Improvement of forage production in Calliandra calothyrsus: methodology for the identification of an effective inoculum containing Rhizobium strains and arbuscular mycorrhizal isolates

The overall aim of this paper is to describe the selection of effective rhi zobia and arbuscular mycorrhizas (AM), which after inoculation, will signif icantly improve the forage production of Calliandra calothyrsus under field conditions. To achieve this objective, the following activities were carri ed out: (i) establishment from both nodules and soil samples of a collectio n of microsymbionts (rhizobium and ANP of C. calothyrsus from Central Ameri ca (Mexico, Honduras, Guatemala, Nicaragua and Costa Rica), also from outsi de its native range in Cameroon, Kenya and New Caledonia; (ii) identificati on under glasshouse conditions of the most effective rhizobia and AM isolat es; (i) production of a solid selected inoculum for field trials; (iv) exam ination of the impact of the inoculation on the growth of C. calothyrsus mo nitored under nursery conditions. We have screened 446 rhizobia strains in the nursery and identified six as being very effective at nodulating the ho st plant. They originated from Costa Rica (CCCR15 and, CCCR1), from New Cal edonia (CCNC26), from Cameroon (CCC22) and from Kenya (KWN35 and KCC6). In relation to AM, five isolates have been selected for the ability to infect and promote growth of the thost plant-two isolates of Gigaspora albida isol ated from Kenya (GA1b and GA2); one isolate of Scutellospora verrucosa isol ated from Kenya (SV2c); one isolate of Scutellospora calospora isolated fro m Guatemala (SC2) and one isolate of Glomus etunicatum isolated from Hondur as (GE1). Further experiments will test these selected inocula, singly and in mixtures, in order to obtain an inoculant which significantly improves t he growth of C. calothyrsus and to enable its distribution to farmers who u se this woody legume for forage production on their farms. (C) 2001 Elsevie r Science B.V. All rights reserved.