Characterization of cultivable putative endophytic plant growth promoting bacteria associated with maize cultivars (Zea mays L.) and their inoculation effects in vitro

Maize (Zea mays L.) plants can establish beneficial associations with various nitrogen fixing and plant growth promoting bacteria (PGPB). Twenty-two putative endophytic bacteria isolated from maize plants were identified and characterized by the presence of nifH, IAA production, siderophores and phosphate solubilizing capacity. In addition, inoculation experiments to evaluate plant growth promotion were conducted under laboratory conditions. High diversity of diazotrophic bacteria associated to maize plants was found, including the genera Rhanella, Pantoea, Rhizobium, Pseudomona, Herbaspirillum, Enterobacter, Brevundimonas and Burkholderia. All strains produce IAA in vitro but only P. fluorescens (EMA68) produces siderophores. Phosphate solubilization capability was detected in eighteen strains and Rhanella spp. (EMA83) showed the highest potential. There were significant differences between controls and inoculated plants. Positive effects across maize cultivars were observed with 10 isolates from 22, whose inoculation resulted in an increase on shoot biomass over uninoculated controls without N. H. frisingense, EMA117 was the only strain that showed positive effect on both maize cultivars. It was observed a significant interaction between inoculation treatment x maize cultivars in shoot and root dry weight (P < 0.05). Only one strain, Pseudomona flourescen, increased significantly the growth of the radicle compared to that of the controls without inoculation. In conclusion, maize inoculation experiments showed significant increases in shoot dry weight under controlled conditions but it is not clearly related to IAA production, P solubilization capacity or to more N efficiency assimilation. There is a potential PGPB in maize cultivars, but the results indicate the need for a better understanding of plant-bacteria interactions and to investigate plant colonization by endophytic bacteria. (C) 2012 Elsevier B.V. All rights reserved.