The Bacterial Diseases of the Bean 9 



in accordance with the classification which the various writers prefer: 

 Pseuclomonas (Migula), Bacterium (Lehman and Neuman, and E. F. 

 Smith), and Phytomonas (Bergey). In this memoir the Bergey classifica- 

 tion is adopted. 



For approximately twenty-five years after the discovery of Phytomonas 

 phaseoli, all references to a bacterial disease of beans assumed this organism 

 to be the etiological agent. Possibly in the great majority of the cases this 

 assumption was true, and the other bacteria pathogenic to this host are, 

 no doubt, of recent appearance. One reason for believing this, is the fact 

 that only in recent years in the United States have the bacterial blights 

 been so severe. It seems inconceivable that Phyt. flaccumfaciens or Phyt. 

 medicaginis var. phaseolicola, two organisms which are much more destruc- 

 tive at times than Phyt. phaseoli, would have been overlooked if they 

 were present on the bean, or that their virulence should have increased in 

 later years. Furthermore, these various pathogenes are not limited to 

 Phaseolus vulgaris, and it is entirely possible that they appeared originally 

 on other species and that their appearance on the bean is of but recent 

 occurrence. Pathogenic on a wild species or slightly pathogenic on some 

 cultivated host, they very easily could have been overlooked. After they 

 once got a foothold on the bean plant, and especially the seed stock, they 

 spread rapidly over the country. 



Since Phyt. phaseoli is the oldest and the best-known species of the 

 bacteria attacking the bean, it is the one with which all the others are 

 compared. For this reason this pathogene and the disease which it 

 produces are treated first. 



LIFE HISTORY 



In order to recognize and understand certain symptoms of the disease 

 caused by Phytomonas phaseoli and to differentiate them from the symp- 

 toms of the other bacterial diseases of the bean, a knowledge of certain 

 phases of the life history of the pathogene is helpful. The term life history 

 is used here in a broad sense, to designate not only the methods of over- 

 wintering of the organism, and the methods of infection, but also the tissue 

 of the plant that is attacked and the peculiar invasive ability of the 

 organism in the host. While these features are stressed in the following 

 sections, what is known of the entire life history of the pathogene is also 

 reported. 



One of the most important stages in the life history of an organism, from 

 the standpoint of primary infection and of control, is the stage in which it 

 passes the winter. The usual way in which Phyt. phaseoli survives the 

 cold months is in a dry condition in or on the bean seed. Here it is in a 

 highly resistant state, and under laboratory conditions at Ithaca, New 

 York, it has been known to remain viable for a period of three years. 

 Rapp (1919), in Oklahoma, is of the opinion that the pathogene in this 

 state will die within a year's time, and Sackett (1926), in Colorado, reports 



