Synergistic Plant Growth Promotion by the Indigenous Auxins-producing PGPR Bacillus subtilis AH18 and Bacillus licheniforims K11

In this study, we invested the synergistic plant promotion ability of red-pepper and tomato by the selected multi-functional PGPR: Bacillus subtilis AH18 and Bacillus licheniformis K11. The both strains of PGPR B. licheniformis K11 and B. subtilis AH18 produced the auxins, antifungal beta-glucannase, and siderophores, and were capable of solubilizing insoluble phosphates. The auxins produced by B. subtilis AH18 and B. licheniformis K11 were purified and identified from culture filtrates using PVP column, Sephadex LH-20 column chromatography, HPLC, GC-MS, and H-1-NMR. The purified auxin(AH18) was confirmed to have derivatives composed with IAA of MW 175, IBA of MW 203, and IPA of MW 189. The amount ratio of auxin(AH18) producing was as follows: IAA:IBA:IPA=1:1.5:2.6. The purified auxin(K11) consisted of an IBA of MW 203. B. licheniformis K11 and B. subtilis AH18 stimulated seed germination and root growth of red-pepper, tomato, green onions, and spinach. In particular, red-pepper and tomato plants displayed up to 20% increased root, stem, and leaf growth. When the pots were simultaneously treated with a combination of auxin(AH18) and auxin(K11) the growth rates of red pepper and tomato plants were over 20% greater than observed with treatment with either auxin alone.