The Bacterial Diseases of the Bean 21 



and on the surface of the agar. A very slight browning takes place 

 along the stab. If hydrogen sulfide is produced, which is contrary to 

 other reports, there is only a slight production. 



Chromogenesis. The distinct yellow pigment appears to be produced on 

 all types of media. In liquid media, yellow rings and yellow sediments 

 are distinctly evident. The pigment is not water-soluble. 



Oxygen relations. From its behavior in fermentation tubes and in shake 

 agar cultures, the organism appears to be a rather strict aerobe. 



Longevity. In a dry condition, on or in the seed of its host plant, the 

 pathogene will remain viable for several years. In culture, however, the 

 life of the organism is comparatively short. Transfers should be made 

 at least once a month to prevent the strain from dying out. 



Virulence. It has been stated in literature that the organism does not 

 lose its pathogenicity or its virulence in pure culture. The reverse 

 statement also has been made. In working with a great many strains, 

 the writer has always been able to produce lesions on green pods no 

 matter how long the strain had been in culture. In the endeavor to 

 produce a seedling wilt or to cause a systemic infection of a bean plant, 

 success appears always to be certain with a recently isolated strain, but 

 negative results are often obtained with a strain that has been in culture 

 for a year or two. Possibly this accounts for the difficulty obtained 

 from time to time in producing an infection of the vascular system. 



Thermal death-point. A few thermal-death-point tests have been made 

 with this species, but with indefinite results. The thermal death-point 

 appears to be low, probably around 48° C. 



Brief description 



Phytomonas phaseoli is a medium-sized rod with rounded ends, occurring 

 singly or in pairs. The average length of the cells is 1.9ju- The organism 

 is motile by means of a single polar flagellum. It is Gram-negative, not 

 acid-fast, and apparently a fairly strict aerobe. Capsules have not been 

 observed. 



On agar slants the growth is good, filiform, and yellow in color. The 

 consistency of the culture is watery to butyrous; broth cultures are cloudy 

 in twenty-four hours; gelatin is liquefied; milk is peptonized without a 

 curd; there is no acid nor gas in dextrose, saccharose, lactose, or maltose 

 broth; starch is digested; nitrates are not reduced to nitrites; indol is not 

 formed; hydrogen sulfide is not produced or but slightly; there is no growth 

 in Fermi's or in Cohn's solution; growth in Uschinsky's solution is slight; 

 the thermal death-point is approximately 48° C. 



The organism is pathogenic on the common bean (Phaseolus vulgaris) 

 and on several closely related species. 



