Ethylene is a plant growth regulator and stress hormone (Mayak et al., 2004b; Pierik et al., 2007) that is produced by almost all plant species. This gaseous growth hormone has a key role in causing physiological changes in plants at the molecular level. The production of ethylene is significantly enhanced in response to environmental stresses such as drought and salinity. Excessive ethylene inhibits root growth and, as a consequence, limits further growth of the plant. High ethylene levels in nodules is also associated with decreased N₂ fixation (Ma et al., 2002). Although ethylene production near roots is constantly modulated during plant growth and development (Mayak et al., 2004a; Mahajan and Tuteja, 2005; Gamalero and Glick, 2015), reducing stress-induced ethylene levels alleviates some effects of stress on plants (Glick, 2004; Etesami and Beattie, 2017).

As described earlier, PGPRs that secrete the enzyme ACC deaminase can reduce ethylene levels by metabolizing ACC, a precursor of plant-produced ethylene, into α-ketobutyrate and ammonia (Etesami and Beattie, 2017). Plants inoculated with ACC deaminase-producing PGPRs often exhibit extended root growth, attributed to reductions in ethylene, and enhanced resistance to salinity stress (Mayak et al., 2004a,b; Cheng et al., 2007; Glick et al., 2007; Zahir et al., 2009; Nadeem et al., 2010; Barnawal et al., 2012; Jha et al., 2012; Etesami and Beattie, 2017). These PGPRs can also influence plant ethylene homeostasis by altering the expression of genes encoding the ethylene synthesis enzymes ACC synthase and ACC oxidase (Tsukanova et al., 2017).

Although salinity has been associated with the loss in ACC deaminase production by some PGPRs (Upadhyay et al., 2009), at least some salt-tolerant PGPRs isolated from saline environments appear to maintain ACC deaminase production based on documentation of their beneficial properties in helping plants overcome salinity stress by reducing ethylene levels (Mayak et al., 2004a). For example, 25 out of 140 halotolerant bacterial isolates from coastal soils of the South Korean Yellow Sea showed ACC deaminase activity (Siddikee et al., 2010); these bacterial isolates belonged to the genera of Arthrobacter, Bacillus, Brevibacterium, Corynebacterium, Exiguobacterium, Halomonas, Micrococcus, Oceanimonas, Planococcus, and Zhihengliuella. ACC deaminase-producing PGPRs isolated from saline environments alleviated salinity stress in a variety of plants. For example, the ACC deaminase-producing PGPR strains P. fluorescens N3 and P. putida Q7 promoted the growth of maize roots by 3.3-fold, and maize shoots by 2.3-fold, respectively, under salinity stress as compared to un-inoculated controls (Kausar and Shahzad, 2006; Khan et al., 2016). Similarly, inoculation of legume plants with ACC deaminase-producing rhizobia isolated from saline soils promoted nodule formation (Shaharoona et al., 2006), and inoculation of wheat plants with the PGPR strain A. brasilense FP2 from saline soils resulted in a decrease in the expression of the plant ACC oxidase (Camilios-Neto et al., 2014).

In addition to halotolerant bacteria isolated from saline environments, halotolerant bacteria isolated from various halophytic species exhibit ACC deaminase production (Table 1; Siddikee et al., 2010; Jha et al., 2012; Zhou et al., 2017). ACC deaminase-producing PGPRs isolated from halophytes have been found to alleviate salinity stress and increase plant growth for both halophytes and salinity-sensitive crop plants (Table 1). For example, novel diazotrophic halotolerant bacteria isolated from the roots of Salicornia brachiata featured ACC deaminase activity and these isolates included Brachybacterium saurashtrense, Brevibacteriumcasei, Cronobacter sakazakii, Haererehalobacter, Halomonas, Mesorhizobium, Pseudomonas, Rhizobium radiobacter, Vibrio, and Zhihengliuella (Jha et al., 2012). Moreover, growth parameters of S. brachiate increased significantly under salt stress after re-inoculation with B. saurashtrense and Pseudomonas (Jha et al., 2012). In another study (El-Tarabily and Youssef, 2010), one out of 62 bacterial isolates from the A. marina rhizosphere exhibited a high level of ACC deaminase activity. Following inoculation of this isolate, identified as P. maricaloris, plant seedlings exhibited a decrease in the endogenous levels of ACC and improved growth undersalinity stress. Following the inoculation of red pepper plants with the ACC deaminase-producing halotolerant PGPRs Brevibacterium iodinum, Zhihengliuela alba, and Bacillus licheniformis isolated from halophytes, ethylene levels in the plants decreased by 44, 53, and 57%, respectively. Furthermore, their salt tolerance, as assessed using a salt tolerance index, increased significantly compared to non-inoculated plants (Siddikee et al., 2011). These studies illustrate that habitat-adapted ACC deaminase-producing PGPRs associated with halophytes can mitigate the effects of salinity stress on crops and reduce ethylene to below growth-inhibitory levels (Jha et al., 2012).

