Pathil 



PATHOG^ICITY OF NEMATODES IN RELATION TO KOCH'S POSTULAT'^2 

 W. B. Moiintain 



One aspect of research which has intrigued me for a niimber of years and 

 which is basic to the scientific method is that of establishing the 

 precise conclusions we are justified in deriving on the basis of our 

 research. It is my belief that over the years in Plant Nematology there 

 has been a tendency, perhaps unintentional, to try to define the role of 

 a nematode in a plant disease with more precision than one should attempt 

 to do with the data presented. 



Also, speaking with the background of a Plant Pathologist, I am convinced 

 that many nematode papers which have appeared in print have not been held 

 in particularly high regard by Plant Pathologists simply because the 

 writers used, in too haphazard a manner, plant pathological terms which, 

 in that discipline, have precise connotations and should be used only 

 when certain definite facts have been established. I might say here that 

 great credit and respect are due to the earlier Plant Pathologists who 

 developed with clarity and precision many of the fundamental concepts in 

 plant pathology and particularly for adapting to plant pathology the 

 highly developed and critical standards of general pathology which origi- 

 nated in the late nineteenth and early twentieth centuries. 



I want to refer particularly to the concepts of pathogen and pathogenicity. 

 It is my belief that these words are being used much too loosely in plant 

 nematology, and I might say in other phases of plant pathology, as well. 

 In connection with the loose usage of such technical words as pathogen 

 and pathogenicity, the report of the Committee on Technical Words of the 

 American Phytopathological Society issued at the 31 'st Annual Meeting is 

 just as meaningful today as it was sixteen years ago. "We feel that some- 

 thing should be done to aid in reducing loose use of technical words. 

 Loose usage is not the same as different usage. An author may use words 

 in a sense quite different from the usual, but, if his concepts are 

 clearly explained and his meanings explicity defined, consistent with 

 each other and consistently applied by him, he cannot be accused of loose 

 usage . " 



I wonder if we might be able to eliminate loose usage of the words patho - 

 gen and pathogenicity by carefully evaluating our concept of these words, 

 by placing restrictions on their use and meaning, and, if necessary, by 

 erectir.g new concepts in order that we might be able to define with pre- 

 cision the implications of our research. 



I would like to refer to a typical example of loose usage of the word 

 pathogenicity in an otherwise excellent research paper. In a scientific 

 paper which appeared recently, the writer concluded that he had proven 

 the pathogenicity of a particular nematode with reference to a particular 

 crop. The nematode, which is an ectoparasite, was reared in soil upon 



