Co-inoculation of a Pea Core-Collection with Diverse Rhizobial Strains Shows Competitiveness for Nodulation and Efficiency of Nitrogen Fixation Are Distinct traits in the Interaction

Abstract

Pea forms symbiotic nodules with Rhizobium leguminosarum sv. viciae (Rlv). In the field, pea roots can be exposed to multiple compatible Rlv strains. Little is known about the mechanisms underlying the competitiveness for nodulation of Rlv strains and the ability of pea to choose between diverse compatible Rlv strains. The variability of pea-Rlv partner choice was investigated by co-inoculation with a mixture of five diverse Rlv strains of a 104-pea collection representative of the variability encountered in the genus Pisum. The nitrogen fixation efficiency conferred by each strain was determined in additional mono-inoculation experiments on a subset of 18 pea lines displaying contrasted Rlv choice. Differences in Rlv choice were observed within the pea collection according to their genetic or geographical diversities. The competitiveness for nodulation of a given pea-Rlv association evaluated in the multi-inoculated experiment was poorly correlated with its nitrogen fixation efficiency determined in mono-inoculation. Both plant and bacterial genetic determinants contribute to pea-Rlv partner choice. No evidence was found for co-selection of competitiveness for nodulation and nitrogen fixation efficiency. Plant and inoculant for an improved symbiotic association in the field must be selected not only on nitrogen fixation efficiency but also for competitiveness for nodulation.

Modelling predicts that soybean is poised to dominate crop production across Africa

“…However, these bacteria can have equal N‐fixation ability when partnered with certain Chinese soybean varieties, and some soybean genotypes are able to differentially restrict nodulation by specific serogroups of Bradyrhizobium or Sinorhizobium strains. Identification of genes that either exclude or substantially reduce nodulation by ineffective indigenous strains will be invaluable in improving the efficiency of symbiotic nitrogen fixation in African soils (Andrews & Andrews, ; Bourion et al, ).…”

Legume nodulation: The host controls the party

“…Rhizobia strains and legume varieties tolerant to various abiotic stresses have been isolated through laboratory and glasshouse experiments, but thorough field experiments are needed to confirm they are effective in field conditions (Thilakarathna & Raizada, 2017). Parasitic rhizobia strains that effectively colonize legumes, without resulting in optimal nitrogen fixation have also been isolated, and these pose a significant problem to agriculture (Bourion et al, 2017;Laguerre, Louvrier, Allard, & Amarger, 2003). However, local and systemic plant signalling mechanisms that follow initial nodulation events, such as AON, help to ensure adequate nitrogen acquisition via symbiosis in less than ideal partnerships (Jeudy et al, 2010;Laguerre et al, 2012).…”

Host‐specific competitiveness to form nodules in Rhizobium leguminosarum symbiovar viciae

“…Pioneer studies showed that CFN was not associated with the ability to fix nitrogen in Sinorhizobium/Medicago sativa associations (Amarger, ). Co‐inoculation of a mixture of diverse pea‐nodulating Rlv strains on a panel of 104 pea genotypes, representative of the variability of the genus Pisum , revealed that the CFN varied greatly depending on both pea and Rlv genotypes and it was not associated with BNF efficiency (Bourion et al , ). Plants may sanction BNF‐inefficient partners by reducing the number of cultivable cells present in nodules (Kiers et al , ) and preferentially stimulate the growth of symbiotic organs formed with most BNF‐efficient rhizobia (Laguerre et al , ).…”