The technique of enzyme-linked immunosorbent assay (ELISA) was used for serological identification of peanut Rhizobium strains both in cell suspension of pure culture and in single root nodules of groundnut (Arachis hypogaea) plants. Antisera of three peanut Rhizobium strains were tested against eight different Rhizobium isolates. Three serogroups identified by agglutination and immunodiffusion tests were confirmed by ELISA. In this experiment ELISA was more sensitive by four to six orders of magnitude than the agglutination and immunodiffusion tests and enabled the detection of Rhizobium antigens in cell suspensions of 10(4)-10(5) cells per millilitre. The reactions of culture and nodule antigens were identical for all strains investigated. ELISA enabled the precise typing of rhizobial isolates in single small root nodules. The minimum fresh weight of nodule tissue necessary to perform the ELISA test was 0.4 mg crushed in 1 ml of phosphate-buffered saline (PBS). ELISA was also successfully used for strain identification in mixed inoculated plants. One of the strains in each pair formed most of the nodules examined.

Three strains of Bradyrhizobium, 280A, 2209A and 32H1, that nodulated peanuts (Arachis hypogaea L.), were tested for their ability to grow and survive at elevated temperatures of up to 42°C in laboratory culture. Strain 32H1 was unable to grow at 37°C and was more sensitive to elevated temperatures than the other two strains. All three produced heat-shock proteins of molecular weights 17 kDa and 18 kDa. Two greenhouse experiments were conducted to determine the effect of high root temperature on nodulation, growth and nitrogen fixation of peanut. Two peanut varieties (Virginia cv NC7 and Spanish cv Pronto) were inoculated and exposed to root temperatures of 30 °, 37 ° and 40°C. Nodulation and nitrogen fixation were strongly affected by root temperature but there was no variety x temperature interaction. At a constant 40°C root temperature no nodules were formed. Nodules were formed when roots were exposed to this temperature with diurnal cycling but no nitrogen fixation occurred. Highest plant dry weight, shoot nitrogen content and total nitrogen were observed at a constant root temperature of 30°C. Increasing root temperature to 37°C reduced average nitrogen content by 37% and total nitrogen by 49% but did not reduce nodulation, The symbiotic performance of the strains corresponded to their abilities to grow and survive at high temperature in culture.

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The direct double-antibody enzymelinked immunosorbent assay system was used in the detection and measurement of seed lectins from peanut (Arachis hypogaea L.) and soybean (Glycine max L.) plants (PSL and SBL, respectively) that had been inoculated with their respective rhizobia. Concentrations of PSL dropped to undetectable levels in peanut roots at 9 d and stems and leaves at 27 d after planting; SBL could no longer be detected in soybean roots at 9 d and in stems and leaves at 12 d. A lectin antigenically similar to PSL was first detected in root nodules of peanuts at 21 d reaching a maximum of 8 μg/g at 29 d then decreasing to 2.5 μg/g at 60 d. There was no evidence of a corresponding lectin in soybean nodules.Sugar haemagglutination inhibition tests with neuraminidase-treated human blood cells established that PSL and the peanut nodule lectin were both galactose/lactose-specific. Further tests with rabbit blood cells demonstrated a second mannosespecific lectin in peanut nodule extracts that was not detected in root extracts of four-week-old inoculated plants or six-week-old uninoculated plants, although six-week-old root extracts from inoculated plants showed weak lectin activity. The root extracts from both nodulated and uninoculated plants contained another peanut lectin that agglutinated rabbit but not human blood cells. Haemagglutination by this lectin was, however, not inhibited by simple sugars but a glycoprotein, asialothyroglobulin, was effective in this respect.