Endophytic and rhizospheric bacteria from Opuntia ficus-indica mill and their ability to promote plant growth in cowpea, Vigna unguiculata (L.) Walp

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. .