This paper deals with six strains of
Agrobacterium tumefaciens, viz., two laboratory stock strains (S
1, At
2) and four strains (I, M, S
2 and S
3) which were isolated recently by the present author from crown galls on
Sedum and
Rosa. On these six strains, studies were made on their biochemical, tumor inducing and serological characteristics. Four strains (S
1, At
2, I and M) were not fermentative on simple sugars, while the remainning two (S
2, S
3) were markedly fermentative. When inoculated on
Sedum alboroseum, three (S
1, At
2, I) of the non-fermentative strains showed an excellent ability of gall formation. These three strains were found to share most of their antigens in immune diffusion agar, so that they were considered to be antigenically homogeneous. The fermentative strains (S
2, S
3) and one (M) of the non-fermentative ones showed only a limited degree of gall formation and serological behaviors distinguishable from the former, tumor-inducing group. According to Bergey, the key to the classification of plant pathogens belonging to the genus
Agrobacterium lies in nitrate reduction and indole reaction. In all of the six strains, the reaction for nitrate reduction was positive, but the indole reaction was shown to be negative altogether. In this respect, all the strains isolated must be assigned, according to Bergey, to the species
gypsophilae rather than
tumefaciens in the genus
Agrobcaterium. However, some contradiction has been encountered between the Bergey's criterion of
gypsophilae and the observation of the present pathogens in question. For the present, it seems that there is much to be improved in the classification of individual species in
Agrobacterium. As one of the reliable characteristics, the immunochemical properties may be supplemented for this purpose because of a closer connection with the infectivity of these pathogenic microbes. The experiments were made with caution along this line, and the availability of the results was discussed.
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