JOraALOFAGRIOlTDRALffiSEMCH 



DEPARTMENT OF AGRICULTURE 



Vol.. IV Washington, D. C, June 15, 1915 No. 3 



RELATION BETWEEN PUCCINIA GRAMINIS AND 

 PLANTS HIGHLY RESISTANT TO ITS ATTACK 



By E. C. Stakman, 



Head of the Section of Plant Pathology and Bacteriology, Division of Botany aiid Plant 



Pathology, Department of Agriculture, University of Minnesota 



INTRODUCTION 



The intimate relations between host plants and uredine parasites 

 were first carefully investigated by H. Marshall Ward. Ward (10, 12)^ 

 showed that the relation between the brown-rust of bromes (Pticcinia 

 dispersa Erikss.) and its host plants might be quite variable. When 

 normal infection took place, as Ward pointed out, a very fine adjustment 

 was made between host and parasite, resulting in a vigorous develop- 

 ment of the fungus without immediate serious injury to the host. Indeed, 

 the host seemed sometimes not only not to be injured for a long time but 

 even to be somewhat stimulated. However, in some cases the fungus 

 was found to kill some of the host cells very soon after gaining entrance, 

 and the fungus itself grew but little. A wide range of possibilities was 

 found in varying degrees of infection, establishing the general principle 

 that the success of infection depended largely on the closeness of sym- 

 biotic relations set up between the host and the parasite. 



Gibson (4) showed that the germ tube of a rust fungus might enter 

 practically any plant, but that after entrance it was unable to produce 

 haustoria and consequently could not live. She found that when 

 varieties of chrysanthemum resistant to Uredo chrysanthemi Roze were 

 inoculated with spores of this rust the host cells near the hyphae were 

 killed, the further growth of the hyphae being thereby inhibited. Mar- 

 ryat (5) found a similar condition existing between P. glumarum Er. 

 and Henn. and host plants partially immune to its attack. The writer 

 (8) has shown that various strains or biologic forms of P. graminis 

 Pers. may kill shortly after inoculation comparatively large areas of 

 tissues in host plants that exhibit a considerable degree of resistance 

 to the fungus. Unquestionably the host plant in such cases is often 

 hypersensitive to the fungus, since the fungus kills very early much of 



' Reference is made by number to "Literature cited." p. 198-199. 



Journal of Agricultural Research, Vol. IV, No. 3 



Dept. of Agriculture, Washington, D. C. June 15, 19'S 



(193) Minn.— 4 



