چکیده (انگلیسی):

The main objective of the present study was to isolate phytohormone-producing,phosphate-solubilizing strains of Azospirillum from wheat to be used as inoculants for plantgrowth promotion. Five Azospirillum strains were isolated from the rhizosphere of field-grown wheat (Triticum aestivum L.), and it was confirmed by BOX-polymerase chain reaction(PCR) that the isolates were different and not re-isolates of the same strain. Sequence anal-ysis of the PCR-amplified 16S rRNA gene indicated that four isolates showed maximumsimilarity to Azospirillum brasilense and one isolate showed maximum similarity to Azospir-illum zeae. This is the first report indicating the presence of an A. zeae like isolate in thewheat rhizosphere in Pakistan. The bacterial isolates were characterized for their plantgrowth-promoting traits, phosphate solubilization, and indole-3-acetic acid (IAA) produc-tion. None of the isolates showed phosphate solubilization activity in the commonly usedPikovskaya medium. However, all strains (except AzoK4) exhibited ability to solubilize tri-calcium phosphate (TCP) in modified Pikovskaya medium in which sucrose was replacedby Na-malate, as well as in TCP-supplemented Luria-Bertani (LB) medium. Organic acids,such as acetic, citric, lactic, malic, and succinic acids, were detected in culture supernatantsof the tested Azospirillum strains. All strains exhibited ability to produce IAA in the growthmedium, except Azospirillum sp. AzoK1. Among the strains tested, the maximum IAA pro-duction (30.49 ± 1.04 mg L−1) and phosphate solubilization (105.50 ± 4.93 mg L−1) were shownby a pure culture of Azospirillum sp. AzoK2. In pot experiments, single-strain inocula ofAzospirillum sp. AzoK1 and AzoK2 improved wheat plant growth.© 2016 Published by Elsevier Editora Ltda. on behalf of Sociedade Brasileira deMicrobiologia. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).