CLIMATIC CONDITIONS AS RELATED TO CERCOSPORA 



BETICOLA ^ 



By Venus W. Pool, Assistant Pathologist, and M. B. McKay, Scientific Assistant, 

 Cotton and Trtick Disease Investigations, Bureau of Plant Industry 



INTRODUCTION ^ 



Climatic conditions of both mnter and summer bear an important 

 relation to the vitality and development of Cercospora heticola. During 

 cold weather certain conditions enable the fungus to overwinter, while 

 certain other conditions are inimical to its growth, a fact which has an 

 important bearing on the control of the disease, as the earliest infections 

 on growing sugar beets {Beta vulgaris) originate from the overwintered 

 fungus. In the early summer, after infection occurs, temperature, rela- 

 tive humidity, rainfall, and wind directly affect the development of the 

 fungus, the rapidity of conidial production, and subsequent infection. 



OVERWINTERING 



From the investigations here described it seems evident that under 

 ordinary field conditions of winter the conidia of C. heticola usually live 

 but a short time, although under ordinary herbarium conditions desic- 

 cation takes place only after exposure for several months. The sclerotia- 

 like bodies (fig. i , A, a), or masses of mycelium, the most resistant part 

 of the fungus, which are embedded in the infected areas of the leaf blades 

 and petioles, however, live over the winter under favorable conditions and 

 in the spring produce conidia from the remnants of the old conidiophores 

 (fig. I, A, h), or both conidiophores and conidia (fig. i, A, c) may be 

 formed anew. For the purpose of making direct microscopical observa- 

 tion of such development sections of infected tissue which had been 

 stored throughout the winter under favorable conditions were placed in 

 hanging-drop cultures of bean agar. New conidiophores (fig. i, B, h) 

 grew from the masses of embedded mycelium, and although somewhat 

 abnormal they produced rather typical conidia (fig. i, B, c), thus show- 

 ing that such material may be a source of early infection of growing 

 plants. 



> The investigations were carried on entirely in the field. Preliminary work was conducted during 191 1 

 and 1912 at Rocky Ford, Colo. The detailed data were collected during 1912 and 1913 at Rocky Ford, 

 which is in the Arkansas Valley of Colorado, a semiarid region under irrigation, and during 1914 near 

 Madison, Wis., where the rainfall and average humidity were greater. 



2 The writers are indebted to Mrs. Nellie E. Fealy, of the Bureau of Plant Industry, for aid in editing 

 and revising the manuscript. 



Journal of Agricultural Research, Vol. VI, No. i 



Dept. of Agriculture, Washington, D. C. Apr. 3, 1916 



cr G— 7S 



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