80 Walter H. Burkholder 



the similarity is so great that a microscope is essential in detecting the 

 difference. However, there are certain dissimilarities between the two 

 types of lesions which should be noted. Sun-scald spots always are 

 found on the exposed surface of the bean pod, and they never show the 

 water-soaked appearance that occurs with the more common bacterial 

 diseases. In many cases, too, the sun scald appears on the pods over 

 the seeds. These spots are somewhat sunken, and may be of any shape 

 from rather irregular dashes to large spots more or less circular in outline 

 which often anastomose. In color they are brown to red-brown, accord- 

 ing to the variety of bean. 



GEOGRAPHICAL DISTRIBUTION OF THE VARIOUS BACTERIAL DISEASES 



OF THE BEAN 



The exact geographical distribution of the various bacterial diseases 

 of the bean is difficult to determine, since it is only recently that more 

 than one of these diseases has been recognized. In reports of plant- 

 disease surveys, as a rule the cause of a blight of beans has been referred 

 to Phytomonas phaseoli. Probably in the majority of cases this has been 

 correct, but since there is seldom a description of symptoms of the disease 

 accompanying such a report one can never be quite sure. Seldom if ever 

 is an isolation of the causal organism made to determine its appearance 

 in pure culture. In the following paragraphs the known geographical 

 distribution of the six bacterial diseases of the bean here considered is 

 given. The actual distribution is much more extended than that re- 

 corded here, since there have been reports of bacterial diseases of the bean 

 in countries not mentioned in this account. From such reports, however, 

 there would be some difficulty in determining which bacterial pathogene 

 was involved. 



More is known concerning the distribution of Phyt. phaseoli, the oldest 

 recognized pathogene of the group, than for the other pathogenes. It is 

 of widespread occurrence in the United States and Canada, and, being 

 a seed-borne disease, probably is to be found in most bean-growing 

 countries. Delacroix (1899) reported the disease from France shortly 

 after Smith (1898) first described it as occurring in America. Little has 

 been said, however, concerning the presence of this pathogene in France 

 since Delacroix's report; and the writer was unable to find any bacterial 

 disease in the bean fields in Normandy and those about Paris during 

 the summers of 1924 and 1927. Welles (1922) reported the disease in 

 the Philippines, and Picado (1924) reported a yellow bacterium, which 

 probably was Phyt. phaseoli, causing a disease of beans in Costa Rica. 

 The pathogene was isolated by the writer from leaves and pods collected 

 in Bermuda in 1922, and from diseased pods collected in Switzerland in 

 1927. 



Phytomonas flaccumfaciens, a less generally recognized pathogene, is 



