Arbuscular mycorrhizal fungi acted synergistically with Bradyrhizobium sp. to improve nodulation, nitrogen fixation, plant growth and seed yield of mung bean (Vigna radiata) but increased the population density of the root-lesion nematode Pratylenchus thornei

Purpose Mung bean is a host of the root-lesion nematode Pratylenchus thornei (Sher & Allen) and the beneficial symbionts arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing Bradyrhizobium bacteria. The purpose of this research was to investigate interactions among these organisms affecting their reproduction and functional impact on mung bean nodulation, nutrition, biological nitrogen fixation, growth and seed yield. Methods A glasshouse experiment was conducted with mung bean in pots of a pasteurised vertisol using a factorial design of treatments to investigate the interactive effects of AMF, Bradyrhizobium and P. thornei. The plants were assessed at 6 and 12 weeks after sowing for variables of shoot biomass, seed yield, nodulation, P. thornei population density, AMF colonisation of the roots, and nutrients in the plant shoot, including nitrogen isotope natural abundance (delta N-15) to quantify fixed nitrogen. Results Arbuscular mycorrhizal fungi and rhizobia acted synergistically to substantially increase nodulation, nitrogen fixation, nutrition, seed yield and biomass of the plants. The population density of P. thornei in roots of the mung bean at 12 weeks increased in plants inoculated with AMF and was positively correlated with plant nutrition namely increased phosphorus, zinc and copper concentrations in the plant shoot. Conclusion Understanding these interactions should inform changes in agronomic practices, to promote the synergism between mycorrhiza and rhizobia for mung bean yield, while managing to limit P. thornei population densities to benefit mung bean itself and subsequent crops in the farming system.

Automated summary

Arbuscular mycorrhizal fungi and rhizobia act synergistically to enhance nodulation, nitrogen fixation, nutrition, seed yield, and biomass of mung bean plants. The population density of P. thornei in roots increased in plants inoculated with AMF, positively correlated with plant nutrition, specifically phosphorus, zinc, and copper concentrations in the plant shoot.