Atlas Journal of Biology 2024, pp. 830–838 https://doi.org/10.5147/ajb.vi.245 A tla s Jo ur na l o f B io lo gy - IS SN 2 15 8- 91 51 . P ub lis he d By A tla s Pu bl is hi ng , L P (w w w .a tla s- pu bl is hi ng .o rg ) Plant Growth Promoting Rhizobacteria (PGPR) Isolated from an Plant Growth Promoting Rhizobacteria (PGPR) Isolated from an Arid Soil in Saudi Arabia Improve Maize GrowthArid Soil in Saudi Arabia Improve Maize Growth Abdelazize Eljiati1*, Yassine Elmaati2, and Hammou Ouchaou2 1 National Centre for Palms & Dates, Al Dahi, Hittin, Riyadh 13512, Saudi Arabia; 2 R&D Department, YALA Laboratory, Yousef Abdul Latif and Sons Agriculture Ltd. (YALA) Company, Qassim, Saudi Arabia Received: February 19, 2024 / Accepted: April 29, 2024 __________________________________________________ * Corresponding author: a.eljiati@gmail.com 830 AbstractAbstract The rhizosphere represents the main source of bacteria com- monly referred to as rhizobacteria. Such beneficial rhizobac- teria with plant-beneficial activities are generally defined as plant growth promoting rhizobacteria (PGPR). The aim of this study was to investigate the ability of native rhizobacteria (PGPR) isolated from an arid soil of date palm in Al-Qassim region, Saudi Arabia, to enhance plants growth. Maize (Zea mays L.) was used as model crop for this research. Maize seedlings roots were inoculated with Bacillus and Entero- bacter bacteria. The seedlings showed significant increases in stem, leaf, and root growth. The maximal shoot lengths were obtained with strain (I2: Bacillus cereus) (95.41 cm) with an increase of 33.45 % compared to uninoculated control seedlings. The three isolates I2: Bacillus cereus, AZS2: Bacillus subtilis and commercial strain AZB: Azospirillum brasilense) caused a highly significant increase in the total number of leaves ranging from 10.9% to 12.7% compared to the unin- oculated controls. Seedlings inoculated with AZS2: Bacillus subtilis strain exhibited the highest aerial dry biomasses with an improvement of more than 85 % (30.76 g) compared with uninoculated control plants and more than 62 % compared to uninoculated NaCl control plants. The inoculation treat- ment with I2: Bacillus cereus strain induced an improvement of more than 65 % (27.44 g) over uninoculated control and more than 45 % over uninoculated NaCl control. The strain This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creative- commons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. AZS2: Bacillus subtilis produced the highest root dry weights, in comparison to other isolates and induced an improvement of 30.17% (26.06 g) compared to uninoculated control plants and 24.09% compared to uninoculated plants (NaCl control). The most effective rhizobacterial treatment in the dry bio- masses of whole seedling (aerial dry biomass and root dry biomass) is AZS2: Bacillus subtilis strain which induced an improvement of 55% (56.83 g) compared to uninoculated plants (control) and 42% compared to uninoculated plants (NaCl control). The most important production of kernels was recorded with AZS2: Bacillus subtilis strain. Therefore, these findings suggested that the use of PGPR strains as inoculant biofertilizers might be beneficial for crop production cultiva- tion especially in arid and semi-arid regions. Keywords:Keywords: Plant growth promoting rhizobacteria (PGPR), Ba- cillus subtilis, Bacillus cereus, Enterobacter ludwigii, inocula- tion, Zea mays L. A tla s Jo ur na l o f B io lo gy - IS SN 2 15 8- 91 51 . P ub lis he d By A tla s Pu bl is hi ng , L P (w w w .a tla s- pu bl is hi ng .o rg ) IntroductionIntroduction Bacteria that can aggressively colonize the rhizosphere or plant roots or both and promote growth and yield of plants are referred to as plant growth promoting rhizobacteria (PGPR) (Kloepper et al., 1989). These rhizosphere bacteria enhance crop growth and yield directly, either by promot- ing nutrition, for example, by phosphate (Hayat et al., 2010; Sharma et al., 2007; Das et al., 2003), and potassium solu- bilization (Wang et al, 2020; Han et al., 2006) and ammonia production (Mukhtar et al., 2020; Ahmad et al., 2008; Joseph et al., 2007) or by synthesizing metabolites with great agri- cultural interest such as plant growth regulators and sidero- phores (Tian et al., 2009; Arkhipova et al., 2005; Barazani et Friedman, 2001). They can also promote growth indirectly, acting as bio-controlling agents for suppression of growth of soil borne phytopathogen microorganisms and as stimula- tor of other beneficial organisms for the plant (Abbasi et al., 2011; Bhattacharyya