Considerable attention has been given to the isolation of ACC deaminase-producing salt-tolerant PGPRs for their use in promoting plant growth in saline environments (Hardoim et al., 2008; Nadeem et al., 2010; Ali et al., 2014). Methods of isolating such PGPRs are well-established (Penrose and Glick, 2003). A rapid and efficient approach to their isolation is using polymerase chain reaction (PCR)-based screening for the ACC deaminase-encoding gene acdS coupled to a colorimetric ninhydrin assay to measure ACC (Nikolic et al., 2011; Jasim et al., 2015; Li et al., 2015b; Qin et al., 2016). Interestingly, recent results suggest that endophytic bacteria are more able to produce the enzyme ACC deaminase than PGPRs isolated from other habitats, including the surfaces of leaves and roots and from non-rhizosphere soil (Bruto et al., 2014; Qin et al., 2016). Future research that compares the bio-activity of ACC deaminase-producing bacteria isolated from various habitats, including distinct tissues of halophytic plants, would be useful.

Phytohormones regulate the protective response of plants to biotic and abiotic stresses (Raghavan et al., 2006), and also the development and tolerance to diverse environmental stresses including salinity stress (Ryu and Cho, 2015). Plant responses to salt stress include an array of changes at the molecular, biochemical, and physiological levels (Manchanda and Garg, 2008; Ahmad et al., 2013; Kumari et al., 2015), and depend upon environmental conditions, soil properties, and plant growth stage (Zhu et al., 1992). Previous studies (Dodd and Pérez-Alfocea, 2012; Khan et al., 2016) indicate that salinity can either diminish (300 mM NaCl) (Dunlap and Binzel, 1996) or increase (100 mM NaCl) (Albacete et al., 2008) endogenous IAA levels in roots. Plants can also respond to exogenous phytohormones, and these can relieve the adverse effects of salinity (Singh and Jain, 1982; Zahir et al., 2010). Thus, exogenous application of phytohormones and their precursors provides an attractive approach to counter salt stress conditions by changing the balance of endogenous levels of hormones (Ilangumaran and Smith, 2017). This was illustrated in a study showing that treating wheat seeds with IAA reduced the detrimental effects of salinity stress on wheat growth (Datta et al., 1997). In addition to stimulating root proliferation, which can enhance growth and salt tolerance (Dodd and Pérez-Alfocea, 2012), IAA can help maintain leaf growth, which helps prevent salinity-induced limitations in plant productivity (Munns, 2002; Albacete et al., 2008). IAA has also been reported to enhance the protection of bacterial cells against abiotic stresses such as high salt concentrations (Bianco et al., 2006).

PGPRs may enhance plant growth, in part, by modulating the plant hormonal balance (Ilangumaran and Smith, 2017; Tsukanova et al., 2017). IAA production is a relatively common trait of most salt-tolerant PGPRs (Dodd et al., 2010), and IAA-producing PGPRs can increase the fitness of plants grown in salt-affected soils (Tiwari et al., 2011). PGPRs may improve crop salt tolerance by altering hormonal root–shoot signaling (Yang et al., 2009). The ability to modify plant stress levels by providing IAA, which influences the development of lateral roots, has previously been reported for halotolerant-bacteria isolated from coastal soils (Siddikee et al., 2010), halophyte roots in Argentina (Sgroy et al., 2009), highly saline habitats (Tiwari et al., 2011), the halophyte Prosopis strombulifera (Piccoli et al., 2011), the rhizosphere of halophytic weeds from the Pakistani Khewra salt range (Naz et al., 2009), halotolerant plants from a Chinese coastal sandbank (Bian et al., 2011), and the rhizosphere of C. annum growing in desert areas (Marasco et al., 2012). Some IAA-producing salt-tolerant PGPRs isolated from halophytes are shown in Table 1, as is their potential as a tool for promoting the salt tolerance of halophytes and glycophytes. For example, Tiwari et al. (2011) demonstrated that inoculation of wheat with IAA-producing salt-tolerant Halomonas sp. resulted in a higher IAA content in the rhizosphere of treated plants than control plants and increased plant growth. In another study, the IAA-overproducing strain Sinorhizobium meliloti ameliorated the reduced growth of Medicago truncatula in saline soils (Bianco and Defez, 2009). This work was further supported by Egamberdieva (2009). These studies clearly show that managing IAA production in halophytic and non-halophytic plants by endophytic and rhizosphere bacteria may be an important tool in conferring salt tolerance.

