Bacillus sp. strain CaSUT007, a plant growth promoting rhizobacterium isolated from cassava, was investigated for the secretion of compounds that might be involved in plant growth promotion. Extracts containing phytohormone and extracellular proteins were made from the cell-free fluid of CaSUT007 broth cultures. These extracts, along with a whole culture of CaSUT007 and the raw fluid and cellular fractions from a CaSUT007 culture, were applied separately to cassava stakes. The stakes were planted into pots of soil maintained in a greenhouse condition. Under this condition, all of the extracts including phytohormones and extracellular proteins increased root and shoot lengths and cassava biomass as compared to negative control. Our results indicate that the culture extracts, when applied to cassava stakes, increased root and shoot lengths by more than 30%, and increased fresh and dry weights by more than 25% compared to the distilled water control. Thus, photohormone and extracellular proteins secreted by CaSUT007 can influence plant growth and development. Analysis of the photohormone and extracellular proteins extracts revealed indole-3-acetic acid and peptides to be the primary compounds.
Key words: Cassava, growth promotion, Bacillus, extracellular proteins, phytohormone.
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