and Jha, 2011). PGPR improve soil struc- ture and bioremediate polluted soils by sequestering toxic heavy metal and degrading xenobiotic compounds (Ahemad et al., 2012; Braud et al., 2009). Depending on their beneficial roles in the rhizosphere, PGPR have been classified as biofer- tilizers, phytostimulators, rhizoremediators and biopesticides (Martínez-Viveros et al., 2010). Consequently, the application of these beneficial microorganisms as bioinoculants appears as an ecological friendly biotechnological tool (Dimpka et al., 2009) to alleviate detrimental effects of intensive farm- ing practices that are using synthetic fertilizers and pesti- cides without caring about environmental problems and soil health (Elkoca et al., 2010). Numerous laboratory, greenhouse and field studies are available on the screening of PGPR for their multiple plant growth promoting activities (Wang et al, 2020; Gouda et al., 2018; Oteino et al., 2015; Hayat et al., 2010; Joseph et al., 2007) and utilization of PGPR-based products in agricultural crop production systems (Yadav et al., 2017; Cakmakci et al., 2006). These products are mainly applied as seed treatment, soil amendment, or soil drench at the time of sowing or immediately after transplantation, to facilitate bet- ter nutrient uptake, greater production of growth hormone and beneficial phytochemicals in crops leading to higher crops yield and quality (Kloepper et al., 2004). PGPR activity has been reported in strains belonging to a several genera, such as Pseudomonas, Azospirillum, Azotobacter, Klebsiella, Enterobacter, Rhizobium, Bradyrhizobium, Alcaligens, Ar- thobacter, Burkholderia, Bacillus, Serratia and Xanthomonas (Verma et al., 2013; Karnwal 2009; Patten and Glick 1996; Glick, 1995; Kloepper et al., 1989). Pseudomonas and Bacil- lus spp. have been the most studied bacteria for their plant growth promotion (PGP) activity and ability to produce ben- eficial substances (Kejela et al., 2016; Pham et al., 2017). Isola- tion of native strains adapted to the arid environment may contribute to formulation of inoculants suitable for use in lo- cal crops, as they are adapted to the environment and can be, thereby more competent than imported microbial strains. The positive impact of PGPR has been studied in annual crops like wheat (Bashan, 1986), soybeans (Cattelan et al., 1999), beans (Jarak et al., 2012) and corn (Di Salvo et al., 2018; Ullah et al., 2014) in several ways. Therefore, this study was designed to select effective strains from a series of of native rhizobacteria (PGPR) isolated in an arid area soil of date palm in Al-Qassim region, Saudi Arabia, by maize (Zea mays L.) growth promotion assay un- der greenhouse conditions. These native strains are also com- pared with a commercial microbial strain, as a positive con- trol. Therefore, the application of the selected effective PGPR strains as microbial inoculants for crops would significantly promote their sustainable production in arid conditions and reduce the use of inorganic fertilizers and pesticides, which often pollute the environment. Materials and MethodsMaterials and Methods Bacterial InoculantsBacterial Inoculants The rhizobacterial strains (I2: Bacillus cereus, AZS2: Bacillus subtilis, AZA2: Enterobacter ludwigii and PSA1: Enterobacter ludwigii) used in this study were previously isolated from an arid area soil in Qassim province, Saudi Arabia (Elmaati et al., 2020). These bacterial strains were characterized and select- ed based on their plant growth promoting traits, comprising very good phosphate and potassium solubilization and am- monium production. A commercial strain (AZB; Azospirillum brasilense) was used as a positive control to compare it with these native strains. Inoculation of Maize Plants by PGPR StrainsInoculation of Maize Plants by PGPR Strains To prepare the inoculum for each rhizobacterial strain, pure cultures were grown in nutrient agar (R2A Agar medium). Af- ter 48 hours of incubation at 25 °C, a single colony from each strain was transferred into a 200 ml sterilized Erlenmeyer flask, containing sterilized 102 medium broth (= LMG 1089 medium) with the following composition (g L-1): Sucrose, 20.0; Casein hydrolyzate, 16.0; Yeast extract, 8.0; KH2PO4, 4.0; MgSO4 x 7 H2O, 0.30, and grown aerobically for 4-5 days on a rotating shaker (150 rpm) at 32 °C, to obtain a final concen- tration of 109 CFU ml-1. After incubation, bacterial growth is estimated by measuring the absorbance of the culture at 600 nm. To wash the bacteria, bacterial cells were centrifuged at 3000 rpm for 10 min in 15 ml tubes. The