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Genetic diversity of rhizobia nodulating the mimosoid legumes
Author
Pang, Kia Keng
Supervisor
Tham, Foong Yee
Abstract
A total of 127 mimosoid plants belonging to the Acacieae, Ingeae, Mimoseae and Parkieae from six different locations in Singapore were examined for nodulation. All plants examined nodulated except for Adenanthera bicolor, Adenanthera pavonina and Parkia speciosa. Nodules varied in size and gross morphology. Nodule morphology was not determined by rhizobia species that infected the plant. A total of 45 isolates were recovered from nodules of 12 mimosoid species. Five different phenotypes on Yeast Mannitol Agar were observed. These included fast-, slow- and moderate-growing isolates. All isolates were Gram-negative. Of 20 randomly selected isolates, 40% had intrinsic antibiotic resistance (IAR) to 8 antibiotics ampicillin, chroamphenical, gentamycin, kanamycin, neomycin, penicillin G, streptomycin and tetracycline. Of the remaining susceptible to at least 5 of the antibiotics, all were resistant to penicillin G, ampicillin and chloramphenical. 7 IAR groups were detected. Restriction digests of the IGS-PCR product of 25 isolates generated 6 PCR-RFLP groups. There was correlation between IAR and PCR-RFLP groupings. DNA sequencing of IGS-PCR products from 31 isolates was carried out and used in a BLAST search for matches in GenBank. Sequences matched to 14 known bacterial strains, 1 to an uncultured bacteria clone, and 1 had no significant similarity to any known sequences. The isolates from mimosoid legumes had high percent identity to Bradyrhizobium, Mesorhizobium, and Rhizobium sp. (α-proteobacteria species), and to Burkholderia and Ralstonia (β-proteobacteria species). This study shows that mimosoid legumes in the tropics can be nodulated by both α-proteobacteria and β-proteobacteria with β-proteobacteria being the prevalent symbiont. Generally, there was high promiscuity and little host-rhizobial specificity with different bacteria species co-existing in a single species and, a single bacterial species infecting more than one host type.
Date Issued
2008
Call Number
QR82.R45 Pan
Date Submitted
2008