Influence of Inoculum Size on Rhizobium japonicum Serogroup Distribution Frequency in Soybean Nodules
1973
Kapusta, George | Rouwenhorst, D. L.
Investigations were conducted in 1969 and 1970 to determine the influence of ultra-high inoculation rates of a single Rhizobium japonicum strain on recovery from soybean (Glycine max (L.) Merr.) nodules. Biological seed yield, nodule mass, seed oil, and protein also were studied. Bacterial suspensions containing up to 1.2 × 10¹² rhizobia per cm of row were banded in contact with the seed during planting. A rapid agglutination test was used to distinguish R. japonicum serogroups in homogenized nodule suspensions. Strains 138 and 126 were used as the inoculum in 1969 and 1970, respectively. Control plot rhizosphere R. japonicum population was between 30,000 and 300,000 per g of oven-dried soil. The predominant naturalized serogroups in these plots were 123 and c-1(138) in 1969 and 1970, respectively, despite a distance of only 300 m between test areas. Strain 138 recovery percentage in 1969 increased from 18% in the uninoculated plots to 60% in plots receiving 15 billion rhizobia per cm of row. Similar significant shifts occurred in 1970. The data indicate that it is possible to evoke shifts with at least two serogroups. If superior strains are developed in the future, this technique would be one way to establish them rapidly. Nodulation, plant growth characteristics, seed yield, and oil and protein content were not influenced by the inoculum rates with one exception. Biological yield was significantly increased in ]970 at the highest inoculum rate. The reason for this observation is not readily apparent.
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