Feb. 16, 1920 Temperature Relations of Potato-Rot Fungi 



515 



The optimum temperature divides the potato fungi into two groups. 

 One, consisting of four Fusaria and two Verticillia, has its optimum in 

 the neighborhood of 25° C; and the other, comprised of F. oxysporum 

 and F. radicicola, has its optimum in the vicinity of 30°. As shown bv 

 Brooks and Cooley,^ the optimum temperature for F. radicicola on corn- 

 meal agar is the same as stated here for cultures on potato agar — that is, 

 30°. After 7 days of incubation at this temperature the two latter para- 

 sites practically covered the plates. F. discolor var. sulphureutn and F. 

 trichothecioides produced the next largest amounts of growth, and the 



DIAMETER OP COLONIES IN MILLIMETERS. 



c^ s /'o /'s £0 2S JO Js- ^=^. 



Fig. 3.— Graph showing the rate of growth of Fusarium eumardi on potato agar at different temperatures 



remainder formed colonies measuring on the average only 22 to 32 mm. 

 in diameter. 



The maximum temperature at which growth occurred in Fusarium 

 coendeum, F. trichothecioides , and Veriicillium alho-airum No. 427 was at 

 or slightly below 30° C. Germination took place with F. trichothecioides 

 at 30°, but no growth visible to the unaided eye was formed. The other 

 two fungi did not even germinate at this temperature. F. discolor var. 

 sulphureum, F. eiCmartii, and V . albo-atrwm No. 426 were not able to 

 germinate at 35°. The Verticillium spores remained unchanged, but 

 the normal typical spores of the two Fusaria were gradually changed to 

 chlamydospores. Similar transformation of the spores of F. oxysporum 

 occurred at 37° and of F. radicicola at 39°. 



156105*— 2( 



1 Brooks, Charles, and Cooley, J. S. Op. ciT., p. 156. 

 2 



