PHYSIOLOGICAL SPECIALIZATION OF PARASITIC 



FUNGI 



GEORGE M. REED 



University of Missouri 



One of the important developments in plant pathology in recent 

 years has been the discovery of races of well-defined morphological 

 species of parasitic fungi which are restricted to particular hosts. 

 These specialized races can be distinguished from each other only 

 by their ability to grow on some host plants and not on others. It is 

 now well established that species of parasitic fungi, identical in their 

 structural features as found on a more or less wide range of plants, 

 may consist of numerous races or strains which differ in their capacity 

 to infect the various hosts. 



Apparently Schroeter (136), as early as 1879, was the first to call 

 attention to this phenomenon in connection with certain rusts on 

 Carex. It is, however, to Eriksson (34) that we are indebted for a 

 realization of the importance and significance of the host specialization 

 of fungous parasites and for the impetus to the numerous investiga- 

 tions devoted to this phase of plant pathology. Eriksson's demon- 

 stration of races of Puccinia graminis, P. glumariim, P. dispersa and 

 P. coronata, distinguishable from each other only on the basis of the 

 hosts that they are able to successfully attack, is the real starting point 

 for a general recognition of the phenomenon of host specialization of 

 fungous parasites. 



Various terms have been introduced to apply to these races or 

 strains which show no anatomical differences, but are distinguishable 

 only by their physiological behavior in the choice of hosts. Schroeter 

 (138), in 1893, suggested the term sister species {Species sorores). 

 Klebahn (76), in 1892, described them as hiologische Spezies. Rostrup 

 (121, 122), in 1894, suggested the term biologiske Arter, and, in 1896, 

 proposed another term hiologische Rassen. In 1894 Hitchcock and 

 Carleton (63) proposed the term physiological species. Eriksson (34), 

 in 1894, introduced the generally used expression Specialisierte Formen 

 or Jormae speciales. Magnus (96), in 1894, employed the term 

 Gewohnheitsrassen or adapted races. Marchal (97) applied the term 

 races speciali ees, while Ward (174), Salmon (123) and others have 

 used the expression biologic forms or biological forms. • 



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