Selected Rhizosphere Bacteria Help Tomato Plants Cope with Combined Phosphorus and Salt Stresses.

Gylaine Vanissa Tchuisseu Tchakounté,Victor Désiré Taffouo,Sascha Patz,Matthias Becker,Beatrice Berger,Silke Ruppel,Henri Fankem

doi:10.3390/microorganisms8111844

Abstract

Plants are often challenged by multiple abiotic stresses simultaneously. The inoculation of beneficial bacteria is known to enhance plant growth under these stresses, such as phosphorus starvation or salt stress. Here, for the first time, we assessed the efficiency of selected beneficial bacterial strains in improving tomato plant growth to better cope with double stresses in salty and P-deficient soil conditions. Six strains of Arthrobacter and Bacillus with different reservoirs of plant growth-promoting traits were tested in vitro for their abilities to tolerate 2–16% (w/v) NaCl concentrations, and shown to retain their motility and phosphate-solubilizing capacity under salt stress conditions. Whether these selected bacteria promote tomato plant growth under combined P and salt stresses was investigated in greenhouse experiments. Bacterial isolates from Cameroonian soils mobilized P from different phosphate sources in shaking culture under both non-saline and saline conditions. They also enhanced plant growth in P-deficient and salt-affected soils by 47–115%, and their PGP effect was even increased in higher salt stress conditions. The results provide valuable information for prospective production of effective bio-fertilizers based on the combined application of local rock phosphate and halotolerant phosphate-solubilizing bacteria. This constitutes a promising strategy to improve plant growth in P-deficient and salt-affected soils.

Highlights

An ever increasing human population, especially in developing countries, leads to the pressing needs to provide food security to upcoming generations [1]
The results provide valuable information for prospective production of effective bio-fertilizers based on the combined application of local rock phosphate and halotolerant phosphate-solubilizing bacteria
We found that selected bacterial strains solubilized P in vitro under normal and saline conditions and in vivo improved tomato plant growth under P stress, and combined P and salt stresses

Summary

Introduction

An ever increasing human population, especially in developing countries, leads to the pressing needs to provide food security to upcoming generations [1]. About 60–70% of phosphate fertilizers applied are either adsorbed to iron, aluminum oxides, or calcium, and are no longer directly available to the plant [4]. This problem is exacerbated by salinity, which is increasing in many agricultural soils, especially in semi-arid and arid regions, where agriculture performs under irrigation [5]. Salinity negatively affects almost all aspects of plant development, including germination, vegetative growth, and reproductive stages. It suppresses P uptake via plant roots [6]. Expensive phosphate fertilizers represent a major outlay for resource-poor farmers in developing countries like Cameroon

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