The Bacterial Diseases of the Bean 37 



Brief description 



Phytomonas flaccumfaciens is a short, non-spore-forming rod with rounded 

 ends, occurring singly or in pairs. The average size of the cells is 1.75 by 

 0.82/x. The organism is motile by means of a single polar flagellum. It 

 is Gram-positive, not acid-fast, and apparently a fairly strict aerobe. 

 Capsules have not been observed. 



On agar slants the growth is moderate, filiform, and pale yellow in color. 

 The consistency of the culture is often viscid; broth cultures are cloudy in 

 twenty-four hours; gelatin liquefaction, as a rule, is light; a soft curd is 

 formed in milk; litmus is reduced; acid is produced, but no gas, in dextrose, 

 saccharose, lactose, and maltose broth; starch is not hydrolyzed or but 

 slightly; nitrates are not reduced to nitrites; indol is not formed; hydrogen 

 sulfide is not produced; there is no growth in Uschinsky's, Fermi's, or 

 Cohn's solution; pathogenicity or virulence is not lost in culture. 



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

 and on many related species. 



HALO BLIGHT CAUSED BY PHYTOMONAS MEDICAGINIS VAR. PHASEOLI- 



COLA 1 



The bacterial disease of greatest economic importance in New York 

 is the one caused by the organism Phytomonas medicaginis var. phaseolicola. 

 This disease was first noticed in 1924, and, because of the severity of its 

 attack, suspicion immediately arose that it was distinct from the other 

 known bacterial diseases of beans. The rapidity with which the disease 

 spreads through a field, and the severity of the symptoms on the individual 

 plants, are still undiminished. 



In that section of New York where the Red Kidney bean is grown 

 extensively, this disease has been in the past few years a limiting factor to 

 production. It may be differentiated on this variety from the other 

 bacterial diseases almost alone by the severity of its attack, regardless 

 of the types of symptoms. On the other hand, the Pea bean, the Marrow, 

 and the Yellow Eye, of the dry-shell varieties, and the Refugee of the 

 green-pod types, are not so susceptible as the Red Kidney, although they 

 should never be considered resistant. 



The distribution of the disease, and the extent of its economic importance 

 outside New York, have never been carefully investigated. Apparently 

 it is of widespread occurrence. Miss Hedges (1928) has reported it from 

 Georgia and Montana, and she states that in those sections it causes 

 considerable losses to the crop. In 1927 the writer isolated the causal 

 organism, Phyt. medicaginis var. phaseolicola, from specimens collected in 

 Switzerland, showing that the disease it is not limited entirely to America. 

 It probably is of widespread distribution, but its general similarity to the 



1 In a recent publication (Phytopath. 20:140. 1930), Miss Hedges states that Phytomonas pueraria 

 is a synonym of Phyt. medicayinis var. phaseolicola. 



