74 



Walter H. Burkholder 



ETIOLOGICAL BASIS 



When it is desirable to be very positive concerning the etiological agent 

 of a bacterial disease of the bean, the isolation and determination of the 

 pathogene is essential. This is not a difficult task, since in certain media 

 the bacteria show considerable differences. Little need be said here 

 as to the technic of isolations. All the organisms grow well on beef extract 

 agar or on potato agar. In the lesions on the plants, the bacteria may 

 be found in abundance and in most instances apparently inhibiting all 

 secondary invaders. At least, by following the ordinary precautions 

 only a few contaminating colonies will appear on the plates. Dilution 

 cultures are usually more satisfactory than tissue plantings. 



The morphology of the respective pathogenes is not sufficiently charac- 

 teristic to be of much help in diagnostic work. One must rely on the 

 cultural reactions. In table 2 a few reactions are given which will suf- 



TABLE 2. 



Major Differences in the Cultural Reactions of Six Different Bac- 

 terial Pathogenes of the Bean (Phaseolus vulgaris) 



ficiently differentiate all of the organisms. The complete descriptions 

 on preceding pages of the memoir should be consulted also. The color 

 characters may be a little difficult to use, with the exception of the deep 



