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Effect of Soil Temperature on Rhizobium japonicum Serogroup Distribution in Soybean Nodules¹

Studies were conducted to determine if temperature, as suggested in a previous study, influenced the distribution of serogroups in nodules of soybeans grown in these same soils. The soybean variety ‘Lee’ was grown at constant soil temperatures of 10, 20 and 30 C and 15, 20, 25 and 30 C, respectively, in two greenhouse experiments. Codorus silt loam containing an established population of Rhizobium japonicnm was taken from sites of a previous date of planting study and incubated for one week at the desired temperature before uninoculated seed was planted.

Plant growth characteristics, nodulation and distribution of R. japonicum serogroups in the nodules were recorded. Plant development and nodulation generally were favored by increasing temperatures with 30 C the most favorable temperature for all characteristics except nodule size.

Serological distribution of R. japonicum in the nodules was influenced by soil temperature. Serogroups which were infrequently recovered at the lower temperatures became dominant at 30 C whereas serogroups forming the majority of nodules at 10 or 15 C formed fewer nodules at 30 C. Leaf chlorosis which is induced by R. japonicum serogroup 94 was evident only at 30 C where its incidence in the nodules was highest.

Key Words: Glycine max (L.) Merrill • Competition • Ecology

² Microbiologist and Research Technician, Plant Science Research Division, ARS, USDA, Beltsville, Md. 20705.

Received for publication February 28, 1972.