Dual inoculation of a woody legume (Centrolobium tomentosum) with rhizobia and mycorrhizal fungi in south-eastern Brazil M. S. Marques, M. Pagano & M. R. M. M. L. Scotti* Departmento de Botânica/ICB/UFMG, Avenida Antonio Carlos, 6627, Pampulha, Cep: 31.270-901 Belo Horizonte, Minas Gerais, Brasil (*Author for correspondence: Av. Antonio Carlos, 6627, Pampulha, Cep: 31.270-901 Belo Horizonte M.G., Brazil; E-mail: scottimuzzi@ig.com.br) Received 21 December 1999; accepted in revised form 28 October 2000 Key words: arbuscular mycorrhizal fungi, nitrogen fixation, nodulation, revegetation, Rhizobium sp, tropical forest, tropical leguminous tree Abstract The integration of N 2 fixing trees into stable agroforestry systems in the tropics is being tested due to their ability to produce high biomass N and P yields, when symbiotically associated with rhizobia and mycorrhizal fungi. The growth of Centrolobium tomentosum Guill. ex Benth, a native leguminous tree from the Brazilian Atlantic Forest, was assessed with dual inoculation of Rhizobium spp and mycor- rhizal fungi under field conditions. Complete fertilization was compared to treatments of inoculation with selected rhizobia strains BHICB-Ab1 or BHICB-Ab3, associated or not to arbuscular mycorrhizal (AM) fungi. The dual inoculation increased the height and growth in relation to the plants treated with rhizobia alone. Plants inoculated with strain BHICB-Ab1 and arbuscular mycorrhizal fungi (AMF) exhibited an increase of 56% dry matter over uninoculated control and nitrogen accumulation was greater than with BHICB-Ab3 inoculated plants. Strain BHICB-Ab1 presented a synergetic relationship with mycorrhizal fungi since the combined inoculation with BHICB-Ab1 enhanced plant height and dry weight more than single inoculation while the growth of BHICB-Ab3 plants was not modified by AMF inoculation. Arbuscular mycorrhizal fungi enhanced plants survival and seemed to favour the nodule occupation by rhizobia strains as compared to the non-mycorrhizal plants. Inoculation with selected rhizobia and AMF improved the growth of C. tomentosum under field conditions. Agroforestry Systems 52: 107–117, 2001.  2001 Kluwer Academic Publishers. Printed in the Netherlands. Introduction The integration of leguminous trees into agro- forestry systems and silvo-pastoral systems is currently being suggested as a possible solution to the restoration and maintenance of soil fertility especially in nutrient deficient soils of the tropics. Such soils are reclaimed through afforestation programmes with forest tree species which allow renewable sources of fuel and provide other wood products. What discourages many farmers from seriously considering forest production with native species is the slow rate at which vegetation grows and especially the low rates of regeneration of valuable tropical species (Hartshorn, 1995). However, many tropical woody legumes grow rapidly but the success of these species will depend on their ability to symbiotically fix atmospheric nitrogen, which may increase the nitrogen content of imporverished soils and supply nitrogen – rich green manures and high-protein forage (Galiana et al., 1998). Relatively few leguminous trees species have been tested for their nodulating or nitrogen