The Bacterial Diseases of the Bean 15 



ness of the pod, and certain environmental factors, no doubt contribute in 

 producing the differences in size and shape of the spots. All lesions are 

 at first water-soaked and dark green in color, but later the tissues may 

 become dry, sunken, and brick red. The process of drying begins at the 

 outer edge of the spot and extends inward, and it is not uncommon to find 

 a green, water-soaked lesion with a reddish, dry border. In many cases 

 a yellowish crustation, due to the bacteria oozing out and drying over the 

 lesion, covers the spot. 



When the bacteria enter the pod by the vascular system, they may produce 

 a long, irregular lesion along the suture (Plate IV, B). In other respects, 

 however, the lesions so produced resemble those described above which 

 arise from an external infection. 



On the seeds 



On white seeds, Phyt. phaseoli produces yellow spots of various sizes. 

 When an entire seed is involved, it may be wrinkled and yellow, and appear 

 as if it had been varnished. On colored seeds, small lesions are impossible 

 of detection, and larger ones cannot be distinguished from anthracnose 

 spots or abnormalities due to frost injury. Likewise, when immature 

 seeds are harvested they may show a slight wrinkling and discoloration 

 which at times could be mistaken for a bacterial infection. 



If the bacteria enter the seed through the vascular system, and infection 

 is light, they may produce only a yellow spot at the hilum, but in more 

 severe cases they spread out underneath the seed coat. Seed slightly 

 infected, either at the hilum or on the side, may escape detection during 

 picking in the seed house and be used the following year for planting. 



INOCULATION EXPERIMENTS 



On the bean 



Many of the symptoms just described have been reproduced on plants 

 in the greenhouse by artificial inoculation, especially the symptoms con- 

 nected with systemically infected plants. Red Kidney was the variety 

 used, and the temperature maintained was approximately 80° F. More 

 success in producing a vascular infection resulted from employing recently 

 isolated strains of the pathogene than with strains that had been in 

 culture for a year or more. Plants that were inoculated by pricking at the 

 cotyledon node and were then placed in a temperature of G5° F. did not 

 wilt as did those shown in Plate V, D and E, which were at 80° F. The 

 plants in the lower temperatures, however, developed typical leaf spots 

 on the lower leaves, and the bacteria in such lesions could be traced down 

 the xylem vessels to the point of inoculation on the stem. When plants 

 were inoculated through injuries, positive results were obtained in 100 

 per cent of the cases. When plants were sprayed with a water suspension 



