Elsevier

Rhizosphere

Volume 16, December 2020, 100255
Rhizosphere

Inoculation of Pseudomonas mutant strains can improve growth of soybean and corn plants in soils under salt stress

https://doi.org/10.1016/j.rhisph.2020.100255Get rights and content

Abstract

In the last decades, the applications of Plant Growth Promoting Rhizobacteria (PGPR) as inoculants for enhancing crops yield under different stress conditions have reached enormous interest. Pseudomonas putida KT2440 is a well-known rhizobacteria capable of colonizing roots of agronomically important crops. This work aims to evaluate three P. putida KT2440 mutants (mus-20, mus-42, and EU206), which have non-biofilm producing and exopolysaccharide overproducing phenotypes, for their potential as PGPR on soybean and corn plants under saline stress. Experimental studies showed that KT2440 and its mutants were effective in three main PGPR properties: solubilization of phosphates and synthesis of indolic compounds and siderophores. Notably, indolic compounds synthesis increased in mus-20 and EU206 strains. Furthermore, all evaluated strains were tolerant to saline stress. Bacterial inoculation of soybean and corn seeds was effective both in vitro and in vivo tests, even at high salt concentrations (80 and 120 mM NaCl). Among mutant bacteria, EU206 strain seems to be the most efficient PGPR by significantly increasing seed germination, shoot and root lengths, and fresh and dry weights of plants compared to non-inoculated controls, in in vivo tests under saline condition, mainly in both corn plants. These results suggest that inoculation with the P. putida KT2440 mutant strains is an appropriate strategy to enhance the growth of soybean and corn plants, so they might be employed for promoting regional crops growth at field scale using natural saline soils.

Section snippets

. Introduction

Currently, soybean and corn crops stand out for being the ones with the greatest territorial expansion and causing the main losses of biodiversity in tropical regions (Phalan et al., 2013). In Argentina, soybean and corn are the two main crops and the largest source of foreign exchange with 17.2 and 9.1 million planted hectares, respectively (Ministry of Agriculture, Livestock, Fishing, 2019). For these reasons, Argentina is the world's third-largest producer of soybean and is positioned among

Microorganisms, chemical, and culture media

Microorganisms used in this work were: P. putida KT2440, wild-type strain, derived from P. putida mt-2 strain (Regenhardt et al., 2002); and the mus-20, mus-42, and EU206 mutants (Martínez-Gil et al., 2013). The four strains were kindly provided by the Department of Environmental Protection, Zaidín Experimental Station, CSIC, Granada, Spain.

Luria-Bertani (LB) medium, used for maintaining the strains and studying the microbial growth, contained (g L−1): NaCl, 5.0; yeast extract, 5.0; casein

Characterization of PGPR traits

In this study, the ability to solubilize phosphates and synthesize indolic compounds and siderophores by the P. putida KT2440 strain and the mus-20, mus-42, and EU206 mutants was assessed (Table 2).

In this study, the presence of phosphate solubilization halos was not visualized for any of the evaluated strains, after 24 h of incubation. However, small halo zones were observed after 72 h. These results indicate that P. putida KT2440 and its mutants would have ability to solubilize P in the PKV

. Discussion

The use of highly saline soils, unsuitable for agriculture, represents a promising solution to improve food production and reduce the exploitation of native forests. In this context, the incorporation of PGPRs can be a useful tool to achieve this goal. Therefore, in the current study, different mutants of P. putida with non-biofilm producing and EPS overproducing phenotypes were tested for their ability to produce indolic compounds, synthesize siderophores, and solubilize phosphate. Besides,

Conclusions

Taken together, these findings suggest that the inoculation with P. putida KT2440 and its mutants could be suitable for improving plant growth promotion in soybean and corn crops, even under saline conditions, as an alternative to chemical fertilizers. Comparing the plant growth promotion effects of the three mutants, the EU206 strain appears to be the most efficient PGPR by significantly increasing seed germination, shoot and root lengths, and fresh and dry weights of plants regarding the

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Authors acknowledge financial support of PICT 2017-2285 and PICT 2018-3552 grants from Fondo para la Investigación Científica y Tecnológica (FONCyT) and PIP 908-15 grant from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). The authors would like to show their gratitude to Dr. Fabián E. López for his assistance during the planning and development of this research work. The authors also acknowledge Eng. M. Carolina Caram di Santo and Biochem. Pharma. Ana M. Zenoff for their

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