60 Walter H. Burkholder 



were circular in outline except where anastomosing occurred. Judging 

 from the pod, the bean was of a Refugee green-pod type. A number of 

 these pods were collected and dried, and later, in October of the same year, 

 an attempt was made to isolate an organism. In making these isolations, 

 small parts of the lesions were macerated in sterile water, and dilution 

 plates were poured from these. Bacterial colonies, white to cream yellow 

 in color and producing a green fluorescent pigment, appeared in profusion 

 in all the plates. In the following experiments, three different strains 

 isolated from three different pods were used. The strains were, however, 

 practically identical. 



In testing the pathogenicity of these organisms, bean seedlings were 

 inoculated at the cotyledon node by pricking and introducing the bacteria 

 at the same time. Two days after the seedlings were inoculated, infection 

 occurred, and within four days the plants toppled over and were dying. 

 The virulence of the organism was extremely high. In no other case under 

 observation had a pathogene acted with such rapidity. For further work 

 with the pathogene, reisolations were made of the three strains and the 

 pathogenicity of each was again tested. 



INOCULATION EXPERIMENTS 



On the bean 



The disease produced by this pathogene has never been studied nor 

 observed in the field on the living host. After the first specimens were 

 collected in the market of Lucerne, all observations and experiments 

 were conducted on plants artificially inoculated. This was done in a 

 greenhouse under constant temperature control of approximately 80° F. 

 The variety of bean used was Wells' Red Kidney. The striking pecu- 

 liarities of the disease were observed under these conditions, and they 

 are such as to set it apart from any of the other bacterial blights of the 

 bean. 



In general, this Swiss organism appears to be the most virulent of the 

 bacterial pathogenes treated in this memoir. At least, its incubation 

 period is the shortest, and its invasive ability for the first few days is the 

 greatest. When inoculated into a young plant, the organism spreads 

 rapidly and invades all the tissues within its path, killing them and 

 producing a necrotic lesion. Infection appears in about two days. The 

 extent of the invasion, however, is reached possibly by the fifth day or 

 in a little less than a week. Then the invasive ability of the pathogene 

 apparently ceases altogether. Whether this is owing to the organism 

 or is a host reaction has not been determined. 



The lesion on the main stem of a young plant will extend probably less 

 than an inch above and below the point of inoculation. This depends to 

 a certain extent on the age and the succulency of the tissues involved. 

 With the killing of the cells throughout the main stem, all parts of the 



