Characterization of Plant Growth-Promoting Traits and Inoculation Effects on Triticum durum of Actinomycetes Isolates under Salt Stress Conditions

Rihab Djebaili,Mahmoud Kitouni,Maria Smati,Maddalena Del Gallo,Massimiliano Rossi,Cinzia Forni,Marika Pellegrini

doi:10.3390/soilsystems5020026

Rihab Djebaili, Mahmoud Kitouni + Show 5 more

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https://doi.org/10.3390/soilsystems5020026

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Abstract

This study aimed to characterize the halotolerant capability, in vitro, of selected actinomycetes strains and to evaluate their competence in promoting halo stress tolerance in durum wheat in a greenhouse experiment. Fourteen isolates were tested for phosphate solubilization, indole acetic acid, hydrocyanic acid, and ammonia production under different salt concentrations (i.e., 0, 0.25, 0.5, 0.75, 1, 1.25, and 1.5 M NaCl). The presence of 1-aminocyclopropane-1-carboxylate deaminase activity was also investigated. Salinity tolerance was evaluated in durum wheat through plant growth and development parameters: shoot and root length, dry and ash-free dry weight, and the total chlorophyll content, as well as proline accumulation. In vitro assays have shown that the strains can solubilize inorganic phosphate and produce indole acetic acid, hydrocyanic acid, and ammonia under different salt concentrations. Most of the strains (86%) had 1-aminocyclopropane-1-carboxylate deaminase activity, with significant amounts of α-ketobutyric acid. In the greenhouse experiment, inoculation with actinomycetes strains improved the morpho-biochemical parameters of durum wheat plants, which also recorded significantly higher content of chlorophylls and proline than those uninoculated, both under normal and stressed conditions. Our results suggest that inoculation of halotolerant actinomycetes can mitigate the negative effects of salt stress and allow normal growth and development of durum wheat plants.

Highlights

Agriculture is affected by climate change, excessive uses of chemicals, exploitation of groundwater in areas close to the sea, and insufficient drainage, which increased soil exposure to salt stress [1]
Proline (Sigma) was used as reference standard (y = 0.0314x + 0.0409; R2 = 0.9993) and the results were expressed as μg proline g fresh weight−1
Halotolerant/halophilic plant growth-promoting (PGP) bacteria are physiologically adapted to environmental changes and increase plant tolerance to salinity thanks to several PGP traits [52]

Summary

Introduction

Agriculture is affected by climate change, excessive uses of chemicals, exploitation of groundwater in areas close to the sea, and insufficient drainage, which increased soil exposure to salt stress [1]. Salinity is a major problem affecting agricultural productivity, especially in arid and semi-arid soils [1,2,3,4,5]. Salinity degrades soil fertility and interferes with the normal development of plants, severely affecting crop productivity [3,6,7]. The decrease in the acquisition of nutrients and the accumulation of Na+ ions [9] causes osmotic stress and closure of the stomata, which reduces the leaf water level and alters CO2 uptake and photosynthesis [4,10]. The decrease in water status due to salinity alters photosynthesis causing the generation of reactive oxygen species (ROS) [11,12]

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