Trichoderma atroviride SC1 (SC1) was isolated from hazelnut wood and it is effective in the biocontrol of soil-borne pathogens. However, its effectiveness decreases as its population declines in the soil over time. To improve its persistency in the soil, lignocellulosic materials (wood pellets) were tested to be used as carriers to sustain the population of SC1 and facilitate its incorporation into the soil. A method was developed to coat wood pellets of fir, beech, and chestnut with a conidial suspension to reach a preset concentration (i.e. 10^4, 10^5, and 10^6 cfu/ g of wood). The growth of SC1 on each type of wood was compared. Chestnut pellets were excluded from further experiments because they had low counts of colony-forming units (cfu) of SC1. Beech pellets were preferred over fir pellets for showing more suitable physicochemical characteristics for soil application. In addition, for the same wood type, increased initial coating concentrations did not impact the final colony counts of SC1 and no significant difference was observed between the counts of 10^4, 10^5, and 10^6 cfu/g of wood at the end of the experiment. The addition of small quantities of nitrogen increased the final cfu on all types of wood pellets. The growth of SC1 on beech pellets was then tested by adding cheap nitrogen sources namely, soy flour, soy protein isolates, and proteins that originated from animal wastes. The best results were obtained with soy protein isolates (1 g/L) and the population of SC1 reached 10^9 cfu/ g of beech wood. Finally, this carrier of coated beech pellets with soy protein isolates was tested in the soil under controlled conditions, in an experimental greenhouse at 25°C and 60% of soil humidity. The pellets were coated to reach a final concentration of 5×10^5 cfu/ g of beech and 10 g of beech coated pellets were mixed with 1 kg of soil in plastic pots to reach the final concentration of 5×10^3 cfu/ g of soil. The carrier increased the bacterial richness and diversity of the soil and decreased the fungal ones. The total Trichoderma population persisted in the first month and then declined after three months with competition from other bacteria such as Massilia spp. and fungi such as Stachybotrys spp. and Mortierella spp.

Bacterial endophytes are the organisms that live inside the plant for a full or a part of their life cycle. Endophytic bacteria have captured the interest of agriculture industry due to their plant beneficial properties, such as synthesis of phytohormones, solubilization of soil nutrients, and alleviation of biotic and abiotic stresses. Several studies have reported that stress tolerant endophytic bacteria can work with a similar performance as non-stressed conditions when inoculated to the plants under stressed conditions. Combination of abiotic stresses such as salinity, drought and low nitrogen stress can have additive or agonistic effects on bacterial and plant growth, and their interactions. However, very few studies have reported the impact of combined stress on endophytic bacterial assisted plant growth promotion. Therefore, understanding the underlying mechanisms of endophytic bacterial assisted plant’s tolerance abiotic stresses may provide the means of better exploiting the beneficial abilities of endophytic bacteria in agricultural production. Thus, the aim of this thesis was to study the stress tolerance mechanisms, beneficial characteristics, and plant growth promotion characteristics of endophytic bacteria under individual and combined abiotic stresses. Transcriptome analysis of endophytic bacteria revealed that tolerance mechanisms to deal with one kind of stress is different than concurrent stresses. Salinity and drought stress largely modulated the genes involved in flagellar assembly and membrane transport, showing reduced motility under stress conditions to preserve the energy. Additionally, bacterial endophyte that can fix nitrogen was studied with maize plant growth promotion under drought and low nitrogen stress conditions. The results suggested that diazotrophic bacterial endophyte can promote plant growth under moderate individual and combined stress conditions. Plant growth promoting endophytic bacteria can be utilized as an efficient tool to increase crop production under individual and concurrent abiotic stresses.