Rhizobia and AM fungal inoculation improve growth and nutrient uptake of bean plants under organic fertilization

Potted bean (Phaseolus vulgaris L. cv speed wonder) plants were grown in a glasshouse with and without organic and chemical fertilizers, un-inoculated or inoculated with rhizobia (a mixed culture of Rhizobium leguminosarum bv. phaseoli and R. tropici) and arbuscular mycorrhizal fungi (AMF) (Glomus spp.), singly or in combination. Treatment effects on growth, nodulation, AMF colonization and nutrient uptake of plants were evaluated. Rhizobial inoculation positively influenced root dry weight and nodulation of plants. Shoot and root dry weights and nodulation were again higher in dually inoculated plants compared to singly inoculated plants. Compared to control, single inoculation either with rhizobia or AMF did not increase pod yield. But, dual inoculation significantly increased pod yield compared to control or singly inoculated plants. Inoculation also significantly increased pod yield in organic fertilization treatment, but not in chemical fertilization treatment. AMF colonization, spore population and shoot N and P were also significantly higher in dually inoculated plants. Under fertilized conditions, nodulation, AMF colonization and spore population were generally more pronounced in dually inoculated organic plants than in chemical plants. Shoot Ca, and K remained unaffected by inoculation either in fertilized or unfertilized conditions. Dual inoculation significantly increased the concentration of shoot Mg in organic plants, but not in chemical. In general, better positive effects of inoculations were observed in organic plants than in chemical suggesting higher dependency of organic plants on these symbionts for better growth and development. (C) 2003 by The Haworth Press, Inc. All rights reserved.