Abstract
Studies on the biodiversity of plants associated microorganisms play an important role in food production. Ficus-tree, Opuntia ficus-indica Mill, are cultivated in many nations worldwide intercropping with other cultures, like cowpea, Vigna unguiculata (L.) Walp. The objectives of this study were to isolate and determine the diversity of bacterial endophytes and rhizobacteria in cacti and their ability to solubilize phosphate, the nif presence, their ability to produce indole-acetic acid (IAA) and verify their efficacy to promote plant growth in cowpea plants. Bacteria were isolated from rhizospheric soils, from surface- sterilized stems and roots of plants collected in Brazil, in nitrogen- free medium, and identified through fatty acid analysis. Gram-negative bacteria comprised 63% of endophytic bacteria and 80% of rhizobacteria. Only 13% showed amplification of nifH gene. From the 68 bacterial strains, associated with cacti, 18% produced IAA, and the best results were observed in Agrobacterium radiobacter, Klebsiella trevisanii, Enterobacter agglomeransand Paracoccus denitrificans. Phosphate solubilization was observed in 6% of strains. None of the strains inoculated in cowpea plants promoted stem and foliar growth. Four percent of strains showed ability to increase the root dry matter compared to the control group (inoculated with a pool of indigenous semi-arid Rhizobium). Key words: Endophytes, rhizosphere, indole-acetic acid (IAA), phosphate solubilization, cacti, Vigna. .
Highlights
Microbial diversity assessments presume that the number of interacting species can be identified, classified and their respective activities extrapolated to their function in different agricultural systems
From the 68 bacterial strains, associated with cacti, 18% produced indole-acetic acid (IAA), and the best results were observed in Agrobacterium radiobacter, Klebsiella trevisanii, Enterobacter agglomerans and Paracoccus denitrificans
It is well known that a considerable number of bacterial species, mostly associated with the plant rhizosphere, are able to exert a beneficial effect on plant growth
Summary
Microbial diversity assessments presume that the number of interacting species can be identified, classified and their respective activities extrapolated to their function in different agricultural systems. Endophytic bacteria could promote plant growth and yield by enhancing soil fertility through phosphate solubilization and nitrogen fixation (Ryan et al, 2007). It is well known that a considerable number of bacterial species, mostly associated with the plant rhizosphere, are able to exert a beneficial effect on plant growth. This group of bacteria has been termed plant growth promoting rhizobacteria (PGPR). The mechanisms through which PGPR may stimulate plant growth are probably due to the production of indole-3-acetic acid (IAA) and cytokinin-like compounds as well as by lowering ethylene levels in plants (Ali et al, 2009); fixing nitrogen (Zaidi and Mohammad, 2006), and increasing
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