Abstract
The mechanism of variation in nodule forming ability in some strains of Rhizobium Japonicium on host plants was studied in relation to soybean varieties. Two strains of Rhizobium Japonicium viz. TODAI No. 53 which, except on soybean var. NORIN No. 1 forms nodules on many soybean varieties with ease and strain TODAI No. 56 which forms nodules on many soybean varities including var. NORIN No. 1 were used in these experiments. (1) The inoculation tests were made using 14 soybean variteies. The results show that the strain TODAI No. 53 does not produced nodules on var. NORIN No. 1, var. ZIZUKA-IBARAKI No. 1 (one of the parent of var. NORIN No. 1) and on some other varieties genetically related to var. NORIN No. 1, but it produce nodules on other varieties, while the strain TODAI No. 56 produces nodules on all varities used in this tests. (2) The results of histological observation show that both strains of Rhizobium Japonicium produce the first infection cells in host roots of var. NORIN No. 1, but later growth of bacteria of these strains is different. The strain TODAI No. 53 does not multiply after producing the first infection cell while the strain TODAI No. 56 continuously grows in it and produces the nodules. (3) The cultural experiments of both strains of Rhizobium Japonicium were done using the rot extract-agar medium prepared from the roots of var. NORIN No. 1 and var. GOSHIYA, Strain TODAI No. 53 produces nodules on the var. GOSHIYA. The growth of both these strains is almostely same on the var. GOSHIYA's extract-agar medium and on the AO medium (RAGGIO: 1957), but their growth is different on the extract-agar medium of var. NORIN No. 1. The amount of growth of strain TODAI No. 53 on extract-agar medium of var. NORIN No. 1 containing 1, 200 mg/100 ml dry root powder was almost equal to the amount of growth of strain TODAI No. 56 on extract-agar medium containing 400 mg/100 ml dry root powder. (4) The amount of growth of both these strains was compared by growing them in different cultural mediums which were made by adding components of AO medium separately to the some concentration of extract-agar medium of var. NORIN No. 1 (dry root powder 400 mg/100 ml). The amount of growth of strain TODAI No. 53 on the culture medium containing all inorganic elements and phosphate element of AO medium was almost equal to that of strain TODAI No. 56 on the culture medium not containing the components of AO medium. The auther suggests that the phosphate requirement of strain TODAI No. 53 for its growth is much higher than that of strain TODAI No. 56 and the phosphate concentration in roots of soybean var. NORIN No. 1 and some other genetically related varities is lower than in other soybean varieties. Due to these facts Rhizobium Japonicium stain TODAI No. 53 is incapable of producing nodules on var. NORIN No. 1 and some other genetically related varieties.
