3H 



FUNGOUS DISEASES OF PLANTS 



Fig. 146. Cercospora Gossypina: an 

 Isolation Culture 



XX. CERCOSPORA: OTHER SPECIES 



Parallel cultures on diverse culture media of a number of 

 species on related hosts would be of special interest. As in the 



case of Phyllosticta, subse- 

 quently discussed, numerous 

 leaf spots are produced by 

 members of this genus Cerco- 

 spora. Very few cross inocula- 

 tions have been made, and little 

 is really known concerning the 

 limitations of species. When 

 the host plants are different, 

 minor variations in the size, 

 color, septation, etc., of spores 

 and conidiophores, or in the 

 macroscopic appearances of 

 spots, are generally employed 

 in distinguishing species. 

 Among many other species the following upon important hosts 

 may be mentioned. 



Cercospora Viticola Sacc. This fungus produces a spot known 

 as grape leaf blight. It has not been productive of serious damage 

 except during unusually moist seasons. The 

 spots are first evident on the lower surface of 

 the leaf, and it is also upon this surface that 

 the conidiophores are developed. Upon Am- 

 pelopsis quinquefolia a Cercospora is more 

 commonly found, but apparently no com- 

 parative study of these different forms has 

 been made. 



Cercospora circumscissa Sacc. is one of the 

 shot-hole-producing leaf fungi of the genus 

 Prunus. It occurs on some of the native 

 American as well as cultivated species of 

 plums and cherries (Fig. 147) and on the nec- 

 tarine and peach. It is, however, not so important from a patho- 

 logical point of view upon most of these hosts as Cylindrosporium 



Fig. 147. Cercospora 

 circumscissa: Spots on 

 Almond. (After Pierce) 



