Abstract
We studied symbiotic performance of factorial combinations of diverse rhizobial genotypes (GR) and East African common bean varieties (GL) that comprise Andean and Mesoamerican genetic groups. An initial wide screening in modified Leonard jars (LJ) was followed by evaluation of a subset of strains and genotypes in pots (contained the same, sterile medium) in which fixed nitrogen was also quantified. An additive main effect and multiplicative interaction (AMMI) model was used to identify the contribution of individual strains and plant genotypes to the GL × GR interaction. Strong and highly significant GL × GR interaction was found in the LJ experiment but with little evidence of a relation to genetic background or growth habits. The interaction was much weaker in the pot experiment, with all bean genotypes and Rhizobium strains having relatively stable performance. We found that R. etli strain CFN42 and R. tropici strains CIAT899 and NAK91 were effective across bean genotypes but with the latter showing evidence of positive interaction with two specific bean genotypes. This suggests that selection of bean varieties based on their response to inoculation is possible. On the other hand, we show that symbiotic performance is not predicted by any a priori grouping, limiting the scope for more general recommendations. The fact that the strength and pattern of GL × GR depended on growing conditions provides an important cautionary message for future studies.IMPORTANCE The existence of genotype-by-strain (GL × GR) interaction has implications for the expected stability of performance of legume inoculants and could represent both challenges and opportunities for improvement of nitrogen fixation. We find that significant genotype-by-strain interaction exists in common bean (Phaseolus vulgaris L.) but that the strength and direction of this interaction depends on the growing environment used to evaluate biomass. Strong genotype and strain main effects, combined with a lack of predictable patterns in GL × GR, suggests that at best individual bean genotypes and strains can be selected for superior additive performance. The observation that the screening environment may affect experimental outcome of GL × GR means that identified patterns should be corroborated under more realistic conditions.
Highlights
We studied symbiotic performance of factorial combinations of diverse rhizobial genotypes (GR) and East African common bean varieties (GL) that comprise Andean and Mesoamerican genetic groups
CIAT899, R. phaseoli ATCC 14482, R. multihospitium LMG23946, and S. meliloti LMG6133) and revealed that the three East African strains (Rhizobium sp. strains NAE136, NAE182, and NAK91) each fell into distinct genetic clusters (Fig. 1a)
The East African strains are all of the Rhizobium genus, with strain NAE136 representing a distinct phylogenetic lineage closely related to R. etli CFN42 and R. aethiopicum HBR26
Summary
We studied symbiotic performance of factorial combinations of diverse rhizobial genotypes (GR) and East African common bean varieties (GL) that comprise Andean and Mesoamerican genetic groups. It is widely thought that common bean (here referred to as “bean”) has low N2 fixation potential compared to other legumes [5,6,7], but reports of strong positive responses to inoculation [6,7,8,9,10] suggest that this can be overcome by providing highly effective rhizobia in abundance. Some studies seem to confirm this [15, 16], others have observed strong responses in soils with very high rhizobial population densities [17, 18] The latter suggests that symbiotic effectiveness, of either the inoculant or the local population, rather than abundance of indigenous rhizobia, is an issue. We consider all three aspects as potential determinants of inoculation success
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
