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Accueil | Français » Publications » Articles scientifiques » Differing Courses of Genetic Evolution of Bradyrhizobium Inoculants as (...)

Differing Courses of Genetic Evolution of Bradyrhizobium Inoculants as Revealed by Long-Term Molecular Tracing in Acacia mangium Plantations

2014- M. M. Perrineau,a C. Le Roux,a A. Galiana,a A. Faye,b R. Duponnois,d D. Goh,c Y. Prin,a G. Bénad
CIRAD, Laboratoire des Symbioses Tropicales et Méditerranéennes, Montpellier, Francea ; ISRA, Laboratoire Commun de Microbiologie, Dakar, Sénégalb ; Plant
Biotechnology Laboratory, Yayasan Sabah Group, Kota Kinabalu, Sabah, Malaysiac ; IRD, Laboratoire des Symbioses Tropicales et Méditerranéennes, Montpellier, Franced.

Introducing nitrogen-fixing bacteria as an inoculum in association with legume crops is a common practice in agriculture. However,
the question of the evolution of these introduced microorganisms remains crucial, both in terms of microbial ecology and
agronomy. We explored this question by analyzing the genetic and symbiotic evolution of two Bradyrhizobium strains inoculated
on Acacia mangium in Malaysia and Senegal 15 and 5 years, respectively, after their introduction. Based on typing of several
loci, we showed that these two strains, although closely related and originally sampled in Australia, evolved differently. One
strain was recovered in soil with the same five loci as the original isolate, whereas the symbiotic cluster of the other strain was
detected with no trace of the three housekeeping genes of the original inoculum. Moreover, the nitrogen fixation efficiency was
variable among these isolates (either recombinant or not), with significantly high, low, or similar efficiencies compared to the
two original strains and no significant difference between recombinant and nonrecombinant isolates. These data suggested that
15 years after their introduction, nitrogen-fixing bacteria remain in the soil but that closely related inoculant strains may not
evolve in the same way, either genetically or symbiotically. In a context of increasing agronomical use of microbial inoculants
(for biological control, nitrogen fixation, or plant growth promotion), this result feeds the debate on the consequences associated
with such practices.