The Bacterial Diseases of the Bean 69 



spots that developed on the inoculated pods were identical with those 

 produced by the Swiss strain, and the host range was similar. Pods of 

 all the species listed in cross inoculations with Phyt. viridiflava were used 

 in inoculation experiments with the English strain, with the exception of 

 Vicia faba and Pueraria hirsuta. These species did not set pods under 

 the conditions maintained in the greenhouse. 



In conducting inoculation experiments on pods of various species, a 

 further peculiarity of the organism and its relation to the host was observed. 

 When very young pods were used in the experiments, no infection was 

 obtained; but extensive infection occurred on maturing pods. When such 

 pathogenes as Phyt. phaseoli and Phyt. medicaginis var. phaseolicola are 

 used in inoculation experiments, almost the reverse of this is true, and it 

 is the case also with the fungous pathogenes of the bean. The susceptible 

 stage in the pod cannot be coupled with a dying of the tissue, since the 

 pod is susceptible for a considerable time before it shows signs of ripening 

 and while it is still in a green and apparently healthy condition. The 

 very young, rapidly growing pods, however, are resistant to the pathogene. 

 This phenomenon is demonstrated readily on such species as Phaseolus 

 coccineus and Vigna sinensis. It probably is found also with other species, 

 but it was with these two legumes that repeated inoculations and observa- 

 tions were made on young and on maturing pods. 



This host relationship probably is tied up with the low virulence of the 

 pathogene, and a somewhat similar case might be cited here. It has been 

 observed with Phyt. phaseoli and Phyt. vignae var. leguminophila that when 

 grown for some time in pure culture they lose their ability to infect the 

 stem of young plants, to produce either a vascular infection or a definite 

 lesion, as is the custom with each organism. Nevertheless, they still 

 retain their ability to infect bean pods. Experiments have never been 

 conducted, however, to determine their relative invasive ability on the pods 

 in various stages of maturity. 



DIFFERENTIATION OF THE BACTERIAL DISEASES OF THE BEAN 



The differentiation of the various bacterial diseases of the bean is of no 

 consequence to the average grower. The injuries caused by each disease 

 are somewhat similar in appearance, and the sum total is of considerable 

 economic importance. That much the grower appreciates, and a simple 

 method with which to combat these diseases is all that he asks. For the 

 plant pathologist, however, the ability to separate the diseases may be 

 of considerable importance. Aside from the investigation of the diseases 

 with a view to their control, the desirability of determining their distribu- 

 tion and the severity of their epiphytotics in various localities is well 

 understood. In endeavoring to distinguish the various diseases, the 

 determination of the etiological agent is always the final issue. Neverthe- 

 less, with these diseases the isolation of the bacteria and their identification 



