Different species and symbiotic genotypes of field rhizobia can nodulate Phaseolus vulgaris in Tunisian soils

• Published in: FEMS microbiology ecology Vol. 41; no. 1; pp. 77 - 84
• Main Authors: Mhamdi, Ridha, Laguerre, Gisèle, Aouani, Mohamed Elarbi, Mars, Mohamed, Amarger, Noëlle
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2002
• Subjects: Phaseolus vulgaris; Rhizobium; Soil population; Soil population; Phaseolus vulgaris; Rhizobium
• ISSN: 0168-6496; 1574-6941
• DOI: 10.1016/S0168-6496(02)00264-7

A collection of 160 isolates of rhizobia nodulating
Phaseolus vulgaris in three geographical regions in Tunisia was characterized by restriction fragment length polymorphism analysis of polymerase chain reaction (PCR)-amplified 16S rDNA,
nifH and
nodC genes. Nine groups of rhizobia were delineated:
Rhizobium gallicum biovar (bv.)
gallicum,
Rhizobium leguminosarum bv.
phaseoli and bv.
viciae,
Rhizobium etli bv.
phaseoli,
Rhizobium giardinii bv.
giardinii, and four groups related to species of the genus
Sinorhizobium,
Sinorhizobium meliloti,
Sinorhizobium medicae and
Sinorhizobium fredii. The most abundant rhizobial species were
R. gallicum,
R. etli, and
R. leguminosarum encompassing 29–20% of the isolates each. Among the isolates assigned to
R. leguminosarum, two-thirds were ineffective in nitrogen fixation with
P. vulgaris and harbored a symbiotic gene typical of the biovar
viciae. The
S. fredii-like isolates did not nodulate soybean plants but formed numerous effective nodules on
P. vulgaris. Comparison of
nodC gene sequences showed that their symbiotic genotype was not related to that of
S. fredii, but to that of the
S. fredii-like reference strain GR-06, which was isolated from a bean plant grown in a Spanish soil. An additional genotype including 16% of isolates was found to be closely related to species of the genus
Agrobacterium. However, when re-examined, these isolates did not nodulate their original host.