22 Walter H. Burkholder 



A DISEASE OF THE BEAN CAUSED BY A VARIETY OF PHYTOMONAS 



PHASEOLI 



(Var. fuscans n. var.) 



In August of 1924, specimens of diseased bean leaves were collected in a 

 garden at Montreux, Switzerland. The variety of bean was unknown, but 

 it was of the green-pod type; and the lesions on the leaves of the plants 

 were typical of those caused by Phytomonas phaseoli. The spots varied 

 in size, were brown and necrotic, and were surrounded by a yellowish 

 border. In December of the same year, attempts were made to isolate an 

 organism from these specimens although the leaves were in a very dry 

 condition. A part of a lesion was macerated in sterile water and dilution 

 plates were made. In all the plates, yellow, rapidly growing bacterial 

 colonies appeared, very much like Phyt. phaseoli in appearance except for 

 one characteristic. The agar medium about all the colonies became, after 

 a week's time, a distinct brown in color. It was thought at first that the 

 organism produced a water-soluble brown pigment which dissolved through- 

 out the neighboring medium. This interpretation, however, was found 

 later to be incorrect. Further dilution plates were made with the patho- 

 gene to separate it from any contaminating organism; a single colony was 

 transferred to a tube and its pathogenicity on the bean was proved. A 

 reisolation then was made from one of the infected plants, and the culture 

 was saved for further work. 



In August, 1927, green-bean pods were obtained in a market at Lucerne, 

 Switzerland, which showed dark green, water-soaked spots apparently due 

 to a bacterial invasion. Later, from these spots an organism was isolated 

 similar in appearance to the one just described. The colonies were yellow 

 and the surrounding medium became a distinct brown in color. This 

 second isolation of this bacterium appeared to be an indication that the 

 pathogene was not uncommon in Switzerland, and from the nature of the 

 lesions observed it caused a disease similar to the blight due to Phyt. 

 phaseoli. The pathogenicity of this organism was tested by inoculating 

 it into a bean plant, and after infection took place it was reisolated and 

 saved for further work. 



Miss Florence Hedges informed the writer that she also had isolated 

 what appeared to be the same organism from diseased bean seed which 

 had been imported from South America. The pathogene probably is wide- 

 spread, but, owing to its similarity to Phyt. phaseoli, has been overlooked. 



INOCULATION EXPERIMENTS 



On the bean 



Inoculation experiments were conducted on Wells' Red Kidney plants in 

 a greenhouse with a temperature of approximately 80° F. While the 

 organism never completely lost its pathogenicity in pure culture, its vim- 



