The H<inf>2</inf>-oxidizing Rhizobacteria Associated with Field-Grown Lentil Promote the Growth of Lentil Inoculated with Hup+ Rhizobium Through Multiple Modes of Action

Certain H2-oxidizing rhizobacteria promote the growth of legume plants nodulated with rhizobia devoid of an uptake hydrogenase system (Hup−). We demonstrated and assessed the plant growth-promoting ability of H2-oxidizing rhizobacteria naturally associating with lentil roots nodulated by rhizobia possessing an uptake hydrogenase system (Hup+ lentil) in semiarid Canada. The ten H2-oxidizing rhizobacteria isolated were strains of Variovorax paradoxus, Variovorax sp., Rhodococcus sp., Mycobacterium sp., Acinetobacter sp., Acinetobacter calcoaceticus, and Curtobacterium sp. Several of these strains increased Hup+ lentil shoot and root biomasses, and root nodule number in the absence or presence of drought stress. Inoculation with H2-oxidizing rhizobacteria enhanced the growth of Hup+ lentil infected by the fungal root pathogens Fusarium avenaceum, Rhizoctonia solani, and Pythium ultimum. Fusarium avenaceum growth was markedly suppressed by all H2-oxidizing rhizobacteria in vitro, and seven isolates also suppressed the growth of both R. solani and P. ultimum. Siderophore production was detected in nine isolates and one isolate could solubilize phosphate. Indole-3-acetic acid production was found in four isolates, and 1-aminocyclopropane-1-carboxylate deaminase activity in six isolates. Most H2-oxidizing rhizobacterial isolates exhibited multiple plant growth-promoting attributes and all isolates exhibited at least one. Our results suggest that the H2-oxidizing rhizobacteria naturally associating with lentil roots in semiarid Canada are beneficial in an Hup+ environment.