Root inoculation with Azotobacter chroococcum 76A enhances tomato plants adaptation to salt stress under low N conditions

Michael James Van Oosten,Giampaolo Raimondi,Valerio Cirillo,Albino Maggio,Silvia Silletti,Emilio Di Stasio,Valeria Ventorino,Olimpia Pepe

doi:10.1186/s12870-018-1411-5

Michael James Van Oosten, Giampaolo Raimondi + Show 6 more

Open Access

https://doi.org/10.1186/s12870-018-1411-5

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Abstract

BackgroundThe emerging roles of rhizobacteria in improving plant nutrition and stress protection have great potential for sustainable use in saline soils. We evaluated the function of the salt-tolerant strain Azotobacter chroococcum 76A as stress protectant in an important horticultural crop, tomato. Specifically we hypothesized that treatment of tomato plants with A. chroococcum 76A could improve plant performance under salinity stress and sub-optimal nutrient regimen.ResultsInoculation of Micro Tom tomato plants with A. chroococcum 76A increased numerous growth parameters and also conferred protective effects under both moderate (50 mM NaCl) and severe (100 mM NaCl) salt stresses. These benefits were mostly observed under reduced nutrient regimen and were less appreciable in optimal nitrogen conditions. Therefore, the efficiency of A. chroococcum 76A was found to be dependent on the nutrient status of the rhizosphere. The expression profiles of LEA genes indicated that A. chroococcum 76A treated plants were more responsive to stress stimuli when compared to untreated controls. However, transcript levels of key nitrogen assimilation genes revealed that the optimal nitrogen regimen, in combination with the strain A. chroococcum 76A, may have saturated plant’s ability to assimilate nitrogen.ConclusionsRoots inoculation with A. chroococcum 76A tomato promoted tomato plant growth, stress tolerance and nutrient assimilation efficiency under moderate and severe salinity. Inoculation with beneficial bacteria such as A. chroococcum 76A may be an ideal solution for low-input systems, where environmental constraints and limited chemical fertilization may affect the potential yield.

Highlights

The emerging roles of rhizobacteria in improving plant nutrition and stress protection have great potential for sustainable use in saline soils
The highest microbial concentration was recovered in the rhizosphere of tomato plants cultivated under sub-optimal nutrient solution (50% standard nutrient solution) regardless of the salt stress applied (Table 1)
These results indicate that higher nutrient concentration and additional nitrogen provided as NH NO with the optimal nutritional regimen did not further improve the number of fruit per plant and it was inhibitory for shoot and fruit growth

Summary

Introduction

The emerging roles of rhizobacteria in improving plant nutrition and stress protection have great potential for sustainable use in saline soils. We hypothesized that treatment of tomato plants with A. chroococcum 76A could improve plant performance under salinity stress and sub-optimal nutrient regimen. Salinity affects more than 20% of global agricultural production and it is predicted to increase in its extent and severity in the coming decades [17]. Salinization occurs through both natural and anthropogenic processes [12]. High concentrations of salt cause both ionic and osmotic stresses. Salinity induces osmotic stress by lowering the soil water potential, increasing the energy required for uptake of water and nutrients. Plants employ numerous strategies to survive and adapt to salt stress including control of sodium transport across the plasma and tonoplast

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