UNITED STATES DEPARTMENT OF AGRICULTURE 



In Cooperation with the 

 Icwa Agricultural Experiment Station 



DEPARTMENT BULLETIN No. 1162 



Washington, D. C. T September, 1923 



THE ROLE OF THE GENUS RHAMNUS IN THE 

 DISSEMINATION OF CROWN RUST. 



By S. M. Dietz, Assistant Pathologist, Office of Cereal Investigations, Bureau oj 



Plant Industry. 1 



Page. 



Introduction 1 



Relation of Rhamnus species to the epidemi- 

 ology of crown rust 2 



Rhamnus cathartica 3 



Rhamnus lanceolata 12 



Rhamnus caroliniana 14 



CONTENTS. 



Page. 



Relation of Rhamnus species to the epidemi- 

 ology of crown rust— Continued. 



Rhamnus alnifolia 15 



Five less important species 16 



Summary 17 



Literature cited 18 



INTRODUCTION. 



That certain species of Rhamnus, or buckthorn, may serve as the 

 alternate hosts of crown rust (Puccinia coronata Corda) is well estab- 

 lished through the excellent contributions of De Bary (l), 2 Klebahn 

 (7), Eriksson (8), and others. The role that the alternate host may 

 play in the dissemination and development of an epidemic of crown 

 rust is not yet understood, however, because previous work had 

 been confined largely to laboratory cultural studies. Until recently 

 epidemiology studies have been impossible because of a lack of defi- 

 nite knowledge regarding the susceptibility of our American species 

 of Rhamnus and their geographic range in the chief oat-growing 

 sections of the United States. 



As early as 1894 Henning (5) observed that Rhamnus cathartica L. 

 was dangerous to oats because of its relation to crown rust. Some 

 years later, in 1912, in response to repeated recommendations that 

 R. cathartica be used as an ornamental shrub, Henning (6) stated 

 that it should not be planted, citing Germany, Denmark, and Uruguay 

 as examples of countries that have suffered epidemics of crown rust. 



'The investigations of crown rust, of which the research covered by this bulletin is a portion, are 

 conducted by the Office of Cereal Investigations, Bureau of Plant Industry, United States Department 

 of Agriculture, in cooperation with the department of botanv of the Iowa Agricultural Experiment 

 Station. The writer wishes to express his thanks to Dr. I. E". Melhns, plant pathologist of the Iowa 

 station, under whose immediate direction the investigation is conducted, for suggestions and criticisms 

 during the progress of the work and the preparation of the manuscript; also to Miss Florence S. Willey , 

 assistant pathologist at the Iowa station, and to the Office of Cereal Investigations, for assistance in gather- 

 big data and in arranging the material for publication. 



'The serial numbers (italic) in parentheses refer to " Literature cited," at the end of this bulletin. 



42199°— 23 



