Abstract
The results on the effect of pH on the growth of rhizobia observed in the yeast-water asparagine mannitol solution are summarized as follows : Optimum pH : Slightly acid reaction (pH 6〜7) is generally suitable for most of rhizobia, although lower pH range (pH 5.5〜6.5) is more favourable for some strains, while neutral or alkaline reaction (pH 7〜7.5) is better for the growth of alfalfa, soybean (B), and cowpea (F) bacteria. Critical pH : According to the critical pH in the acid side, rhizobia are divided into three groups. Group I. Acid sensitive (Critical pH 5.5〜6.0). ……Strains from alfalfa group, soybean (B), cowpea (F, G) Group II. Intermediate (Critical pH 4.9>>3.7) This group includes many strains from various inoculation groups and it may be subdivided, though not so clearly. Strains from genge, Robinia and Vicia (nipponia) are more acid-tolerant and those from lupine and soybean (A) are less than others. Among fast-growers, pea an clover bacteria seem to be more acid-sensitive than bean bacteria. Group III. Acid-tolerant (critical pH 3.3>). ……cowpea (E) Considered from each inoculation group or plant, this result seems also to suggest the possibility of subgrouping of the bacterial strains in alfalfa-, soybean-, and cowpea-group, and Sesbania, respectively.
