The Bacterial Diseases of the Bean 39 



phaseoli. The two organisms are alike, however, in the tissue which they 

 attack. Each shows a preference for the vascular tissue, and uses the 

 xylein vessels as a means of spreading throughout the plant. They can, 

 on the other hand, attack the other tissues of the plant with great vigor, 

 although they do not spread so rapidly in these. 



One point in the life history of the organism of which little is known is 

 its ability to overwinter in the soil. In the greenhouse it is known to live 

 for several months in garden loam, but no carefully conducted experiments 

 have been carried on in the open. From observations in the fields of 

 New York, it is evident that clean seed, such as is brought in from California, 

 produces, as a rule, healthy crops of beans. Since the crop rotation in 

 the bean section, however, is seldom less than three years, it would be 

 necessary for the pathogene to remain viable in the soil for that length 

 of time in order for this phase of its life history to be of any economic 

 importance. There is no indication that the organism possesses this ability. 



SYMPTOMS 



Stunting and wilt 

 It has been pointed out, in the discussion of the life history of Phytomonas 

 medicaginis var. phaseolicola, that this pathogene, while not obligatively a 

 vascular parasite like Phyt. flaccumfaciens, nevertheless does show a decided 

 tendency to invade the xylem vessels. The result of the infection of the 

 xylem tissue is, in most cases, a symptom complex, and should be regarded 

 as such rather than as isolated individual symptoms. The latter is the 

 case only when the infection is local. The symptoms arising from the 

 infection of the xylem are definite, and in certain respects are peculiar to 

 this disease. A seedling wilt, however, may result which is not peculiar 

 to this organism and which cannot be distinguished from such a wilt 

 induced by other bacterial pathogenes. In inoculation experiments this 

 wilt takes place in about four days, but it is not of frequent occurrence in 

 the field. Possibly the reason for this is that the seeds which are planted 

 have been graded in a seed house, where the severely infected seed are 

 removed and only the lightly infected ones remain; consequently, the 

 bacteria are not present in sufficient quantity to enable them to reach the 

 seedling from the cotyledon and cause a wilt at this early stage of develop- 

 ment. Young plants with infected xylems, however, will soon show certain 

 definite symptoms of the disease. They are stunted in growth, and as the 

 pathogene progresses upward in the stem the lower leaves are invaded and 

 soon wilt. The leaf petiole in this case remains upright, while the leaflets 

 droop downward, become dry and brown, and persist until they are 

 destroyed by wind or rains. As the disease progresses upward, the 

 remaining leaves, the young shoots, and the immature pods succumb. 

 The upper leaves and shoots of an infected plant are stunted in their 

 development, and become chlorotic before they finally are killed. From 

 this it appears that the pathogene in the xylem vessels produces a toxin 



