ORIGINAL PAPER Arbuscular mycorrhizal colonization and nodulation improve flooding tolerance in Pterocarpus officinalis Jacq. seedlings L. Fougnies & S. Renciot & F. Muller & C. Plenchette & Y. Prin & S. M. de Faria & J. M. Bouvet & S. Nd. Sylla & B. Dreyfus & A. M. Bâ Received: 20 June 2006 / Accepted: 16 October 2006 / Published online: 2 December 2006 # Springer-Verlag 2006 Abstract Pterocarpus officinalis (Jacq.) seedlings inocu- lated with the arbuscular mycorrhizal fungus, Glomus intraradices, and the strain of Bradyrhizobium sp. (UAG 11A) were grown under stem-flooded or nonflooded conditions for 13 weeks after 4 weeks of nonflooded pretreatment under greenhouse conditions. Flooding of P. officinalis seedlings induced several morphological and physiological adaptive mechanisms, including formation of hypertrophied lenticels and aerenchyma tissue and produc- tion of adventitious roots on submerged portions of the stem. Flooding also resulted in an increase in collar diameter and leaf, stem, root, and total dry weights, regardless of inoculation. Under flooding, arbuscular mycorrhizas were well developed on root systems and adventitious roots compared with inoculated root systems under nonflooding condition. Arbuscular mycorrhizas made noteworthy contributions to the flood tolerance of P. officinalis seedlings by improving plant growth and P acquisition in leaves. We report in this study the novel occurrence of nodules connected vascularly to the stem and nodule and arbuscular mycorrhizas on adventitious roots of P. officinalis seedlings. Root nodules appeared more efficient fixing N 2 than stem nodules were. Beneficial effect of nodulation in terms of total dry weight and N acquisition in leaves was particularly noted in seedlings growing under flooding conditions. There was no additive effect of arbuscular mycorrhizas and nodulation on plant growth and nutrition in either flooding treatment. The results suggest that the development of adventitious roots, aerenchyma tissue, and hypertrophied lenticels may play a major role in flooded tolerance of P. officinalis symbiosis by increasing oxygen diffusion to the submerged part of the stem and root zone, and therefore contribute to plant growth and nutrition. Keywords Arbuscular mycorrhizas . Glomus intraradices . Mycorrhizal adventitious roots . Bradyrhizobium . Stem nodules Mycorrhiza (2007) 17:159–166 DOI 10.1007/s00572-006-0085-2 L. Fougnies : S. Renciot : F. Muller : A. M. Bâ Laboratoire de biologie et physiologie végétales, Faculté des sciences exactes et naturelles, Université Antilles-Guyane, BP. 592, Pointe-à-Pitre, Guadeloupe 97159, France F. Muller : Y. Prin : B. Dreyfus : A. M. Bâ (*) Laboratoire des symbioses tropicales et méditerranéennes, UMR 113 IRD/INRA/AGRO-M/CIRAD/UM2, TA10/J, Campus international de Baillarguet, 34398 Montpellier Cedex, France e-mail: amadou.ba@univ-ag.fr F. Muller : J. M. Bouvet Laboratoire de génétique forestière, CIRAD-Forêt, TA 10/C, Campus international de Baillarguet, 34398 Montpellier Cedex, France C. Plenchette INRA, UMR BGA, 17 rue Sully, 21065 Dijon Cedex, France S. M. de Faria CNPAD/EMBRAPA, Seropédica, Itaguai, Rio de Janeiro 23851-970, Brazil S. N. Sylla Laboratoire commun de microbiologie ISRA/IRD/UCAD, centre de Bel-Air, BP. 1786, Dakar, Sénégal