Plant growth-promoting rhizobacteria associated to candelilla rhizosphere (Euphorbia antisyphilitica) and its effects on Arabidopsis thaliana seedlings

Maria T Salazar-Ramírez,Manuel Fortis-Hernández,Edgar O Rueda-Puente,Pablo Yescas-Coronado,Jorge Sáenz-Mata,Jorge A Orozco-Vidal,Pablo Preciado-Rangel

doi:10.15835/nbha49212294

Abstract

In the communities of Sierra Mojada and Viesca, Coahuila, Mexico of Coahuila desert, two rhizosphere samplings of candelilla (Euphorbia antisyphilitica Zucc) were collected to isolate, characterize, and identifying plant growth-promoting rhizobacteria (PGPR); 165 rhizobacteria were tested in vitro with Arabidopsis thaliana seedlings to evaluate their potential as plant growth promoters, and obtaining 21 strains with best results in the variables of the number of secondary roots and fresh weight concerning the uninoculated control. Their salinity tolerance was evaluated at concentrations from 0.85 M, 1.7 M and 2.55 M of NaCl. Biochemical tests were accomplishing such as siderophores production, phosphates solubilization, production of Indole-3-acetic acid (IAA), and the activity of the ACC deaminase enzyme. The results obtained from 21 strains selected, high activities were obtained in organic substances like a siderophores since they developed a translucent orange halo around their growth; four rhizobacteria developed a clear halo around the bacterial growth with a thickness between 1.487 mm ± 0.667 mm and 5.267 mm ± 0.704 mm in phosphates solubilization; in the production of Indole-3-acetic acid (IAA), the bacterial strains showed the presence of this phytohormone, with values from 4.444 μg mL-1 to 19.286 μg mL-1; and according to the activity of the ACC deaminase enzyme, values from 0.424 to 1.306 µmol α-KB/h/mg Pr were showed. 16S rRNA sequencing was carried out and genus identified were Bacillus, Staphylococcus, Acinetobacter, Cronobacter and Siccibacter. The results obtained show the potential of the isolated rhizobacteria as growth promoters and the increase in the biomass of the Arabidopsis thaliana seedlings is evident. This is a first indication to proceed to carry out tests in different phenological stages in crops of agricultural importance.

Highlights

The rhizosphere is the area determined between the roots of the plant and the soil that surrounds it (Dijkstra et al, 2014), which is subdivided into three areas: Ectorhizosphere, rhizoplane, and endorhizosphere (Johansson et al, 2004)
We can observe that the area of the Sierra Mojada vs the Viesca area, showed numerical differences in the microorganisms isolated from the Chrome Azurol S (CAS) medium, numerically favoring the area of Viesca. Another appreciation was with those developed on the Luria Bertani (LB) medium, where at the ectorhizophere level, the Sierra Mojada area stood out numerically; the opposite occurred in the NFb medium where the Viesca area the values of ectorizospheric microorganisms were higher than those of the Sierra Mojada area (Figure 2ab)
In accordance with the above and knowing the classification of halophilic microorganisms with respect to their salt requirement, it is possible to confirm that the strains isolated in this study belong to the group of moderately halophilic bacteria, since they can tolerate a wide range of salt concentrations

Summary

Introduction

The rhizosphere is the area determined between the roots of the plant and the soil that surrounds it (Dijkstra et al, 2014), which is subdivided into three areas: Ectorhizosphere, rhizoplane, and endorhizosphere (Johansson et al, 2004). Rhizobacteria have various mechanisms to promote plant growth, including an increase in nutrient mobilization, nitrogen fixation, improved nutrient absorption, and biological control of pathogens (Bais et al, 2006; De-Bashan et al, 2007; Dias et al, 2009; Hariprasad and Niranjana, 2009; Altomare and Tringovska, 2011) They synthesize growth-regulating substances such as gibberellins, cytokinins, and auxins, they stimulate the density and length of root hairs, thereby increasing the absorption capacity of water and nutrients, which results in greater growth and adaptation to conditions of drought, acidity, and alkalinity (Sandhya et al, 2010; Saraf et al, 2011). Some rhizobacteria have antagonistic results on other microorganisms and induce systemic resistance in plants (Sharma et al, 2007)

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