Feb. i6, 1920 Temperature Relations of Potato-Rot Fungi 523 



indicate that while if sufficient moisture is provided the spores and the 

 mycelium of this organism remain alive at 30° C, they do not survive 

 exposure for several days to a temperature of 35° or higher. 



Several potato agar plates inoculated in the manner described above 

 were kept at 30° and 35° C. for 7, 8, 11, and 14 days and then removed 

 to room temperature. No growth ensued in any of these plates. 



Nine beef-broth tubes were inoculated heavily with the spores of 

 Verticillium and placed in incubators set at 25°, 30°, and 35° C. At the 

 end of two days spores germinated at the two lower temperatures and 

 formed growth visible to the unaided eye. Spores at 35° remained 

 unchanged; but when one tube was brought to the laboratory, germina- 

 tion took place and growth developed. Two additional tube cultures 

 were kept at the original temperature two weeks and then removed to 

 the laboratory. No growth resulted in these cultures. 



Thirty-five tubers selected in the field from hills badly affected with 

 Verticillium-wilt in northern Maine were incubated at 25°, 30°, 35°, 37°, 

 and 41° C, with 7 tubers to each compartment. After 13 days 2 tubers 

 were taken from each lot, and cultures were made from the discolored 

 stem ends. Twelve plantings from the material kept at the two lower 

 temperatures yielded 5 cultures of V. albo-atrum while 7 remained sterile. 

 No culture was obtained from material exposed to 35° or higher. Two 

 of the remaining tubers of each lot were incubated 22 days longer, or 

 for a total period of 35 days. Isolations from the 25° and 30° lots gave 

 6 cultures of Verticillium out of 12 plantings. The lots at 35° and 37° 

 yielded sterile cultures. The tubers held at 41° were dead and blackened 

 and were discarded. The remaining 3 tubers of each lot were kept for 

 an additional 1 1 days. Isolations were made from the material held at 

 30°, 35°, and 37°. Three out of 9 plantings from the 30° material gave 

 cultures of V. albo-atrum, while plantings from the tubers stored at 

 higher temperatures proved sterile. Thus, the results were uniformly 

 identical; the fungus survived exposure to 30°, but in no single case 

 survived the exposure to 35°, 



Incubation of freshly prepared culture plates at a properly chosen 

 high temperature may serve as a useful practical method for the differ- 

 entiation of the fungi which possess strikingly different maximum 

 temperatures but which are otherwise very similar in cultural character- 

 istics, particularly if they do not readily yield high cultures. Such is 

 the case with Fusarium coeruleum. and F. radicicola. They resemble 

 each other very closely in color reactions on standard culture media, yet 

 it usually requires a considerable length of time before typical spores of 

 the former can be secured. If plate cultures placed at 35° C. for two or 

 three days show no growth whatever, there is perfectly safe ground to 

 assume that the fungus is not F. radicicola. This test may be very 

 helpful when a prompt identification is desired or when additional 

 evidence to support a conclusion is being sought. 