Cytokinins (CKs) are also involved in the development of plant resistance to biotic and abiotic stresses (Großkinsky et al., 2011; O'Brien and Benková, 2013). CK production is a relatively common trait of PGPRs (Dodd et al., 2010). PGPRs can influence plant CK concentration by synthesizing CK or altering CK homeostasis in the plant (Arshad and Frankenberger, 1991; de Garcia Salamone et al., 2005; Glick, 2012; Pallai et al., 2012; Kapoor and Kaur, 2016). The Platycladus orientalis plants inoculated with a CK-producing PGPR strain B. subtilis had increased CK levels in the shoots and were more resistant to drought (Liu et al., 2013). Increased growth of drought-stressed lettuce plants inoculated with a CK-producing B. subtilis strain suggested modulation of root-to-shoot CK signaling (Arkhipova et al., 2007). The ability of PGPRs to synthesize CK or alter plant CK homeostasis highlights the importance of understanding how PGPRs stimulate growth and increase plant resistance to salinity.

Gibberellic acid (GA) positively regulates cell division and elongation, hypocotyl and stem growth, and leaf and root meristem size (Guo et al., 2015; Wang et al., 2015; Martínez et al., 2016). GA signaling is a key factor in the inhibition of plant growth under stress (Magome and Kamiya, 2016; Martínez et al., 2016). PGPRs can influence the endogenous GA levels in plants (Bottini et al., 2004; Kang et al., 2014a; Shahzad et al., 2016). Some PGPR strains, such as B. amyloliquefaciens RWL-1, Promicromonospora sp. SE188, Leifsonia soli SE134, and Enterococcus faecium LKE12, can synthesize GA (Bottini et al., 2004; Kang et al., 2012, 2014a; Lee et al., 2015; Shahzad et al., 2016). After inoculation of plants with the GA-producing PGPR strains, B. cereus MJ-1 (Joo et al., 2005) and Promicromonospora sp. SE188, the amount of endogenous GA in the shoots increased (Kang et al., 2014a). Some bacterial isolates from the halophyte P. strombulifera (Piccoli et al., 2011) and the rhizosphere of halophytic weeds from the Pakistani Khewra salt range showed the ability to produce GA (Naz et al., 2009), as did the PGPR strains B. licheniformis, Lysinibacillus fusiformis, Achromobacter xylosoxidans, and Brevibacterium halotolerans isolated from the halophyte P. strombulifera (Sgroy et al., 2009).

