EFFECT OF ARBUSCULAR MYCORRHIZAL FUNGI ON GROWTH, MINERAL-NUTRITION AND NITROGEN-FIXATION OF 3 VARIETIES OF COMMON BEANS (PHASEOLUS-VULGARIS)

A pot experiment was conducted under glasshouse conditions to investig ate the effect of inoculation with four arbuscular mycorrhizal (AM) fu ngi (Glomus clarum, G. etunicatum, G. manihotis, Gigaspora margarita), either individually or in a mixture, and with Rhizobium leguminosarum biovar phaseoli, on the growth, mineral nutrition, and contribution o f biologically fixed N-2, to three nodulating bean (Phaseolus vulgaris ) varieties (Carioca, Negro Argel and Rio Tibagi). The N-15 isotope di lution technique and three control crops (non-nodulating bean, Panicum maximum and sorghum) were used to quantify the contribution of N-2 fi xation. There were significant differences between the capacity of the different AM fungi to infect and colonize the roots of the different bean varieties. Inoculation with AM fungi significantly increased prod uction of dry matter by 8-23% and the concentration of P in plants by 160-335%. A strongly positive correlation of % root colonization by AM fungi and plant P concentration and accumulation was observed which s uggests that the observed inoculation responses were a result of impro ved P acquisition by the mycorrhizal roots. N derived from the atmosph ere increased significantly with AM fungi inoculation, with Carioca sh owing the best response, followed by Negro Argel and Rio Tibagi, there by showing the indirect and positive effect of AM fungi inoculation on the N-2-fixing association between Rhizobium and Phaseolus vulgaris.