52 Walter H. Burkholder 



isolated from these lesions, and also was found to be pathogenic to P. 

 vulgaris. This strain of the organism, which differed but slightly from 

 that from New Jersey, is referred to in this memoir as the " Q strain." 



For use in further study, for inoculation purposes and to determine the 

 cultural characteristics, the two strains of the pathogene were reisolated 

 from artificially inoculated bean plants showing the disease, and were 

 transferred from dilution culture plates. 



INOCULATION EXPERIMENTS 



On the bean 



This disease has not been studied in the field under natural conditions. 

 What is known concerning it has been learned by examination of plants 

 artificially inoculated, and usually under greenhouse conditions. The 

 variety of bean used in the majority of cases was Wells' Red Kidney, a 

 variety which proved to be highly susceptible to the pathogene. 



When the organism is introduced into the stem of a bean seedling or a 

 young plant, the disease appears within approximately four days. This 

 is an incubation period which does not differ greatly from those of several 

 of the other bean pathogenes. The mode of attack, however, differs some- 

 what from that of the other pathogenes with the exception of Phylomonas 

 viridijiava. The organism here considered is not a vascular parasite, as 

 is Phyt. flaccumfaciens, nor a facultative vascular parasite, as are Phyt. 

 phaseoli and Phyt. medicaginis var. phaseolicola. It does not show a 

 preference for the vascular system, although it sometimes follows the xylem 

 vessels. Consequently, when inoculated into the stem the bacteria seem 

 to invade all tissues. A sunken necrotic lesion ensues, but the epidermis 

 usually remains intact except at the point of inoculation. The plant parts 

 above this lesion die, due to their being cut off from the roots and not 

 necessarily due to the invasion of the organism in these parts. When a 

 seedling wilt results from an artificial inoculation, it is often accompanied 

 by a toppling-over of the plant at the point of inoculation. If not all of 

 the vascular tissue is affected at this point, the plant may recover some- 

 what. 



The disease never appears to be systemic without showing lesions along 

 the stem. Older plants that have become woody are more or less resistant 

 to the pathogene. In such cases the lesion may be on only one side of 

 the stem and the plant will continue to live. In all cases of infection on 

 the stem and the leaves, the organism works rapidly at first, but after a 

 few days the border of the lesion does not extend appreciably. Either the 

 invasive ability of the pathogene diminishes, or a certain resistance is 

 shown in the host. This mode of attack is entirely different from those of 

 Phyt. phaseoli, Phyt. phaseoli var. fuscans, Phyt. flaccumfaciens, and Phyt. 

 medicaginis var. phaseolicola, in all of which the persistency of the pathogene 

 remains fairly consistent. 



