The Bacterial Diseases of the Bean 



73 



xylem tissue. While Phyt. phaseoli, Phyt. medicaginis var. phaseolicola, 

 and to a less extent Phyt. phaseoli var. fuscans, prefer the xylem and 

 consequently also cause a wilt, these pathogenes are in no way limited 

 to this tissue. They may cause infection in almost any part of the plant. 

 On the other hand, Phyt. viridiflava, and to a less extent Phyt. vignae 

 var. leguminophila, appear to show no preference for the vascular tissue. 

 When they cause a wilt it is due to the invasion of most of the tissues of 

 the stem, including the vascular tissue, and wilting and death of the plant 

 parts above occur as a natural sequence. 



In summing up the information, one can only conclude that the best 

 and surest way to diagnose one of these bacterial diseases in the field 

 is to consider the sum total of all the symptoms displayed, and arrive at a 

 decision from them. Even then one cannot always be correct. In table 

 1, descriptions of the various characteristic symptoms of these diseases 

 have been brought together and arranged to facilitate diagnosis. 



TABLE 1. Major Symptoms Produced by Six Different Bacterial Pathogenes on 

 the Bean (Phaseolus vulgaris) 



Pathogene 



Phytomonas phi- 

 seoli 



Wilt 



Result of a vascular 

 invasion 



Stem lesions 



Leaf lesions 



Pod lesions 



Reddish lesions longitu- Definite necrotic lesions of Lesions at first water- 

 dinal with stem, also varying size with yellow- soaked, angular, anasto- 

 stem girdle | ish border, Several other mosing, drying into red- 



types of lesions dish sunken areas; lesions 



along suture of endoge- 

 nous origin 



Phyt. phaseoli var. 

 fuscans 



Same as with Phyt. 



Same as with Phyt. Same as with Phyt. pha- 

 phaseoli, but lesions seoli 

 are inclined to split 

 stem 



Same as with Phyt. pha- 

 seoli 



Phyt. flaccumfaci- 

 ens 



Result of a vascular in- 

 vasion. A major 

 symptom 



Stem girdle 



A part of the leaf, but; Along suture only, and of 

 more often the entire endogenous origin; le- 

 leaf, may wilt sions at first water-soaked 



and green 



Phyt. medicaginis 

 var. phaseolicola 



Result of a vascular Lesions longitudinal with Definite necrotic lesions Similar to those produced 

 stem; drops of bac-j with light-colored halo;: by Phyt. phaseoli; a sil- 

 lerial exudate some-, small angular spots; mo- 

 times appear saic and yellow symp- 

 toms due to systemic 

 infection 



very crustation some- 

 times appears over lesion 



Phyt. vignae var. 

 lejuminophila 



Necrotic lesions killing Sunken longitudinal le- Definite, 

 stem, resulting in sion which involves all rather small lesions; 

 wilting and death of stem tissue wilted parts above stem 



parts above lesions 



reddish brown, Brownish, dry lesions, nev- 

 er water-soaked ; some- 

 times a ring spot 



Phyt. viridiflava . 



Definite necrotic lesion Definite lesions involving 

 killing stem, result- all tissue; gall produc- 

 ing in wilting and, tion 

 death of parts above. 



(?) 



Reddish brown spots, never 

 water-soaked 



