Antigenic and symbiotic characterization of indigenous Rhizobium leguminosarum bv. tripolii recovered from root nodules of Trifolium pratense L. sown into subterranean clover pasture soils

Abstract

Isolates of Rhizobium leguminosarum bv. trifolii were recovered from root nodules of red clover ( Trifolium pratense L.) cullivar Florie sown umnoculated into two acidic Oregon soils of the Whobrey and Abiqua series which had been in subclover ( Trifolium subterraneum L.) pasture for 30–40 yr. Gel-immune-diffusion studies showed that none of the Whobrey isolates were antigenically identical to serogroups WS 1-01 or WS 2-01, previously shown to dominate nodules of field-grown 7'. subterraneum L. in this soil. Twenty-seven and 50% of the Whobrey isolates were placed into two previously unidentified serogroups. WR 26 and WR 27 respectively. Only two of the Abiqua isolates were antigenically identical to any of five serogroups, AS 6, AS 16, AS 17, AS 27 or AS 36, previously recovered from T. subterraneum L. growing in this soil; a previously unidentified serogroup, AR 21 constituted 50% of the isolates. An antigenic relationship between serogroups WR 27 and AS 16 was confirmed by whole-cell somatic tube agglutination, gel immune-diffusion and fluorescent antibody reactions. An incomplete antigenic relationship between serogroups WR 26 and AR 21 was also established. Immunofluorescence counts confirmed the presence of organisms antigenically related to four of the AS serogroups in samples of Whobrey soil recovered from the field. The population densities of some of the indigenous serogroups observed in Whobrey soil were significantly different ( P = 0.05) from each other. Only 5% of Whobrey isolates were ineffective on red clover, whereas 48% of the isolates were incapable of fixing N on subclover. With few exceptions, the Abiqua red clover isolates were ineffective or suboptimally effective on either host. Most isolates which displayed the same N-fixing trait on red clover expressed at least two effectiveness traits when evaluated on subclover.