supernatant was then discarded and the pellet was washed once with 5 ml of sterile NaCl solution (Physiologic Sterile Water (0.85%)) and finally resuspended in 200 ml of the same solution. Maize (Zea mays L.) was used as the test plant for the inoc- ulation in this experiment. Seeds of a homogeneous variety were surface sterilized to eliminate all kinds of contamination according to the method of Götz et al. (2006): The seeds were immersed for 1 min in ethanol (70%) with gentle agitation. They are then put back into 12% diluted sodium hypochlo- rite solution containing three drops of wetting agent (Tween 20) for 15 minutes. To get rid of the chlorine, the seeds were rinsed several times with sterile distilled water. Sterilized seeds were sown in alveolar plates containing 831 A tla s Jo ur na l o f B io lo gy - IS SN 2 15 8- 91 51 . P ub lis he d By A tla s Pu bl is hi ng , L P (w w w .a tla s- pu bl is hi ng .o rg ) A tla s Jo ur na l o f B io lo gy - IS SN 2 15 8- 91 51 . P ub lis he d By A tla s Pu bl is hi ng , L P (w w w .a tla s- pu bl is hi ng .o rg ) autoclaved (1: 1 v / v) mixture of peat and vermiculite respec- tively. They were then placed in a greenhouse at a natural photoperiod (at a temperature of 28 to 40 °C) and are regu- larly irrigated. Twenty days after germination, the roots of maize seed- lings were dipped into the inocula for 2 h at 25 °C. Control seedlings were divided into two groups; the first is dipped into sterile NaCl solution as the bacteria washing procedure containing this solution, while the second is dipped into ster- ile distilled water. Each treated seedling was planted in a dis- infected and labeled plastic pot (8 L) containing autoclaved (1/1: v / v) mixture of soil and vermiculite respectively. Pots were then placed in a greenhouse at a natural photoperiod (at a temperature of 28 to 40 °C). The experiment was carried out in a completely randomized block design with 5 replica- tions for each treatment. Seedlings were irrigated with 300 ml of well water every two days to maintain at field capacity and received no fertilizers. Estimation of Some Agro Morphological Parameters of PlantsEstimation of Some Agro Morphological Parameters of Plants To evaluate the response to rhizobacterial inoculation, during the experiment, a daily monitoring of the evolution of the growth of the maize plants was done after the applica- tion of the inoculum for a period of 90 days. The height from the collar (size of the aerial part) and the number of leaves are the main growth parameters used in this study. These two growth parameters were measured at the start and every ten days during the 3 months of treatment. Plant height was de- termined by measuring from the plant’s base to the top of the newest fully developed leaf. At the end of the experiment, the shoots and roots of each plant were put in paper bags and dried in an oven at 65°C for 72 hours (Sfairi, 2013) to report the total dry biomass (shoot and root dry biomass). Statistical Data AnalysisStatistical Data Analysis The mean value of each treatment, as well as the corre- sponding standard deviation, were calculated using the data of all the replicates carried out. The data obtained was ana- lyzed statistically using R 3.2.0 and multivariate analyses were performed using R language (Dray & Dufour, 2007; R Develop- ment Core Team, 2011). ResultsResults Effect of Rhizobacterial Inoculation on Shoot LengthEffect of Rhizobacterial Inoculation on Shoot Length The rhizobacterial isolates (AZB, AZS2, I2, PSA1, and AZA2) significantly affected the shoot length of maize seedlings. Re- sults reveal that PGPR promoted an increase in shoot length over un-inoculated (control) (Figure 1 - A and B). The maximal lengths of the maize seedlings were obtained with strain (I2) (95.41 cm) with an increase of 33.45 % compared to un-inoc- ulated (controls). Treatment of maize seedlings with strain (I2) showed a significant increase in shoot length improvement rates compared to other strains including the commercial strain (AZB). There was no significant difference in shoot length between the two controls. Effect of Rhizobacterial Inoculation on Leaf NumbersEffect of Rhizobacterial Inoculation on Leaf Numbers From 1 to 38 days after emergence (Figure 2A), the num- ber of leaves of maize plants increased linearly in all treat- ments. These results were identical for all the rhizobacterial isolates and the controls. However, we noted the beginning of the stability of the number of leaves between the 40th and the last days of the cycle in some plants. The effects of different rhizobacterial isolates were signifi- cant on the total number of leaves of maize, compared with control. Application of AZS2 isolate to maize seedlings re- corded non-significantly higher number of leaves, compared with AZB and I2, and all these three isolates were compara- tively more effective than rest of the isolates and the two un- inoculated control. The three effective isolates caused a high- ly significant increase in the total number of leaves ranging from 10.9% to 12.7% compared to the un-inoculated control. No significant difference was observed between the two iso- lates (PSA1 and AZA2) and the control with NaCl (Figure 2B). 