Abstract:
Pigeonpea (Cajanus cajan (L.) Millsp.) is an important grain legume, which, like several
other legumes, depends on the process of biological nitrogen fixation for its nitrogen (N2
) requirement
by forming a symbiotic association with rhizobia. Compared to other tropical legumes, however,
the productivity of pigeonpea in South Africa is low, despite the extensive interests in developing it
for wider markets. To assist this process, the objectives of the current study were to (i) characterize
putative indigenous rhizobial strains that were previously derived from local soils with no previous
history of legume cultivation and (ii) confirm their nodulation abilities on a local landrace and a
genetically improved (exotic) genotype of pigeonpea. DNA-based analyses using the 16S rRNA
and recA genes showed that the strains predominantly represented Rhizobium and Bradyrhizobium,
although we also recovered Phyllobacterium and Paraburkholderia. These rhizobia nodulated both the
local landrace and the improved pigeonpea genotype that were included for comparative purposes.
In many cases, rhizobia performed similarly on the two genotypes, although the locally sourced
landrace mostly performed better in terms of nodulation and plant biomass. While the current
study generated vital information regarding the diversity of indigenous rhizobia associating with
pigeonpea, further screening (including field inoculation trials) would be necessary to identify
possible elite nitrogen-fixing rhizobial strains for development as inoculants to enhance South African
pigeonpea production.
