JAMIESON AND WOLLENWEBER : FUSARIUM TRICHOTHECIOIDES 151 



cioides. Pure cultures of this same Fusarium were later obtained 

 from tubers produced upon a plant diseased thru inoculation. 



Further experiments are now being made to determine the most 

 favorable conditions under which the infection of F. trichothe- 

 cioides takes place. For this experiment sound healthy potato 

 tubers of Burbank and Early Ohio varieties were selected, dis- 

 infected and placed in inoculation chambers. Two methods of 

 inoculation were tried, one by stabbing the tuber with a thick 

 needle and inserting fungus mycelium and spores from a pure 

 culture of F. trichothecioides, the other by rubbing the surface with 

 a platinum loop bearing the fungus. The ten inoculation cham- 

 bers were then placed under different conditions of heat and mois- 

 ture and examined at definite intervals. Thus far, results from 

 this test indicate that of the two methods stabbing is the most 

 effective, altho infection follows the rubbing of the fungus on the 

 surface of the tubers. Discoloration of the tissue was noticed in 

 the inoculation chambers after ten days and this was followed by 

 a decay which penetrated into the tissue 2-3 cm. in twenty days. 

 Rapid discoloration of the tissue was observed in both moist and 

 dry chambers placed at a temperature of 10-12° C. In the drier 

 atmosphere however, there was a deeper penetration of the decay 

 into the tissue, than occurred at the same temperature under 

 increased humidity. Two months after inoculation, the potato 

 tubers were carefully examined and their appearance compared 

 to the diseased specimens sent in from the field. Externally and 

 internally the disease characteristics in field and laboratory speci- 

 mens were similar. The brown grayish spots on the outside of the 

 inoculated tubers frequently surround the "eyes," except in the 

 case of the stab inoculations where the discoloration spreads about 

 the wound. On the surface of the diseased tissue there is usually 

 an abundant growth of pinkish powdery mycelium in the moist 

 atmosphere, but very little of the external fungus growth in the 

 drier air. The discoloration caused by the penetration of the 

 fungus and extending several centimeters below the epidermis 

 varies from light to dark sepia brown in color, the darkest por- 

 tion forming a band which surrounds the cavities. In every 