832 Figure 1.Figure 1. (A) Effect of rhizobacterial inoculation on shoot length (B) Height growth of maize seedlings after 50 days of cultivation under the effect of ap- plied rhizobacterial strains. AA BB A tla s Jo ur na l o f B io lo gy - IS SN 2 15 8- 91 51 . P ub lis he d By A tla s Pu bl is hi ng , L P (w w w .a tla s- pu bl is hi ng .o rg ) 833 Effect of Rhizobacterial Inoculation on Leaf DesiccationEffect of Rhizobacterial Inoculation on Leaf Desiccation During the period of evolution of the different foliar levels of the maize seedlings, we noticed that the leaves of the base wither and turn brown, by a yellowing and drying which be- gins with the end of the leaves and extends thereafter, until they dry out completely. The number of dried older leaves was recorded for each plant. At the end of the experiment, the results of the analysis of variance relating to this param- eter show that there is no statistically significant difference between the rhizobacteria and the controls without bacteria (Figure 3). Effect of Rhizobacterial Inoculation on Aerial Dry BiomassEffect of Rhizobacterial Inoculation on Aerial Dry Biomass The analysis of variance relative to the aerial dry biomasses of maize seedling shows that there is a highly significant dif- ference between the different strains and the un-inoculated control and un-inoculated control NaCl control (with a total aerial dry biomass which marked a rate of 16.59 g and 18.88 g respectively). Seedlings inoculated with AZS2 strain exhib- ited the highest aerial dry biomasses with an improvement of more than 85 % (30.76 g) compared with un-inoculated con- trol plants and more than 62 % compared to un-inoculated NaCl control plants. The inoculation treatment with I2 strain induced an improvement of more than 65 % (27.44g) over un-inoculated control and more than 45 % over un-inocu- lated NaCl control. On the other hand, the commercial strain (AZB) showed an improvement of 64.98% (27.37 g) compared to untreated control and 44.97% compared to untreated NaCl control. The others two strains (PSA1 and AZA2) are charac- terized by their lowest significant effect on aerial dry biomass per comparison to the both control plants (control and NaCl control) (up to 38 % increase) (Figure 4). Effect of Rhizobacterial Inoculation on Root Dry BiomassEffect of Rhizobacterial Inoculation on Root Dry Biomass The effect of the five rhizobacterial strains on the root dry biomasses of maize plants is illustrated in (Figure 5A). All the tested strains were significantly improved the root dry bio- masses in comparison with controls (control and NaCl con- trol), which scored a rate of 20.02 g and 21.00 g respectively. The strain AZS2 produced the highest root dry weights, in comparison to other isolates and induced an improvement of 30.17% (26.06 g) compared to un-inoculated plants (control) and 24.09% compared to un-inoculated plants (NaCl con- trol). While, in comparison with controls, the inoculation with strains I2, PSA1 and AZB showed a significant difference with improvement rates ranging from 16.2% to 19.35%. A tla s Jo ur na l o f B io lo gy - IS SN 2 15 8- 91 51 . P ub lis he d By A tla s Pu bl is hi ng , L P (w w w .a tla s- pu bl is hi ng .o rg ) 0 2 4 6 8 10 12 0 20 40 60 80 Le a ve s n u m b e r Days number Control NaCl Control AZA2 (Enterobacter ludwigii) AZB (Azospirillum brasilense) AZS2 (Bacillus subtilis) PSA1 (Enterobacter ludwigii) I2 (Bacillus cereus) AA BB Figure 2.Figure 2. (A) Evolutionary trend of the adjusted mean of the number of maize leaves (B) Effect of rhizobacterial inoculation on leaf numbers. Figure 3.Figure 3. Effect of rhizobacterial inoculation on leaf desiccation. Figure 4.Figure 4. Effect of rhizobacterial inoculation on aerial dry biomass A tla s Jo ur na l o f B io lo gy - IS SN 2 15 8- 91 51 . P ub lis he d By A tla s Pu bl is hi ng , L P (w w w .a tla s- pu bl is hi ng .o rg ) 834 It is observed from the results (Figure 5B) that the rhizo- bacterial