Abscisic acid (ABA) is an important plant stress hormone that is synthesized in response to abiotic stresses and activates the genes responsible for stress resistance (Sah et al., 2016). This hormone plays an important role in alleviating salinity stress by mediating stomatal, and thereby photosynthetic, responses to high salinity (Dodd and Pérez-Alfocea, 2012). It also plays a crucial role in plant-PGPR interactions (Dodd, 2003). Many PGPRs produce ABA in vitro (Dodd et al., 2010); these include A. brasilense, B. licheniformis, Novosphingobium sp., P. fluorescens, Rhodococcus sp. P1Y, and Variovorax paradoxus (Sgroy et al., 2009; Jiang et al., 2012; Belimov et al., 2014; Salomon et al., 2014; Cohen et al., 2015). PGPRs can also produce ABA under salinity stress conditions and increase growth of salinized plants (Naz et al., 2009). For example, in a study, following inoculation of plants with ABA-producing strains such as B. licheniformis Rt4M10, P. fluorescens Rt6M10, A. brasilense Sp 245, the internal ABA content increased and inoculated plants become more resistant to drought compared to un-inoculated plants (Salomon et al., 2014; Cohen et al., 2015). In addition, inoculation with ABA-producing PGPRs often decreased the accumulation and concentration of ABA in roots and significantly altered the long-distance signaling of shoot-to-root ABA transport in the phloem and the root-to-shoot ABA transport in the xylem (Dodd and Pérez-Alfocea, 2012; Jiang et al., 2012; Belimov et al., 2014; Qin et al., 2016); the resulting changes in ABA levels may mitigate the plant's sensitivity to water scarcity. Recently, the two rhizospheric bacteria Rhodococcus sp. and Novosphingobium sp. were found to metabolize ABA in vitro (Belimov et al., 2014; Qin et al., 2016), suggesting a mechanism for decreasing plant ABA concentrations. Interestingly, disrupting plant ABA homeostasis can influence the activity of halotolerant PGPRs, as shown by wild-type tomato plants that exhibited enhanced growth, and ABA-deficient mutant plants that exhibited reduced growth, in response to B. megaterium inoculation (Porcel et al., 2014; Qin et al., 2016). Collectively, these results suggest that ABA-producing halotolerant PGPRs, ABA-metabolizing halotolerant PGPRs, and general halotolerant PGPRs will act differently in adjusting plant ABA status and thus may result in variable plant responses to salinity stress. ABA production has also been reported in bacterial isolates from halophytes, including from the rhizosphere of halophytic weeds from the salt range of Pakistani Khewra (Naz et al., 2009) and the halophyte P. strombulifera (Piccoli et al., 2011). L. fusiformis, B. subtilis, B. halotolerans, B. licheniformis, B. pumilus, A. xylosoxidans, and Pseudomonas putida are some ABA-producing bacteria isolated from the halophyte P. strombulifera (Sgroy et al., 2009). Relatively little is known of the role of ABA in plant-bacterial interactions. The ability of PGPRs to alter ABA levels in plants suggest opportunities to use these bacteria to influence plant growth and abiotic stress resistance, and highlights a need for more research to understand how PGPRs influence plant ABA signal transduction components.

Jasmonic acid (JA) is also involved in abiotic stress resistance (Ahmad et al., 2016). Several endophytic PGPRs synthesize JA and salicylic acid (SA) (Forchetti et al., 2007; Chen et al., 2014). Inoculating plants with the PGPR strains P. fluorescens Pf4, P. aeruginosa Pag (Singh et al., 2003), and B. amyloliquefaciens LJ02 (Li et al., 2015a) resulted in a rise in the endogenous levels of SA in various plant tissues. Inoculation of Vitis vinifera with the PGPR strain Burkholderia phytofirmans PsJN also led to SA accumulation (Bordiec et al., 2010), as did inoculation with the GA-producing PGPR strains Promicromonospora sp. SE188 (Kang et al., 2012) and B. amyloliquefaciens RWL-1 (Shahzad et al., 2016).

Although there is some evidence that PGPRs improved plant salt tolerance by altering the endogenous hormone status (Kang et al., 2014b; Sahoo et al., 2014; Qin et al., 2016; Ilangumaran and Smith, 2017), little is known about how PGPRs influence this process. We have a similar knowledge deficit regarding the potential for halotolerant PGPRs to synthesize many of these phytohormones and to produce them in vitro or in planta. Bacterial isolates from halophytes have thus far been screened primarily for IAA synthesis, among the hormones discussed. However, the roles of GA, ABA, CK, SA, and JA in the physiology of plant halotolerance indicates that future research on how bacterial isolates from halophytes influence phytohormone homeostasis in plants may be fruitful.

Phosphorus is one of the major essential macronutrients for plants. Although organic and inorganic P are abundant in soils, P availability is limited due to its presence in insoluble forms. Whereas, P comprises about 0.05% (w/w) of soils, often only 0.1% of the total P is available to plants because of poor solubility and its fixation in soil (Goldstein, 1986). In both saline soil-based and fertile soil-based agriculture, intensive cultivation strongly depletes soil nutrients. The use of inorganic NPK fertilizers increases soil salinity, particularly when coupled with saline irrigation. Phosphate-solubilizing halotolerant PGPRs provide an opportunity to enhance P availability to plants without exacerbating soil salinity levels. Phosphate-solubilizing PGPRs can solubilize insoluble phosphates via various mechanisms like chelation, ion exchange, and acidification by secreting low molecular weight organic acids (Sharma et al., 2013; Etesami, 2018). In salt-affected soils, inoculation with phosphate-solubilizing halotolerant PGPRs improved plant growth and suppressed the adverse effects of salt (Giri et al., 2004). Following the inoculation of Solanum lycopersicum plants with Achromobacter piechaudii, plant P content and water use efficiency increased under salinity stress (Mayak et al., 2004a). Similarly, inoculation of wheat with B. aquimaris increased plant P content under salinity stress in the field (Upadhyay and Singh, 2015). Both studies suggest that phosphate-solubilizing PGPRs solubilize insoluble P in saline soils. Halotolerant bacteria isolated from halophytes also exhibit P solubilization activity (Table 1). A screen of the mangrove A. marina rhizosphere identified 129 bacterial strains with the ability to solubilize rock phosphate, with Oceanobacillus picturae able to mobilize 97% of this mineral (El-Tarabily and Youssef, 2010). Bacteria isolated from halophytes, including Arthrobacter, Bacillus, Azospirillum, Vibrio, Phyllobacterium, and O. picturae, were shown to solubilize Ca₃(PO4)₂, AlPO₄, and FePO₄ (Bashan et al., 2000; Banerjee et al., 2010; El-Tarabily and Youssef, 2010; Yasmin and Bano, 2011) and increase the P content in both halophytes and glycophytes under salinity stress (Table 1). When the halophytes S. bigelovii and S. bigelovii were inoculated with various halotolerant PGPRs, including Azospirillum, Vibrio, Bacillus, and Phyllobacterium, the P content of the foliage increased (Bashan et al., 2000). This increased P content in plant tissues may help ameliorate the growth-restraining effects of salinity.

