THE BACTERIAL DISEASES OF THE BEAN 

 A COMPARATIVE STUDY 



Walter H. Burkholder 



The purpose of the investigation here reported was to separate and to 

 distinguish, among the various diseases of the bean (Phaseolus vulgar-is L.), 

 those that are of bacterial origin. A number of such diseases occur on 

 this crop, with symptoms for the most part similar and in some cases 

 apparently indistinguishable from one another. The questions naturally 

 arise as to how many of these diseases there are, which ones are causing 

 economic losses to the crop, and how they may be recognized one from 

 another. A knowledge of these phases of the subject is essential for the 

 investigator before further work can be done effectively on any one of 

 the diseases, since he must be able to recognize the disease with which he 

 is working and to eliminate or be aware of the remaining bacterial diseases 

 in his field of experimentation. 



The bacterial disease of the bean caused by Phytomonas phaseoli has 

 been recognized for a considerable period of time, but the diseases caused 

 by Phyt. flaccumfaciens and Phyt. medicaginis var. phaseolicola have been 

 known only during the past four or five years. Since these last-named 

 diseases have been described, no comparative study has been made of the 

 three; and, because they are so similar in many respects, confusion has 

 arisen as to their distinctiveness and as to their identity. It was hoped in 

 undertaking this investigation to clear up some of this confusion. In the 

 progress of the work, however, it soon was found that still other bacterial 

 diseases of this crop exist which further complicate the problem. Six 

 distinct diseases have been recognized in this investigation, and in certain 

 of these the pathogene appears to be composed of several different races. 

 Consequently the entire problem of the bacterial diseases of the bean is 

 more complicated than former^ it was thought to be. 



In separating the various diseases and distinguishing them one from 

 another, the work naturally falls into three parts: first, the symptomatology 

 of the diseases on the bean ; secondly, the host range of the pathogenes ; and 

 thirdly, the etiology, a study of the morphology and the cultural charac- 

 teristics of the pathogenes. Other phases of the problem are numerous 

 and important, but they are not phases that would facilitate the separation 

 of these diseases which are under consideration. In presenting each disease 

 separately in this memoir, the above three divisions of the problem have 

 been dealt with mainly. What is known concerning the life history of the 

 organism, however, has not been neglected. In treating this problem in 

 such a manner it has seemed justifiable to duplicate certain of the previous 



