14 Walter H. Burkholder 



border, and surrounding this there is often a narrow pale green zone. One 

 or more of these spots may increase in size and involve a large part of the 

 entire leaflet. After a heavy rain or windstorm, such leaves have a very 

 ragged and torn appearance. These typical lesions are, as a rule, due to 

 external infection, but at times they may develop from the bacteria 

 rising from the vascular system. 



Several other types of leaf spots of beans have been observed and have 

 been described before. One of these occurs only on young leaves. In 

 this type the leaf is covered with small, angular spots which are at first 

 water-soaked and dark green in appearance, but which later dry out and 

 become brown. The necrotic tissue in the lesions is in the islets between 

 the veins, and infection of the vascular bundles does not appear to have 

 taken place. 



On several occasions an anomalous type of lesion on the bean leaf has 

 been observed. The varieties affected were the Red Kidney and an 

 unknown green-pod variety. The spots in each case varied somewhat in 

 size, but were not large, and were slightly raised above the healthy surface 

 of the leaf (Plate II). In color they were a red-brown, and not unlike 

 the leaf spot of lima beans due to Phyt. vignae. Isolations were made 

 from a number of such lesions, and in all cases the pathogene appeared 

 to be Phyt. phaseoli. No careful study of the cultures was made, however, 

 outside of determining their pathogenicity on the common bean. Whether 

 or not they were a distinct variety or race of Phyt. phaseoli is not known. 



On the stem 



Phijt. phaseoli produces water-soaked lesions on the stems of bean 

 seedlings, as may be observed where diseased seeds have been planted. 

 As these lesions grow older, they lose their water -soaked appearance, dry 

 down, and become reddish brown in color. On older plants the water- 

 soaked condition seldom is evident. Stem lesions usually are in the shape 

 of streaks and are always longitudinal with the stem. 



A second type of lesion found on the stem of the bean and due to this 

 organism is the stem girdle. This injury sometimes causes considerable 

 damage to the crop. The lesion is produced at the cotyledon, or more 

 frequently at the first leaf node, or less frequently higher up on the plant. 

 In these cases the vascular system is infected and the bacteria come to 

 the surface in the leaf traces, resulting in the girdle. The color of these 

 lesions is reddish brown, as is that of the streaks on the stem. Plants 

 affected with the stem girdle become weakened at the infected node and 

 are easily toppled over during a windstorm. 



On the pods 



Several types of lesions occur on bean pods, as may be seen in Plates II 

 and IV and in figure 11 (page 46). The number of infections, the tender- 