Iron is a micronutrient that is a component of many enzymes involved in biochemical processes, including respiration, photosynthesis, and N₂ fixation (Kobayashi and Nishizawa, 2012; Abbas et al., 2015). Iron availability is very low in calcareous and saline sodic soils throughout the world (Rabhi et al., 2007; Abbas et al., 2015). These soils suppress the availability of most micronutrients, including iron, and suppress plant growth by concurrent salinity and iron deficiency stresses (Yousfi et al., 2007; Abbas et al., 2015). PGPRs often secrete siderophores, which are small, high-affinity Fe(III)-chelating compounds that scavenge iron, and the iron–siderophore complexes can be easily accessed by plants (Kloepper et al., 1980). Siderophore production by halotolerant PGPRs isolated from halophytes has been reported (Table 1); however, the ability of these strains to increase the availability of iron and other micro-elements, such as Zn, Mn, and Cu, to plants is not yet known.

Most agricultural systems depend on the application of exogenous nitrogen, as it is often the nutrient that most limits productivity (Vitousek and Howarth, 1991). The productivity of halophytic crop species can also be limited by a lack of available N in saline soils. For legumes, nitrogen fixation is more sensitive than plant growth to soil salinity (Djekoun and Planchon, 1991), and all stages in nodule formation and nodule function are negatively affected by salinity (de la Peña and Pueyo, 2012; Bruning and Rozema, 2013). Salinity can interfere with plant N nutrition and thus decrease the N content of plant tissues (Naidoo, 1987), as illustrated by salinity-mediated repression of ammonium and nitrate uptake and assimilation (Ullrich, 2002). Typically, farmers use chemical fertilizers to compensate for a lack of soil N; however, the excessive use of inorganic fertilizers may increase salinity, severely degrade the soil structure, and change the composition of the soil microflora (Akhavan-Kharazian et al., 1991; Rueda-Puente et al., 2003). Salinity also results in low soil microbial activity due to osmotic stress and ion toxicity. Increases in soil salinity in many parts of the world are therefore limiting plant productivity and the benefits accrued from biological N₂ fixation (Jha et al., 2012). Salt-tolerant N₂-fixing PGPRs can tolerate osmotic stress by producing osmolytes that allow them to maintain their cell turgor and metabolism (Yan et al., 2015). N₂ fixation by salt-tolerant bacteria associated with the roots of halophytes is an important source of available N in saline soils. Furthermore, these roots are a source of halotolerant N₂-fixing bacteria with plant growth-promoting potential (Table 1; Rueda-Puente et al., 2003; Jha et al., 2012; Sharma et al., 2016), some of which have been found to increase the growth of halophytes as well as non-halophytic crops in saline soils (Table 1). The potential benefits of biological N₂-fixers to halophytes and salt-sensitive crops (Rueda-Puente et al., 2003; Jha et al., 2012) highlight the interest in exploring N₂-fixing halotolerant PGPRs as potential bio-fertilizer resources for saline soil-based agriculture.

