Oct. 8,1921 Temperature and Humidity Studies of Fusaria Rots 69 



No. I. — Fusarium oxysporum, isolated by the author from browned 

 vascular bundles of potatoes and identified by H. W. Wollenweber and 

 numbered at Washington as 3377. '^-''^ r. 1 ;■;■. 



No. 8. Fusarium oxysporum, obtained from C. W. Carpenter of the 

 United States Department of Agriculture, No. 3395. 



No. 32. — Fusarium oxysporum, obtained from G. K. K. Link, of the 

 University of Nebraska, as No. 3345a. 



No. 28. — Fusarium. irichoihecioides obtained from G. K. K. Link. 



No. 31. — Fusarium irichoihecioides, obtained from A. C. Pratt of the 

 United States Department of Agriculture. 



No. 29. — Fusarium radicicola, obtained from A. C. Pratt and numbered 

 716. 



METHODS 



In all inoculation experiments with tubers, potatoes which were of one 

 variety, of the same age, and had been kept under the same storage con- 

 ditions were carefully selected for uniformity of size, type, and freedom 

 from wounds. The stem ends always were cut and examined for natural 

 infection, and all tubers showing vascular discoloration were discarded. 

 The tubers were always treated with formaldehyde or mercuric chlorid 

 and washed in sterile distilled water. 



The inoculations were made by wounding the epidermis, usually by 

 stabbing to a depth of 3 mm. with a sterile scalpel. The inoculum was 

 introduced in various ways as outlined in the experiments. 



Experiment i, December, 1915- — Potato tubers of the Up-to-Date 

 variety were inoculated by wounding the tubers and then dipping them 

 in a water suspension of spores, wrapping in sterile waxed paper, and 

 placing in moist chambers at 25° C. Controls were treated in the same 

 way, being dipped in sterile water. Results were taken 18 days later. 



Set No. I. Four tubers inoculated with Fusarium. oxysporum, No. i. 

 All tubers completely rotted. The two control tubers remained sound. 



Set No. 2. Four tubers inoculated with Fusarium oxysporum, isolated 

 from infected tubers in storage. All tubers showed a complete wetrot; the 

 tissue was soft and of a light brown color; a large cavity was present in 

 each tuber containing masses of white mycelium. At the point of inocu- 

 lation there was a granular mass of hyphae and starch grains separated 

 from the rest of the tissue. Control tubers remained healthy. 



Set No. 3. Four tubers inoculated with Fusarium oxysporum, isolated 

 from wilted potato vines. All tubers showed a dark brown dryrot pro- 

 gressing only a short distance from the point of inoculation. Controls 

 remained healthy. 



Reisolations were made from all the rotted tubers, and Fusarium oxy- 



sporufn was recovered in every case. No bacteria or secondary invaders 



were found in any of the tubers. These results show that F. oxysporum 



is capable of producing a rot of the tuber in a saturated atmosphere at 



54818°— 21 2 



