BIOCHEMICAL CHARACTERIZATION AND PHYLOGENETIC DIVERSITY OF MESORHIZOBIUM/ MESORHIZOBIAL STRAINS NODULATING CHICKPEA
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Date
2018
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DIVISION OF MICROBIOLOGY ICAR - INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI
Abstract
Chickpea (Cicer arietinum L.) is the most important legume crop of the arid zones of
India and has been grown under rain fed conditions since centuries. Most of the
Indian soils harbor a diverse group of rhizobial populations which can nodulate many
leguminous crops. Its economic success depends upon the symbiotic association with
root nodulating bacteria. The most common rhizobia able to nodulate chickpea have
been shown to belong to the genus Mesorhizobium and species of either
Mesorhizobium ciceri or M. mediterraneum. The diversity of Mesorhizobia is
however far from clear, especially considering the large number of chickpea cultivars
and their wide geographical distribution. The genotypic diversity within
Mesorhizobium strains nodulating chickpea has not been very well addressed. The
phylogenetic analysis based on single gene like 16S rRNA is not sufficient enough to
provide clear resolution about the genetic diversity of rhizobia hence polyphasic
approach or multi locus analysis is required to resolve the genetic diversity at species
or strain level. In the present study, 30 Mesorhizobium strains were isolated from
three chickpea cultivars (BGD 72, BG 372, and BGD 547) grown at IARI field, Delhi
and farmers’ field at Hisar, Haryana. The genetic diversity of these isolates were
analysed on the basis of two housekeeping genes (recA, atpD) and two symbiotic
genes (nifH, nodC) along with 16S rRNA. The genetic diversity on the basis of single
loci analysis revealed that three to five different Mesorhizobium species associated
with chickpea. Even though nodule occupancy based on nifH phylogeny was by the
dominant M. mediterraneum 40% and 66.7% (IARI and Hisar respectively) at both
locations, nifH sequences revealed not only the presence of diverse species of
Mesorhizobium in nodules but also further divergence within M. mediterraneum.
Interestingly, the diversification was found lower with nodC phylogeny.
The combined phylogenetic analysis of all loci showed the presence of
Mesorhizobium temperatum, M. mediterraneum, M. septentrionale, M. ciceri, M.
tarimense, M. gobiense, M. tianshanense, M.metallidurans (eight identified species)
and several unknown species of Mesorhizobium in chickpea nodules. Our results
showed the possibility of varietal and location influence on Mesorhizobial species
nodulating chickpea and Multilocus sequencing is essential to delineate the
Mesorhizobium diversity. It is clearly evident that in addition to location specific
strain, there is a need to develop cultivar specific strain(s) as bioinoculant(s) to
improve the overall productivity of chickpea. The study demonstrated that nifH
phylogeny could be used for selecting diverse chickpea symbionts in the field
conditions.
Key words: Chickpea, Mesorhizobium spp., Genotypic diversity, polyphasic
approach
Description
t-9948
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