72 Walter H. Burkholder 



Infected leaves of beans have been received from Bermuda, and also from 

 New Jersey, with small spots, reddish brown in appearance and some- 

 what raised above the surface of healthy tissue (Plate II). Pure cultures 

 of Phyt. phaseoli only were isolated from such lesions; nevertheless, Phyt. 

 vignae var. leguminophila also produces this type of lesion on bean leaves, 

 and so it can scarcely be considered a good diagnostic character. 



Phyt. flaccumfaciens, as a rule, wilts the entire leaf or leaflet of the 

 bean, but in some instances it has been known to wilt only a part of the leaf, 

 as in figure 5, which shows a rather large necrotic spot. A similar con- 

 dition may be produced by Phyt. phaseoli, if the necrotic area is of endog- 

 enous origin. 



On the pod, Phyt. viridiflava and Phyt. vignae var. leguminophila pro- 

 duce spots which from the beginning of their formation are brownish 

 and often dry and necrotic. The other bacteria produce spots which are 

 at first deep green and water-soaked in appearance. The water-soaked 

 condition of the lesion may persist, or under certain circumstances the 

 spots may dry down to reddish sunken areas. Over the pod spots pro- 

 duced by Phyt. phaseoli a yellowish crustation may sometimes be observed, 

 while a silvery crustation may be produced by Phyt. medicaginis var. 

 phaseolicola. This crustation is very delicate and is readily washed off 

 by rains, and therefore it is of very little use in differentiating the two 

 diseases. Phyt. flaccumfaciens, as has been pointed out, produces on the 

 green pod only water-soaked lesions along the suture, which are of endog- 

 enous origin. This symptom, however, can be duplicated by Phyt. 

 phaseoli, Phyt. phaseoli var. fuscans, and Phyt. medicaginis var. phaseo- 

 licola, and consequently it is not a character to be used without dis- 

 crimination. 



On the stem, Phyt. phaseoli produces reddish-colored lesions which 

 extend longitudinally with the stem. A stem girdling at the nodes also 

 is produced, and probably in the majority of cases this arises from an 

 infected xylem. Phyt. flaccumfaciens produces only the stem girdle. 

 A very striking peculiarity of Phyt. medicaginis var. phaseolicola is the 

 formation of the bacterial ooze, or exudate, on the stem lesions (figure 10). 

 No other bacterial disease of the bean has been observed to do this, and 

 therefore this symptom should be looked for in endeavoring to determine 

 the disease under observation. When Phyt. viridiflava is inoculated 

 into the stem of a growing bean plant, gall formation, as a rule, occurs. 

 This differentiates the lesion from those due to Phyt. vignae var. 

 leguminophila. 



When a systemic infection occurs in a plant, and a wilt results with 

 no definite stem, leaf, or pod lesions, the indications are that the invasive 

 organism is Phyt. flaccumfaciens. This pathogene is almost an obligative 

 vascular parasite, and when it is found in other tissues, as in the pod 

 lesion along the suture, it appears to be more of an overflow from the 



