. 



Reducing sugar. 



Rotted quarter. Sound quarter. 



Sucrose. 



Rotted quarter. Sound quarter, 



Infected with Fusarium oxy- 

 sporum: 



160 



159 



158.... , 



Infected with Fusarium coeru- 

 leum: 



149 



150 



151 



Infected with Fusarium radi- 

 cicola: 



32 



26 



34 



41 



0.66 



.67 



1.03 



39 

 66 



24 

 19 

 09 



42 



In Table VIII it may be seen that all three species of Fusarium used 

 the sugars. In most cases practically all the sugar had disappeared from 

 the rotted portion, the cane sugar being utilized almost if not quite as 

 completely as the reducing sugars. That the fungi could use disaccharids 

 directly — that is, without breaking them down to their constituent 

 monosaccahrids — seemed unlikely. It was therefore probable that the 

 fungi secreted enzyms which were capable of hydrolyzing cane sugar, 

 and possibly maltose also. To determine this point, tests were made 

 for sucrase and maltase in extracts of the mycelium of F. oxysporum and 

 F. radicicola. The fungi were grown for about three weeks or until a 

 thick mat of myceUum was formed on potato extract. The felt was then 

 separated from the liquid, ground up in a mortar and digested for 48 

 hours under toluol. The extract was filtered off and portions of it added 

 to solutions of the sugars of known concentration. Controls of the boiled 

 extract were also prepared. After the preparations had been allowed 

 to stand overnight at laboratory temperature the amount of reducing 

 sugar was determined. It w^as found that in the preparations of un- 

 boiled extract the sugars, both sucrose and maltose, were inverted almost 

 quantitatively. The boiled extracts were practically without effect. It 

 is evident then that the two fungi secrete both sucrase and maltase. 



