Rhizobacteria for reduced fertilizer inputs in wheat (Triticum aestivum spp. vulgare) and barley (Hordeum vulgare) on Aridisols in Turkey

The present study assessed the effect of seed inoculation with single or multiple plant growth-promoting rhizobacterial (PGPR) strains on yield in spring wheat (Triticum aestivum spp. vulgare var. Kırık) and barley (Hordeum vulgare cv. Tokak) plants in both greenhouse and field conditions during the years 2007 and 2008. The treatments of wheat and barley plants during the first year included: (1) Control (no inoculation and no fertilizer), (2) Bacillus OSU-142 (B.OSU-142), (3) Bacillus megaterium M3 (B. megaterium M3), (4) Azospirillum brasilense Sp.245 (A. brasilense Sp.245), (5) Mixed 1 (B.OSU-142 + Bacillus M3 + Azospirillum AB-245), (6) Bacillus megaterium RC07 (B. megaterium RC07), (7) Paenibacillus polymyxa RC05, (8) Bacillus licheniformis RC08, (9) mineral nitrogen N1 (80 kg N ha-1) and (10) N2 (40 kg N ha-1 in the form of urea). In the second year treatments were: (1) Raoutella terrigena (R. Terrigena), (2) Burkholderia cepacia FS Tur (B. cepacia FS Tur), (3) B. OSU-142 ARM, (4) B. M3 ARM, (5) A. sp.245 ARM, (6) P. polymyxa RC14, (7) B. megaterium RC10, (8) Mixed 2 (Bacillus OSU-142+ Bacillus M3+ Azospirillum brasilense sp.245 + 40 kg N ha) in addition to the first year treatments. Greenhouse and the two years of field trials at two sites showed that seed inoculation with bacterial strains significantly affected yield, yield components and quality parameters both in spring wheat and barley. In greenhouse trials, single inoculations of seeds with PGPRs gave root and shoot weight increases by 11.0-16.5% and 14.4-30.4% in wheat and by 10.3-18.8% and 11.9-21.5% in barley. Combinations of three bacteria increased root and shoots weight by 18.3-31.5% in wheat and by 21.4-23.8 in barley and bacterial inoculations also increased grain yield by 4.3-18.5% in wheat and 8.3-19.1% in barley, respectively. In field conditions wheat grain yields were increased by 25.6-40.4%, 17.4-25.2% and 31.4% while barley seed yield were increased by 16.2-33.7%, 4.2-14.4 and 16.8% with N fertilizer, single and combinations of PGPR bacteria inoculations compared to control. Plant-growth responses were variable and depended on the inoculants strain, plant species and growth parameters evaluated. In conclusion, seed inoculations with bacteria especially B. OSU-142, A. brasilense sp.245 and combinations of bacteria may satisfy nitrogen requirements of wheat and barley under green house and field conditions even in lowland and upland areas. The present results indicate that the selected bacterial isolates and multiple combinations did promote the growth and quality of wheat and barley in ways that could be harnessed to practical benefit for the farmer and consistent with sustainable and/or organic agricultural practices in Turkey. Keywords: Aridisol; Biofertilizers; Plant growth-promoting bacteria (PGPR).