JOfflAL OF AGRICETIAL ffiSEARCH 



Vol. XV 



Washington, D. C, October 28, 1918 



No. 4 



PLASTICITY OF BIOLOGIC FORMS OF PUCCINIA 



GRAMINIS 



By E. C. Stakman, Head of the Section of Plant Pathology, Division of Plant Pathol- 

 ogy and Botany, Department of Agriculture, University of Minnesota,'- F. J. Piemeisel, 

 formerly Scientific Assistant, and M. N. LEvinE, Field Assistant, Office of Cereal BOTANICA 

 Investigations, Bureau of Plant Industry, United States Departinent of Agriculture OAkUBN. 



COOPERATIVE INVESTIGATIONS BETWEEN THE AGRICULTURAL EXPERIMENT 

 STATION OF THE UNIVERSITY OF MINNESOTA AND THE BUREAU OF PLANT INDUS- 

 TRY OF THE UNITED STATES DEPARTMENT OF AGRICULTURE ^ 



INTRODUCTION 



Ever since the discovery of biologic forms of Puccinia graminis Pers. 

 by Eriksson (5) ^ there has been much speculation as to the degree of 

 fixity of these forms. Eriksson (6, p. 657) expresses the opinion that, on 

 account of host and climatic influences, the forms may gradually change. 

 His conception of a biologic form is that it is the result of an adapta- 

 tional tendency. Magnus {13, p. 366) seemed to be of the opinion that 

 biologic forms are the result of association with the particular host plants 

 which they attack. Dietel (4) and others held essentially similar views. 

 In general these assumptions have been considered reasonable. 



Ward {22, 23), as a result of exhaustive investigation of the brown rust 

 of bromes Puccinia dispersa Erikss., concluded that biologic forms of 

 this rust could be changed parasitically by association with the proper 

 host plants. He found that, whereas it was often impossible to transfer 

 the rust directly from one species of Bromus to another species, this 

 result could sometimes be accomplished by infecting a third species on 

 which the rust acquired the capability of infecting the normally immune 

 species. Such species he designated bridging species. His opinion 

 appears to have been that taxonomic relationships among the species of 

 Bromus were the determining factor. If, for example, the rust on a 

 given species. A, could not be transferred directly to another species, C, 

 it might be transferred to B, intermediate taxonomically between A and 

 C. The species B then changed the rust sufficiently to enable it to infect 

 C. Having once established itself on C, it was thenceforth capable of 



' On leave. 



2 Published, with the approval of the Director, as Paper 127 of the Journal series of the Minnesota Agri- 

 cultural Experiment Station. 

 ' Reference is made by number (italic) to " Literature cited," p. 250-251. 



o 



IXJ 



Journal of Agricultural Research, 



Washington, D. C. 



pz 



(221) 



Vol. XV, No. 4 

 Oct. 28, 1918 

 Key No. Minn.-33 



