The role of nutrients underlying interactions among root-nodule bacteria (Bradyrhizobium sp.), arbuscular mycorrhizal fungi (Funneliformis mosseae) and root-lesion nematodes (Pratylenchus thornei) in nitrogen fixation and growth of mung bean (Vigna radiata)

Purpose To investigate the role nutrients play in arbuscular mycorrhizal fungal improvement of biological nitrogen fixation (BNF) by Bradyrhizobium sp. and increases in Pratylenchus thornei (Sher & Allen) population density in mung bean ( Vigna radiata (L.) R. Wilczek). Methods A glasshouse experiment was conducted on mung bean with 2 6 factorial treatments of AMF, rhizobia, P. thornei , nitrogen (N), phosphorus (P) and zinc (Zn) in a pasteurised vertisol. Variates of biomass, yield, nodulation, natural abundance δ 15 N, mycorrhizal colonisation, nutrients in the plant shoot and P. thornei multiplication were assessed at 6 and 11 weeks. Results The combination of AMF and P improved BNF in the shoots at 6 weeks, while AMF alone improved BNF and nodulation greater than the addition of P at 11 weeks. Inoculation with AMF increased the shoot concentrations of P and Zn greater than fertilisation with either nutrient alone. Seed yield and biomass were similar when AMF or P was each applied alone with no further increase when combined. Rhizobia increased seed yield greater than the addition of N. Inoculation with AMF and rhizobia increased yield and biomass greater than rhizobia alone, and to a higher level than inoculation with AMF and fertiliser N. Pratylenchus thornei populations in the roots increased with AMF, but the addition of N, P and Zn decreased them. Conclusions AMF increase supply of P to mung bean, improving BNF by Bradyrhizobium , yield and crop nutrition while reducing fertiliser inputs. Active management to ensure effective AMF colonisation and reduced P. thornei reproduction is warranted.