Genetic Diversity, Ecophysiological Characteristics and Symbiotic Effectiveness of Chickpea Nodulating Rhizobia from The Central and Northern Ethiopia
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Date
2019-04-04
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Addis Ababa University
Abstract
Chickpea has the ability to fix atmospheric nitrogen in symbiosis with diverse Mesorhizobium spp. However, there are evidences to suggest that the diversity of rhizobial symbionts is associated with geographic origin. This study investigated the genetic diversity and distribution of chickpea rhizobia in the central and northern parts of Ethiopia using sequence analyses of the housekeeping recA gene and the symbiotic genes of nodA and nifH. A total of 132 chickpea rhizobial isolates were collected from different sites. The phylogenetic analysis of the recA gene revealed that the isolates belonged to the Mesorhizobium genus. The strains are highly diverse phylotypes grouped into seven genospecies (GI-VII). Most of the isolates (38.6%) were closely related to M. plurifarium (GI) and 25.8% of the isolates were clustered with M. amorphae (GII). Only 15.9% of the isolates were related to M. ciceri (GIII) and no isolate were associated to M. mediterraneum, the two common chickpea rhizobial species. The other isolates were grouped to M. shonense (GIV) (9.8%) and M. abyssinicae (GVI) (2.3%), and two potentially new chickpea nodulating symbiovars; M. hawassense (GVI) and M. gobiense (GVII) comprising 6.1% and 1.5% of the isolates, respectively. All isolates shared high sequence similarity with nodA and nifH genes of the typical chickpea rhizobia; M. ciceri and M. mediterraneum, irrespective of their difference in their sequence similarity to the housekeeping gene and sites of isolation. This suggests that these diverse chickpea Mesorhizobium strains acquired symbiosis genes from the common origin, which might be from the co-occurring natural chickpea rhizobia symbionts such as M. ciceri. The sequence data also showed that the three major genomic groups related to M. plurifarium, M. amorphae and M. ciceri were widely distributed in all sites. The other four minor groups were isolated from some sites of Shoa, Gojam or Gondar. In general, more diverse genospecies (at least 5 different groups) were distributed in Gondar, Gojam and Shoa compared to fewer genospecies identified from Wollo and Tigray sites. The correspondence analysis also indicated that the diversity and local distribution of the chickpea rhizobia might be associated with soil characteristics such as available phosphorus (AP), available potassium (AK), pH and salinity of the sampling soils. The results generally showed that Ethiopian soils harbor highly diverse and distinct chickpea nodulating symbionts. Therefore, selecting elite strains among these genetically diverse rhizobia for better symbiotic nitrogen fixation would be expected to improve chickpea production for stallholder farmers.
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Chickpea, Genetic Diversity, Mesorhizobium, Phylogeny, Symbiotic Genes