Apr. 3, 1916 



Climatic Conditions and Cercospora beticola 



23 



CONIDIA 



Thiimen (1886, p. 50-54) ^ believed that the spores of Cercospora beti- 

 cola are able to live for a certain length of time in the soil and retain their 

 viability and produce new infection, and Pammel (1891, p. 238-243) and 

 Massee (1906, p. 52-53) accord with this view. In the investigations 

 here considered it was found that when kept dry, as in the case of her- 

 barium material, the conidia remained viable for 8 months (Table I, 

 tests 10 to 13), but soon after that no growth occurred. Only rarely 

 were conidia found on the infected areas of the leaves which were exposed 

 to outdoor weather conditions, and such conidia seemed to lose their 

 vitality soon after harvest. No germination was found to take place 

 under optimum conditions in the case of conidia which had been thus 

 exposed from i to 4 months (tests 14 and 15). However, conidia occa- 

 sionally found on spots that had been well protected, for instance in the 

 interior of a pile of hayed beet tops, retained their viability for from 5 to 

 less than 12 months (tests 16 and 17). Since the coUidia are rarely found 

 after a short time even on infected material that has been well protected 

 and since they rarely germinate after being exposed outdoors for even i 

 month after harvest, it would seem that under ordinary field conditions 

 they play no important part in the overwintering of the fungus. 



Table I. — Viability of the conidia of Cercospora beticola as affected by desiccation 



SCLEROTIA AND MYCEUUM 



Various investigators have attempted to determine whether different 

 fungi live in the soil over winter and the manner in which they over- 

 winter. Treboux (191 4) found that the mycelia of several different rusts 

 overwinter on host material freely exposed to climatic conditions. Stew- 

 art (191 3) placed in boxes of soil potato leaves and tubers infected with 

 Phytophthora injestans, exposed them to outdoor winter conditions, and 

 found that plants grown on such soil developed no blight. However, 



' Bibliographic citations in parentheses refer to "Literature cited," p. 60. 



