522 



Journal of Agricultural Research 



Vol. XVIII, !io. ic 



Table; I. 



-Seasonal prevalence of Fusarium oxysporiim and Verticilliuni albo-airum 

 under the climatic conditions of the vicinity of Washington, D. C. 



Treatment of seed tubers. 



Inoculated with F. oxy- 

 sporum a few days before 

 planting 



Inoculated with V. albo- 

 atrum a few days before 

 planting 



Control tubers, uninocu- 

 lated 



29 



IS 



It appears from this table that there were more tubers infected with 

 Fusarium oxysporum in the early crop grown at higher temperature than 

 in the late crop grown at lower temperature, and vice versa with Verticil- 

 Hum albo-atrum. The presence of the Fusarium infection in the control 

 tubers indicates that, probably, the largest part of it came from the soil, 

 while the infection of the new tubers with Verticillium came exclusively 

 from the seed. Verticillium was absent both in the control plot and in 

 the Fusarium plot of each crop. 



The fact that the growth of potato fungi was seriously inhibited at or 

 somewhat below 5° C. is of a considerable practical importance. Although 

 the curves showing the temperature relations of these fungi in pure cul- 

 tures may not always coincide with those which would designate their 

 development in the host tissues, yet one may be reasonably certain that 

 a temperature of about 40° F. or slightly below will suffice to check the 

 spread of the Fusarium potato tuber-rots in storage. Brooks and Cooley's 

 studies^ show that the growth of apple-rot fungi is retarded by low tem- 

 peratures to a much greater degree on the host itself than on artificial 

 media The requisite temperature for successful infection is, therefore, 

 higher than the minimum temperature necessary for growth in cultures. 



High temperature treatment of the seed tubers to effect the death of 

 invading parasites suggests itself as a thing which may deserve certain 

 attention. In view of the thermophylic habit of Fusarium oxysporum, 

 the possibility of application of sufficiently high temperature to cause 

 the death of the parasite and not to injure the vitality of the tuber is 

 quite remote. The case with Verticillium albo-atrum is, however, more 

 hopeful. Certain preliminary experiments conducted by the writers 



• Brooks, Charles, and Cooley, J. S. Op. CIT. 



