TEMPERATURE RELATIONS OF CERTAIN POTATO-ROT 

 AND WIIvT-PRODUCING FUNGI 



By H. A. Edson, Pathologist, and M. Shapovalov, Assistant Pathologist, Cotton, 

 Truck, and Forage Crop Disease Investigations, Bureau of Plant Industry, United 

 States Department of Agriculture 



INTRODUCTION 



Plant pathologists are well aware of the fact that certain parasitic 

 organisms which seriously injure growing crops in one geographical lat- 

 itude remain practically harmless in another. It seems reasonable to 

 assume that the temperature of the different regions, aside from other 

 climatic conditions, may greatly influence the occurrence of these para- 

 sites. As shown by Fawcett in his recent work,^ a correlation exists 

 between the cardinal temperatures of certain fungi in cultures and their 

 geographical distribution and seasonal occurrence. 



Moreover, the importance of properly regulated low temperatures for 

 cold storage is fully recognized, not only for the purpose of controlling 

 physiological and chemical changes, but also in order to check the prog- 

 ress of parasitic diseases. On the other hand, certain high temperatures 

 are successfully employed not only to regulate ripening and sweating 

 processes but also to effect the death of the invading parasites without 

 lowering the vitality of the host. 



There is, however, a regrettable lack of exact information regarding 

 the temperature relations of different potato parasites. The following 

 data secured in experiments with pure cultures of some of the most com- 

 mon potato-rot and wilt fungi may prove to be interesting and significant. 

 They explain to a certain degree the predominance of these organisms 

 in definite regions and definite seasons. They also permit certain prac- 

 tical conclusions regarding the temperatures which may control or elim- 

 inate these fungi. 



CULTURES AND METHODS EMPLOYED 



The cultures used in the tests with statements concerning their or- 

 igin and time of isolation are listed below. As will be seen later from the 

 graphs, the two strains of Verticillium, one from the South and the other 

 from the North, showed distinctly different thermal behavior. Only 

 one strain of each species of Fusarium was used in all experiments. 



Fusarium coeruleum (Lib.) Sacc. (Culture No. 201).^ Isolated by C. W. Carpenter 

 in March, 1915, from potato tubers grown in the State of New York. 



' Fawcett, H. S., preliminary note on the relation of temperature to the growth of certain 

 PAR.\smc FUNGI IN CULTURES. Ill Johns Hopkins Univ. Circ. 293 (n. s. no. 3) p. 193-194. 1917. 

 2 Numbers accompanying each culture refer to the writers' catalogue. 



Journal of Agricultural Research, Vol. XVIII, No. 10 



Washington, D. C. Feb. 16, 1920 



tm Key No. G-183 



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