Coordination between Bradyrhizobium and Pseudomonas alleviates salt stress in soybean through altering root system architecture

Dilfuza Egamberdieva,Stephan Wirth,Dilfuza Jabborova,Leena A Räsänen,Hong Liao

doi:10.1080/17429145.2017.1294212

Abstract

ABSTRACTIt is a well accepted strategy to improve plant salt tolerance through inoculation with beneficial microorganisms. However, its underlying mechanisms still remain unclear. In the present study, hydroponic experiments were conducted to evaluate the effects of Bradyrhizobium japonicum USDA 110 with salt-tolerant Pseudomonas putida TSAU1 on growth, protein content, nitrogen, and phosphorus uptake as well as root system architecture of soybean (Glycine max L.) under salt stress. The results indicated that the combined inoculation with USDA 110 and TSAU1 significantly improved plant growth, nitrogen and phosphorus contents, and contents of soluble leaf proteins under salt stress compared to the inoculation with the symbiont alone or compared to un-inoculated ones. The root architectural traits, like root length, surface area, project area, and root volume; as well as nodulation traits were also significantly increased by co-inoculation with USDA 110 and TSAU1. The plant-growth promoting rhizobacteria (PGPR) P. putida strain TSAU1 could improve the symbiotic interaction between the salt-stressed soybean and B. japonicum USDA 110. In conclusion, inoculation with B. japonicum and salt-tolerant P. putida synergistically improved soybean salt tolerance through altering root system architecture facilitating nitrogen and phosphorus acquisition, and nodule formation.

Highlights

Soil salinity is considered as one of the most serious environmental problems in arid and semi-arid regions that cause economic losses in agriculture (Rozema and Flowers 2008)
It was previously shown that P. putida TSAU1 tolerated up to 800 mM NaCl, and produced auxin hormone indole-3-acetic acid (IAA) in the King’s B agar (KB) medium containing up to 250 mM NaCl (Egamberdieva & Kucharova 2009)
The growth and nodulation of soybean grown in hydroponic conditions was negatively affected by salinity, that is, 50 mM and 75 mM NaCl

Summary

Introduction

Soil salinity is considered as one of the most serious environmental problems in arid and semi-arid regions that cause economic losses in agriculture (Rozema and Flowers 2008). Higher salt concentrations inhibit the growth of main and lateral roots by suppressing cell division and elongation (Zolla et al 2010). It causes a limitation of soil area for the root system to gain access to larger pools of water and nutrients. It has been reported that legumes, especially their symbiotic performance are inhibited by abiotic stress such as drought and salinity (Hashem et al 2016). The number of rhizobial cells colonizing legume roots, nodulation, and the rate of nitrogen fixation are reduced, which result in poor plant growth in salt-affected soils (Latrach et al 2014). Inhibition of nodule formation in leguminous plants under salt stress has been reported which was due to extra ethylene production by plants (Gresshoff et al 2009), and changes in auxin levels in roots (Liu et al 2015)

Methods

Results

Conclusion