AEM Accepts, published online ahead of print on 23 October 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.01887-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Bradyrhizobia Nodulating the Acacia mangium x A. auriculiformis Interspecific Hybrid are Specific and Differ from those Associated to Both Parental Species

Christine Le Roux, Diana Tentchev, Yves Prin, Doreen Goh, Yani Japarudin, Marie-Mathilde Perrineau, Robin Duponnois, Odile Domergue, Philippe de Lajudie, and Antoine Galiana^*

CIRAD, UMR LSTM, F-34398 Cedex 5, Montpellier, France; IRD, UMR LSTM, F-34398 Cedex 5, Montpellier, France; INRA, UMR LSTM, F-34398 Cedex 5, Montpellier, France; YSG Biotech Sdn. Bhd., Plant Biotechnology Laboratory, P.O. Box 11623, 88817 Kota Kinabalu, Sabah, Malaysia; Sabah Softwoods Sdn. Bhd., P.O. Box 60966, 91019 Tawau, Sabah, Malaysia

^* To whom correspondence should be addressed. Email: galiana{at}cirad.fr.

In the context of an increasing utilisation of the interspecific hybrid Acacia mangium x A. auriculiformis as a plantation tree in the tropical humid zone, its symbiotic characterisation was carried out in comparison with that of its two parental species. Rhizobium strains of diverse geographical origins were isolated from root nodules of the hybrid and its parents. Almost all Acacia hybrid isolates were fast-growing on YEM medium conversely to those isolated from both parental species that were mostly slow-growing. The rhizobium strains were characterised through partial sequencing of the rRNA operon. In the phylogenetic tree, almost all strains isolated from the hybrid were grouped together in a clade close to Bradyrhizobium japonicum while all strains isolated from both parental species were close to Bradyrhizobium elkanii. Inoculation experiments performed in in vitro or greenhouse conditions showed that all strains were infective with their original hosts but exhibited very variable effectivities according to the host plant tested. Thus, homologous strain-host associations were more effective than heterologous ones. This shows that there is still a high potential for isolating and testing new strains from hybrids to be used as inoculants in the frame of large scale afforestation programmes.