Genotypic Diversity among Strains of Bradyrhizobium japonicum Belonging to Serogroup 110

Abstract

Thirty-three strains of Bradyrhizobium japonicum within serogroup 110 were examined for genotypic diversity by using DNA-DNA hybridization analyses. The analysis of the DNA from 15 hydrogen-uptakenegative strains with the bradyrhizobial uptake hydrogenase probe pHU52 showed variation in degree of homology and restriction fragment length polymorphism of EcoRI-restricted DNA. Clustering analysis of the 33 strains on the basis of DNA-DNA hybridization analysis with four restriction enzymes and with the bradyrhizobial nodulation locus, pRJUT10, as probe indicated the existence of four groups of strains, which were less than 70%o similar. Restriction digestion of genomic DNA with BamHI and DNA-DNA hybridization with pRJUT10 permitted classification of each of the strains according to a specific fingerprint pattern.

Host-Controlled Restriction of Nodulation by Bradyrhizobium japonicum Strains in Serogroup 110

“…The majority of group 1 strains, 80%, were restricted for nodulation on PI 417566, whereas 64% of the group 2 strains failed to nodulate PI 417566. Our division of the 110 serogroup strains into specific groups by MLEE analysis is similar to what has been reported by others using nod gene hybridization analysis (27). However, the serogroup strains were more tightly clustered by MLEE analysis (divergence in similarity was at 0.85%) than they were by hybridization studies, in which strains were found to diverge at 65%.…”

“…These include a generalized resistance of the host to further invasion by rhizobia, the blockage of nodule initiation sites (2), and saturation of the nodulation capacity of the host (1). Since USDA 110 has the ability to curl root hairs, initiate infection thread formation, and induce nodule primordia on PI 417566 (22), our results suggest that host-strain incompatibility for nodulation and nodulation blocking is most likely governed by an autoregulatory feedback mechanism which operates after the initiation of the infection process (16,27).…”

“…However, the serogroup strains were more tightly clustered by MLEE analysis (divergence in similarity was at 0.85%) than they were by hybridization studies, in which strains were found to diverge at 65%. Interestingly, the two group 1a serogroup 110 isolates that were not restricted for nodulation on the PI genotype, USDA 452 (WI 3278) and USDA 456 (WI 3054), also fall into a distinctive group on the basis of nod probe hybridization analysis (27). Isolation of a USDA 110 mutant with the ability to nodulate PI 417566.…”

Diversity among Field Populations of Bradyrhizobium japonicum in Poland

“…plants. Results from several studies in the United States and abroad have indicated that there is considerable physiological (15,21,23,24), symbiotic (19), serological (5,7,27,32,40), and genetic (10,14,19,34,37) diversity among strains and serogroups of B. japonicum. Soybean nodulation in production fields often occurs by competitive, yet ineffective bradyrhizobia.…”