5 68 



Journal of Agricultural Research 



Vol. VI, No. 15 



(34 to 35 ) the tubers were more than half-rotted at the end of nine 

 day^, and in four more days all but one were decayed throughout. At 

 the end of 20 days D. tubericola was isolated in pure culture from each. At 

 a lower temperature (12.2 to 13.5 ) all the tubers but one were per- 

 fectly sound at the end of 45 days. One tuber was half-decayed, and 

 yielded F. culmorum. 



The temperatures at which decay may be brought about by 5. rolfsii, 

 F. solani, and B. carotovorus were determined by the use of raw blocks 

 of dasheen. After discarding the blocks contaminated in their prepara- 

 tion, the remainder were divided into two lots, one of which was inocu- 

 lated with 5. rolfsii and the other with F. solani. Each of these lots was 

 divided into 6 groups of 10 tubers each and placed in different chambers 

 of the Altman thermostat and in the laboratory room, the temperatures of 

 which ranged as follows : 



Results with Fusarium solani. — In all the chambers except No. 5 

 (9.1 C.) growth started in two days. While there was some difference 

 in the general appearance of the growth in the different chambers, there 

 was nothing strikingly characteristic. At the lower temperatures there 

 was a slight reduction of hyphal growth compared with higher tempera- 

 tures, accompanied by the production of a salmon-orange color on the 

 blocks. At the higher temperatures, particularly in chambers 18 

 (28. 6°) and 19 (35. 3 ), abundant hyphae were produced. An accident 

 to chambers 18 and 19 at the end of 10 days terminated that part 

 of the experiment, but an examination of the tubes showed that the 

 blocks were completely decayed and typical spores of the causal organism 

 produced. The others were continued for 20 days longer. At the end 

 of that time no decay had taken place in chamber 5 (9.1 ), and no 

 spores were formed, though a slight discoloration of the blocks had taken 

 place. In all the other chambers the blocks were completely softened. 

 In the tubes exposed to room temperature (22.4 ) typical spores were 

 produced, while in chamber 6 (14.0 ) there were a few abnormal spores, 

 in No. 9 (18. 4 ) many. In general it may be stated that while decay 

 was complete in all chambers except in No. 5 (9.1 ) spore production 

 was better at the three higher temperatures. The results therefore seem 

 to indicate that tubers stored at the higher temperatures are more liable 

 to be decayed by F. solani than if stored at a temperature of 8° to io° 

 or lower. 



