Fusarium in Tuber Rot and Wilt of rotate 



31 



It should be noted here that F. trichothecioid.es when inoculated 

 into a tuber can grow at 30° C, while it cannot do so in artificial 

 media; and that F. oxysporum can survive a temperature of 1° C. 

 in artificial media, lint not in the tuber. 



TABLE IV 

 Condition of tubers at close of experiment 



Temperature 



Fusarium oxysporum Fusarium trichothecioides 



30° C. 

 25 : C 



12 



1° c... 



1° C. for two weeks, then 

 25° C. for two weeks 



-1°C 



— 1° C. for two weeks, then 

 25° C. for two weeks. 



All completely rotted; : Slight rot in some 



sprouts killed 

 All completely rotted; i All completely rotted; 



sprouts killed some sprouts killed 



All with very slight rot All completely rotted 

 No rot All with slight rot 



Slight rot in one tuber 

 No rot 



All completely rotted 

 No rot 



All completely rotted 



Discussion. — These results may, in pan at least, explain why 

 /'. oxysporum, even though it can attack parenchyma and rot tubers. 

 usually is not found in rotted tubers, while F. trichothecioides is. 

 The ability of the latter to make a faster initial growth at the 

 temperatures which prevail in the soil about digging time and in 

 well kept storage places is probably the determining factor in this 

 phenomenon. The experiments with tubers showed that / ; . tri- 

 chothecioides made a great increase in growth rate when transferred 

 from a low to a higher temperature. 



These temperature relations may also explain in part the fact 

 that we usually find F. oxysporum producing wilt under field con- 

 ditions, and lend support to the observations made by ( >rton (27), 

 who reports potato wilt induced by Fusarium spp. to be pre- 

 eminently a warm climate disease. F. trichothecioides can produce 

 wilt, but the temperature conditions in the soil are such as to favor 

 F. oxysporum, the maximum temperature of the former being 

 the optimum of the latter. Humphrey (15i, working in Washing- 

 ton on the tomato wilt induced by F. oxysporum, came to the con- 

 clusion that temperature differences in various parts of the state 

 were determining factors for the appearance and non-appearance 

 and severity of the disease. 



