The Bacterial Diseases of the Bean 75 



yellow of Phytomonas phaseoli and the browning of the media due to 

 the action of Phyt. phaseoli var. fuscans. The yellow pigment of Phyt. 

 flaccumjaciens may be so faint at times as to be scarcely visible, as on 

 agars containing dextrose, and at other times or with other strains it 

 may be as deep a yellow as in Phyt. phaseoli. The yellowish cream color 

 of Phyt. viridiflava often is not observed. Older cultures show it better 

 than do young cultures, and the sugar broths (dextrose and saccharose) 

 bring out the color as a distinct orange, which may be confused with an 

 indicator if such is present in the medium. The water-soluble green 

 fluorescent pigment appearing on some media is a variable character, but 

 Phyt. vignae var. leguminophila and Phyt. viridiflava have always produced 

 this pigment on beef-extract agar (Bacto-peptone and Armour's beef 

 extract). Phyt. medicaginis var. phaseolicola, while belonging to the 

 green-fluorescent group, never produces the pigment on beef-extract agar. 

 On the whole, however, it appears safer to base differences on physiological 

 reactions in the media than on pictorial descriptions. 



In a previous article (Burkholder, 1930), the writer pointed out that 

 the genus Phytomonas is composed of at least three, and perhaps four, 

 rather distinct groups of bacteria. It is interesting to note that each of 

 the various bacterial pathogenes of the bean plant fall into one of the 

 three distinct groups. Phyt. phaseoli and its variety fuscans belong to 

 the Campestre group; Phyt. flaccumjaciens belongs to the Stewarti group, 

 which contains the large proportion of Gram-positive and non-motile 

 species; and the remaining organisms, Phyt. medicaginis var. phaseolicola, 

 Phyt. vignae var. leguminophila, and Phijt. viridiflava, are green-fluorescent 

 forms. While these green-fluorescent bacteria constitute a rather well- 

 defined group of pathogenes, the individual members within are not 

 clear-cut. Many of the pathogenes vary only slightly from the others, 

 both in pathogenicity and in cultural reaction. In other words, there 

 appear to be a great number of species, varieties, and forms, from which 

 one might assume that the bacteria are not very stable. A condition 

 exists here which is similar to that found in the genus Fusarium of the 

 fungi. A discussion of the variability of the group is scarcely pertinent 

 at this time, but it is interesting to note that the green-fluorescent bean 

 pathogenes illustrate the point rather well. Phyt. medicaginis var. phaseo- 

 licola and Phyt. vignae var. leguminophila might have been given specific 

 names, and no doubt would have been so treated by many investigators; 

 but they exhibit such a close relationship to Phyt. medicaginis and Phyt. 

 vignae, respectively, that it was considered best to show this in their 

 name. In discussing the variability of the group, it should be pointed 

 out also that the New York strain of Phyt. vignae var. leguminophila differs 

 slightly from the New Jersey strain, and the English strain of Phyt. viridi- 

 flava is not identical with the Swiss strain, when pathogenicity is con- 

 sidered. 



