## 1 Introduction  
Date palm (_Phoenix dactylifera_ L.) is a multipurpose crop cultivated for many millennia in arid and semi-arid regions in the world mostly [1]. In Morocco, date palm covers approximately 59,000 hectares with an average production of 111,701 tons fresh of fruits in 2018 [2]. The date palm has great economic importance since it constitutes the pivot of the oasis ecosystem of the Saharan and pre-Saharan regions of Morocco, and it provides not only dates but also various materials intended for handicrafts, construction and energy production [3]. It also provides a local microclimate that promotes the development of several underlying crops, such as forage species [4]. However, date palm growth is often hampered by soil fertility and other environmental limiting factors, such as drought and soil salinity [5; 6; 7; 8].  
Soil salinity is one of the major problems for agriculture mainly in arid and semi-arid regions, which strongly affects plant growth and productivity [9]. High levels of salinity in soils lead to ion toxicity, disturbed Na\({}^{+}\)/K\({}^{+}\) homeostasis and enhanced production of reactive oxygen species (ROS), thereby causing oxidation of membrane lipids, protein and nucleic acids [10], growth inhibition and disruption of photosynthesis activity and productivity [11; 12; 13]. However, plants can remove generated ROS by different defense mechanisms such as the antioxidant system. The antioxidant system includes many enzymes, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and polyphenol oxidase (PPO) [14; 15]. Another protective mechanism to prevent stress damage is the storage and compartmentalization of toxic ions in specific cell compartments [16; 17]. Previous studies already searched for alternatives that could increase these different defense mechanisms in plants under saline conditions. One of these alternatives is the use of biofertilizers including mycorrhizal fungi (AMF), plant growth-promoting rhizobacteria (PGPR) and compost to reduce the harmful effects of salt stress on plants [8; 10; 18].  
AMF usually form symbiotic relationships with many plants to modulate the growth of host plants grown under saline conditions by direct and indirect mechanisms, such as mitigation of ROS and oxidative damage via the mediation of phytohormone synthesis [18; 19], and enhancing the enzymatic and non-enzymatic antioxidant defense system [20; 21]. Besides, the beneficial effects of AMF are linked to nutrient mobilization, such as that of phosphorus and other micronutrients; the use of soil organic matter; and improvements in soil structure [22; 23; 24; 25; 26; 27]. Additionally, PGPR can mitigate the detrimental effects of salt stress by improving plant growth through the production of phytohormones such as indole acetic acid (IAA) [28], and the fixation of atmospheric N [29].  
Furthermore, compost has been used for decades as a soil conditioner in agriculture to improve the supply of organic carbon and enhance the soil storage capacity of water and nutrients, leading to increased photosynthetic activity, yields and stress tolerance of plants [6; 30; 31; 32; 33].  
The innovative approach combining compost from green waste, native PGPR and AMF has recently shown promise for assisting with alfalfa and other cultures to tolerate heavy metals and salt stress [32; 33; 34].  
The objective of this work was to study the effects of compost, PGPR, AMF and their combination on growth, physiological and biochemical parameters of date palm vitroplants (var. Bouffgous) grown under salt stress. The Bouffgous variety from Morocco is a genetically stable variety multiplied by in vitro culture and presents an important economic interest because it is widely cultivated in Morocco, known for its high productivity and excellent date quality. This study aims to investigate the influence of low-dose, easy to produce, local compost in combination with PGPR and native or exotic AMF, on the tolerance of date palm vitroplants to salt stress.