In addition to disrupting plant physiology and morphology, soil salinity increases plant susceptibility to pathogens (Besri, 1993). Plant diseases are a major constraint to crop yields but can potentially be controlled biologically by using PGPRs. Biological control using PGPRs offers a more eco-friendly approach to disease management than agricultural chemicals (Compant et al., 2010; Etesami and Alikhani, 2018). Some mechanisms that PGPRs use to counter the deleterious effects of phytopathogens include (Olanrewaju et al., 2017): (i) the synthesis of one or more antimicrobial metabolites (Couillerot et al., 2009), many of which have been reported in PGPRs of the genera Bacillus and Pseudomonas. These metabolites may serve as cytotoxic, antifungal, antibacterial, phytotoxic, antihelminthic, antiviral, antioxidant, and/or antitumor agents (Olanrewaju et al., 2017); (ii) the production of fungal cell wall-degrading enzymes (Chernin et al., 1995) such as lipase, which can degrade some fungal cell wall-associated lipids, β-1,3-glucanase, which can degrade cell wall carbohydrates, chitinase, which can degrade the integral fungal cell wall component chitin (Husson et al., 2017), and protease, which can degrade cell wall proteins (Vaddepalli et al., 2017); (iii) competition either for nutrients or for binding sites on plant roots (Barahona et al., 2011); such competition can limit phytopathogen growth or binding to the plant thereby making it difficult for the pathogen to proliferate (Olanrewaju et al., 2017); (iv) the synthesis of hydrogen cyanide, which when produced by bio-control PGPRs such as Rhizobium, Pseudomonas, Alcaligenes, Bacillus, and Aeromonas, inhibits cytochrome C oxidase as well as other important metalloenzymes (Nandi et al., 2017); (v) activation of induced systemic resistance, which is a resistance mechanism in plants (Van Loon et al., 1998; Halfeld-Vieira et al., 2006) in which exposure of plants to specific microbes, such as some biocontrol PGPRs, primes the plant to react faster and more strongly to a subsequent pathogen attack (Olanrewaju et al., 2017). Induction of systemic resistance provides strong protection coordinated by phytohormone signaling pathways (Pieterse et al., 2012, 2014; Walters et al., 2013); (vi) quorum quenching, which is the disruption of signaling among pathogens. This may occur via the production of signal-degrading enzymes such as lactonase, and the subsequent loss of disruption of signaling may minimize pathogen virulence (Olanrewaju et al., 2017); and (vii) synthesis of siderophores (Olanrewaju et al., 2017), which can prevent or reduce pathogen proliferation by reducing the iron available to pathogens (Shen et al., 2013). The siderophores from PGPRs have been found, at least in some cases, to have a higher affinity for Fe³⁺ than the siderophores from fungal pathogens (Kloepper et al., 1980), thus giving the PGPRs a competitive advantage for iron.

Halophilic PGPRs may also provide biological control of phytopathogens. Many can produce antibiotics and antifungal metabolites, as shown in the halophilic bacteria B. subtilis, B. cereus, B. pumilus, B. licheniformis, Halomonas elongate, and Halobacillus halophilus, which antagonize phytopathogenic fungi such as Fusarium sambucinum, F. roseum var. sambucinum, F. oxysporum, F. moniliforme, F. graminearum, Penicillium citrinum, Aspergillus flavus, and Botrytis cinerea; these organisms have been shown to produce antibiotics, proteases, chitinases, and β−1,3-glucanases (Niehaus et al., 1999; Sadfi et al., 2001, 2002; Sadfi-Zouaoui et al., 2008; Essghaier et al., 2009; Siddikee et al., 2010; Berrada et al., 2012; Ruppel et al., 2013; Goswami et al., 2014; Singh and Jha, 2016). For example, the strains B. halotolerans Ps9 and B. pumilus Ps19, which were isolated from the halophyte P. strombulifera, exhibited protease activity and inhibited the growth of the phytopathogenic fungus Alternaria sp. by more than 50%, at least on plates (Sgroy et al., 2009). Similarly, a halotolerant PGPR Pseudomonas sp. strain isolated from the halophyte Suaeda salsa suppressed the growth of the phytopathogenic fungi Fusarium oxysporum f. sp. cucumerinum and F. oxysporum f. sp. conglutinans (Teng et al., 2010). The biological control potential of halophilic bacteria may be correlated with their production of membrane-bound or extracellular hydrolytic enzymes (Sadfi-Zouaoui et al., 2008). Although antagonistic halotolerant PGPRs may provide an ecologically friendly alternative to synthetic fungicides, research is needed to evaluate that antagonistic potential of halotolerant PGPRs against phytopathogens, and the severity of the disease pressure by these pathogens, in saline environments (Sadfi-Zouaoui et al., 2008).

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.