Nov. IS, 1919 Bacterial Blight of Soybean 189 



VARIATIONS AMONG STRAINS 



As has already been suggested, a number of other strains of the blight 

 organism have been isolated and studied in comparison with strain A, 

 and during the progress of this work certain interesting variations have 

 been found to exist. 



The original isolation, strain E, was obtained from a leaf lesion in the 

 fall of 1 91 5, was studied in the greenhouse and culturally in the laboratory 

 during 191 6, and has been used in comparison with the type strain, A, 

 in all inoculation and culture work since that time. Its original patho- 

 genicity was proved ; but its virulence, which was never so great as that 

 of A, seems to be practically lost after three years. 



In culture, strains A and B behave very much alike, but with one 

 marked difference. It has been shown that strain A causes a consistent 

 browning of certain media, such as beef-peptone broth, beef-peptone 

 agar, and peptone solution plus certain sugars ; whereas strain E does not 

 cause this color change. Also, strain E, under favorable condition for 

 growth, develops, on potato agar, colonies and streak cultures showing a 

 decidedly wrinkled and convoluted surface. On the other hand, while 

 colonies and slope cultures of strain A, grown on potato agar, may develop 

 a more or less irregular surface also, ordinarily they appear much smoother 

 than those of E and do not make such an abundant growth. There is in 

 addition a slight color difference, strain A showing on potato agar a 

 browning tinge which is absent in E until the cultures are rather old. 



A number of isolations made during the seasons of 191 7 and 191 8 

 from leaf, petiole, and seed lesions correspond with strain A in color 

 and in the ability to brown peptone media. In general, colonies and 

 slope cultures of these isolations, on potato agar, compare more favor- 

 ably with strain E in surface irregularity, although there are smooth 

 types among them. These later strains have not been studied in detail, 

 but they have all proved to be pathogenic on soybean leaves and are 

 apparently the same as the type leaf strain. The writer also has in 

 reserve certain isolations made from stem and leaf which correspond 

 with the original strain E in grosser cultural characters and in the ap- 

 parent inability to cause browning of the peptone media. It is hoped 

 that the pathogenicity of these strains may be determined during the 

 coming season. One strain of this type, recently isolated from a leaf 

 which developed natural infection in the greenhouse, has produced 

 typical lesions on soybean seedlings. 



On beef-peptone agar no structural differences between colonies and 

 streaks of different strains appear. Here we find simply the difference 

 in ability to brown the medium. Plates 14 and 15 show the lack of 

 uniformity in the surface characteristics of colonies and slope cultures 

 of pure, authentic strains of the soybean blight organism. It will be 



