CHAPTER XII 



Inoculations with Bacteria Causing 

 Plant Disease 



A. J. RiKER IN COLLABORATION WITH O. N. AlLEN, P. A. ArK, 



A. C. Hildebrandt, and E. M. Hildebrand 



INTRODUCTION 



The methods for studying the pathogenicity of bacteria in plants and 

 for making a few selected cognate investigations are briefly treated. 

 The procedures for handling certain organisms and for studying the 

 diseases they induce vary so widely that no given directions apply to 

 the group as a w^hole. The selected representative methods included 

 are given primarily as guides to the beginner and need modification 

 according to circumstances. Two excellent reviews have appeared 

 recently by Allen and Allen (1950) and Hildebrandt (1950). 



Difficulty in interpretation frequently is encountered from variations 

 in results that depend on the methods used. A given bacterial charac- 

 teristic may sometimes be positive when measured by one method and 

 be negative when measured by a slightly different technique. Students 

 should employ a known positive and a known negative as controls when 

 making critical determinations. The method used should always be 

 given or cited when a characteristic is listed, so that its validity can be 

 estimated by the reader. 



A number of topics discussed in Chap. X regarding bacteria path- 

 ogenic on animals are applicable to bacteria pathogenic on plants. These 

 include particularly (1) identification of the active agent as the bac- 

 terial cell or its products; (2) distinction between invasion and the 

 power to cause disease after entry; (3) variabihty in virulence of the 

 pathogen, which requires single-cell cultures, and in susceptibility of the 

 host, which frequently calls for plants with known genetic constitution, 

 when critical studies are involved; and (4) relations between reactions 

 induced in the test tube and in the host. 



28G 



