Abstract
Chickpea (Cicer arietinum L.) used to be considered a restrictive host that nodulated and fixed nitrogen only with Mesorhizobium ciceri and M. mediterraneum. Recent analysis revealed that chickpea can also establish effective symbioses with strains of several other Mesorhizobium species such as M. loti, M. haukuii, M. amorphae, M. muleiense, etc. These strains vary in their nitrogen fixation potential inviting further exploration. We characterized newly collected mesorhizobial strains isolated from various locations in Ethiopia to evaluate genetic diversity, biogeographic structure and symbiotic effectiveness. Symbiotic effectiveness was evaluated in Leonard Jars using a locally released chickpea cultivar “Nattoli”. Most of the new isolates belonged to a clade related to M. plurifarium, with very few sequence differences, while the total collection of strains contained three additional mesorhizobial genospecies associated with M. ciceri, M. abyssinicae and an unidentified Mesorhizobium species isolated from a wild host in Eritrea. The four genospecies identified represented a subset of the eight major Mesorhizobium clades recently reported for Ethiopia based on metagenomic data. All Ethiopian strains had nearly identical symbiotic genes that grouped them in a single cluster with M. ciceri, M. mediterraneum and M. muleiense, but not with M. plurifarium. Some phylogeographic structure was observed, with elevation and geography explaining some of the genetic differences among strains, but the relation between genetic identity and symbiotic effectiveness was observed to be weak.
Highlights
IntroductionThe relatively poor grain yield is attributed to poor soil fertility combined with a lack of fertilizers [2], related to the common notion among farmers that legume crops do not need nutrient inputs [7]
Chickpea (Cicer arietinum L.) is one of the most important grain legumes globally, with a total production of 11.6 millionElectronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.Addis Ababa, Ethiopia tons from an area of 13.2 million ha and with a productivity of 0.88 tons ha−1 [1]
We report on the taxonomy and patterns of genetic diversity in a set of 21 additional Mesorhizobium strains sampled from Ethiopia, which we combine with published data on 18 strains [30]
Summary
The relatively poor grain yield is attributed to poor soil fertility combined with a lack of fertilizers [2], related to the common notion among farmers that legume crops do not need nutrient inputs [7]. The latter idea may derive in part from the fact that grain legumes like chickpea are able to fix atmospheric nitrogen through symbiosis with rhizobia. This presumes that nitrogen will not be limiting as long as compatible bacteria are present in the soil. It is relevant to understand the taxonomy and diversity of chickpea rhizobia native to Ethiopia
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