[newton] wheat stem RUST 155 



It is, therefore, quite evident that the plant pathologist must do 

 pioneer work in the analysis of biologic strains of rust before the 

 breeder can be assured of effective results in producing resistant 

 varieties of wheat. 



The investigation here reported attempts such an analysis. It 

 was begun at Macdonald College in 1918, and continued at the 

 University of Saskatchewan and the University of Minnesota, until 

 the present time (April, 1922). 



A cknowledgments 



The work was carried on under the auspices of the Honorary 

 Advisory Council for Scientific and Industrial Research of Canada. 

 Collections were facilitated by an appointment from the Canadian 

 Department of Agriculture in the summer of 1920. The writer wishes 

 to acknowledge the kind help received from Dr. E. C. Stakman and 

 Mr. M. N. Levine, Cereal Investigations, Bureau of Plant Industry, 

 at the University of Minnesota, and Professor W. P. Fraser, Dominion 

 Laboratory of Plant Pathology, at the University of Saskatchewan. 



Historical Summary 



The phenomenon of biologic specialization in rusts has for many 

 years attracted the attention of workers in pure and applied biology 

 because of the light which it throws on the parasitic behaviour of 

 fungi, and lately because of the practical application which may be 

 made by the establishment of a basis for rust resistance. 



Eriksson (15) was the first to show definitely that biologic 

 specialization occurs in cereal rusts. He worked with Puccinia 

 graminis Pers. and in 1894 showed that what was usually considered 

 as one species attacking all the common cereals in reality consisted 

 of several pathological strains or biologic races. 



This discovery stimulated much research, and various biologists 

 in Europe and the United States began work in earnest upon this 

 problem. The whole field of biologic specialization has been carefully 

 reviewed by Reed (49), and specialization in the cereal rusts by 

 Stakman (52) and a detailed review, therefore, is not given here. 

 Only those papers are reviewed which are directly relevant to the 

 present problem. 



Until 1916 the existence of biologic forms of P. graminis on wheat 

 was not suspected. During that year a form of stem rust was collected 

 by Stakman and Piemeisel (58) in the Palouse district of Washington 

 and Idaho to which certain varieties of wheat were almost immune, 



