Oct.8.i93i Temperature and Humidity Studies of Fusaria Rots 67 



Link (9), making comparative studies of Fusarium oxysporum and 

 F. trichothecioides found that both were capable of producing a rot of 

 the potato tuber and that F. trichothecioides produced a typical dry- 

 rot. F. oxysporum produced a softrot of the whole tuber except under 

 cold, dry conditions, when a drjn-ot was produced. He ran his experi- 

 ments at controlled temperatures ranging from 1° to 30° C. in an 

 almost saturated atmosphere. 



Pratt {16) found that Fusarium radicicola behaved much the same as 

 F. oxysporum, and he concluded from storage experiments that the 

 tuber-rot caused by this organism does not make any progress in storage 

 at a temperature of 48° F. (8.8° C.) or below. 



In general, then, it can be said that a high temperature favors the 

 production of tuber-rots by all three of these Fusaria, although Fusarium 

 trichothecioides appears to be able to produce a rot at lower temperatures 

 than the other two. High humidities also appear to favor the produc- 

 tion of tuber-rot. With the exception of the paper of Jamieson and 

 Wollenweber {8) all the evidence points toward an increase in rotting 

 with an increase in humidity. 



TEMPERATURE RELATIONS IN PURE CULTURES 



A review of the literature shows a general conformity of results re- 

 garding the relation of temperature to the growth of Fusarium oxy- 

 sporum. Link (9) by making dry-weight determinations of growth in 

 liquid media found 30° C. to be the optimum for growth. Edson and 

 Shapovalov (5), working with Petri-dish cultures, obtained the same 

 optimum. They reported a maximum temperature of 37 C, where the 

 spores changed to chlamydospores ; they did not observe growth at 5° C. 

 Humphrey (7) gives 4° C. as the minimum temperature for certain 

 strains of F. oxysporum.. 



The writer, working with three strains of Fusarium oxysporum and 

 using the same methods for measuring growth, obtained somewhat 

 similar results to those reported by Edson and Shapovalov (5). The 

 minimum temperature for growth was 9.5° C, no growth taking place at 

 the next lower temperature of 7° C. The maximum temperature was 

 37.5° C, where there was a very slight growth. 



Fusarium trichothecioides is apparently unable to grow at 30° C, 

 which is the optimum temperature for F. oxysporum. Link (9) found the 

 greatest growth of F. trichothecioides in liquid potato extract media at 

 the end of 20 days to take place at 12° C, with no growth present at 30° 

 C, although the organism was capable of living in the potato tuber at 

 that temperature. Edson and Shapovalov (5) obtained a much higher 

 optimum for F. trichothecioides; they found the greatest growth took 

 place at 25*^ C, with a sharp drop to the maximum temperature at 30° C, 

 where germination of spores took place but no growth of mycelium. 



