Micorrizas

Mycorrhiza (2009) 19:81–90 DOI 10.1007/s00572-008-0205-2

ORIGINAL PAPER

Bacterial effects on arbuscular mycorrhizal fungi and mycorrhiza development as influenced by the bacteria, fungi, and host plant
Barbara Pivato & Pierre Offre & Sara Marchelli & Bruno Barbonaglia & Christophe Mougel & Philippe Lemanceau & Graziella Berta

Received: 14 May 2008 / Accepted: 25 September 2008 /Published online: 22 October 2008 # Springer-Verlag 2008

Abstract Bacterial strains from mycorrhizal roots (three belonging to Comamonadaceae and one to Oxalobacteraceae) and from non-mycorrhizal roots (two belonging to Comamonadaceae) of Medicago truncatula and two reference strains (Collimonas fungivorans Ter331 and Pseudomonas fluorescens C7R12) were tested for their effect on the in vitrosaprophytic growth of Glomus mosseae BEG12 and on its colonization of M. truncatula roots. Only the Oxalobacteraceae strain, isolated from barrel medic mycorrhizal roots, and the reference strain P. fluorescens C7R12 promoted both the saprophytic growth and root colonization of G. mosseae BEG12, indicating that they acted as mycorrhiza helper bacteria. Greatest effects were achieved by P. fluorescensC7R12 and its influence on the saprophytic growth of G. mosseae was compared to that on Gigaspora rosea BEG9 to determine if the bacterial stimulation was fungal specific. This fungal specificity, together with plant specificity, was finally evaluated by comparing bacterial effects on arbuscular mycorrhizal symbiosis when each of the fungal species was inoculated to two different plant species (M.truncatula and Lycopersicon esculentum). The results obtained showed
B. Pivato : S. Marchelli : B. Barbonaglia : G. Berta Università del Piemonte Orientale ‘Amedeo Avogadro’, I-15100 Alessandria, Italy B. Pivato : P. Offre : C. Mougel : P. Lemanceau INRA, Université de Bourgogne, UMR 1229 ‘Microbiologie du Sol et de l’Environnement’, CMSE, 21065 Dijon, France P. Lemanceau (*) UMR Microbiologie duSol et de l’Environnement, INRA/Université de Bourgogne, CMSE, BP 86510, 21065 Dijon cedex, France e-mail: philippe.lemanceau@dijon.inra.fr

that promotion of saprophytic growth by P. fluorescens C7R12 was expressed in vitro towards G. mosseae but not towards G. rosea. Bacterial promotion of mycorhization was also expressed towards G. mosseae, but not G. rosea, in roots of M. truncatula and L.esculentum. Taken together, results indicated that enhancement of arbuscular mycorrhiza development was only induced by a limited number of bacteria, promotion by the most efficient bacterial strain being fungal and not plant specific. Keywords Arbuscular mycorrhizas . Comamonadaceae . Oxalobacteraceae . Pseudomonas fluorescens C7R12 . Mycorrhiza helper bacteria

Introduction Arbuscular mycorrhizas(AM) are symbiotic associations which occur between the large majority of land plant families (Wang and Qiu 2006) and obligate biotrophic AM fungal species belonging to the Glomeromycota phylum (Schüßler et al. 2001). The AM association represents an ancient symbiosis with fossil evidence dating back to 400 millions years (Remy et al. 1994) and it has been proposed that AM have contributed to thecolonization of land by early plants (Pyrozinski and Malloch 1975; Redecker et al. 2000). AM have a central position in terrestrial nutrient cycling processes and are of particular interest because of their positive effects on plant growth and health and protection against biotic and abiotic stresses (Smith and Read 1997; Cordier et al. 1998; Barea et al. 2002; Berta et al. 2005). Even if AMassociations are generally considered to be non-specific (Sanders 2002), reciprocal interactions based

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Mycorrhiza (2009) 19:81–90

on feedback mechanisms between plants and AM fungi have been proposed (Bever et al. 2002) based on observations of differential responses of plant species to individual isolates and species of AM fungi (Streitwolf-Engel et al. 1997) which lead to variations...