strains caused greater increase in root system of maize plants as compared with controls (control and NaCl control). Indeed, the highest root lengths was recorded with the inoculation of AZS2 and I2 strains), in comparison to oth- er strains. Effect of Rhizobacterial Inoculation on Whole Seedling Dry Effect of Rhizobacterial Inoculation on Whole Seedling Dry Biomass Biomass A very highly significant improvement rate in the dry bio- masses of whole seedling (aerial dry biomass and root dry biomass) inoculated with the rhizobacterial strains is record- ed compared to the un-inoculated plants (control and NaCl control), which scored a level of 36.62 g and 39.94 g respec- tively. The most effective rhizobacterial treatment is AZS2 strain which induced an improvement of 55% (56.83 g) com- pared to un-inoculated plants (control) and 42% compared to un-inoculated plants (NaCl control). Analysis of the variance applied to dry biomasses of whole seedling indicated that there was no significant difference between other strains (I2, AZA2, PSA1 and AZB), but they induced an increase for this parameter compared to the un-inoculated control (Figure 6). Effect of Rhizobacterial Inoculation on Kernel Numbers Effect of Rhizobacterial Inoculation on Kernel Numbers All the inoculated treatments proved statistically superior over un-inoculated control in improving number of kernels. No significant difference was observed between the four bac- terial strains AZB, AZS2, I2 and PSA1. However, the most im- portant production of kernels was recorded with AZS2 strain. While total kernels number was significantly increased with these four strains as compared to AZA2 strain and compared to un-inoculated control (Figure 7). DiscussionDiscussion Plant Growth Promoting Rhizobacteria (PGPR) are free- living microbes that live on or around the roots (Kloepper et al., 1989) and promote plant growth and yield (Wu et al., 2005). Native rhizobacteria (PGPR) isolated in arid area soil of date palm in Al-Qassim region, Saudi Arabia, were used in this study to constitute the rhizobacterial inoculum, which was then used to inoculate maize (Zea mays L.) seedlings. These strains exhibited significant plant growth promoting attributes in vitro tests and selected from previous screening experiments (Elmaati 2020). In addition to its nutritional and Figure 5.Figure 5. (A) Effect of rhizobacterial inoculation on root dry biomass (B) Effect of rhizobacterial inoculation on root length of maize seedlings AA BB Figure 6.Figure 6. Effect of rhizobacterial inoculation on whole seedling dry biomass. Figure 7.Figure 7. Effect of rhizobacterial inoculation on kernel numbers. economic importance, maize has been a keystone model or- ganism for basic and applied research in plant biology (Stra- ble and Scanlon, 2009). Overall, the results of the study of the growth of maize seedlings treated with the various rhizobacterial strains en- abled us to conclude that the efficacy of different strains for growth-promoting of maize was variable. Indeed, the investigated PGPR strains in this work showed positive PGP traits. These potentialities seem playing an effective role for the plant in helping it to better absorb nutrients. PGPR have long been known to promote growth when added to seeds, roots or tubers in a wide range of plant species (Kloepper et al., 1980), increasing both growth and yield (Wu et al., 2005) by improving the concentration of nutrients in the host plant (Canbolat et al., 2006). Several studies have reported that inoculation of maize plants with PGPR strains caused significant increase in plant height, plant dry weight, stem diameter, root length and weight, yield, number of leaves and leaf area, and plant nutri- ent uptake of N, P, K, Fe, Zn, Mn and Cu (Yazdani et al., 2009; Jarak et al., 2012; Gholami et al., 2012; Calvo et al., 2017). Ac- cording to our results maize seedlings inoculated by dipping the roots in bacterial suspensions showed a statistically sig- nificant improvement in the growth parameters studied as compared to treatments without inoculation. Interestingly, the plant height, number of leaves, shoot dry weight, root dry weight and kernels number were significantly higher with plants treated with AZS2 strain (Bacillus subtilis) followed by I2 strain (Bacillus cereus) in comparison with un-inoculated control and with other strains including the commercial strain (AZB, Azospirillum brasilense). This is consistent with previous studies, which demonstrated that plant growth- promoting activities of Bacillus spp. are well characterized as evidenced by increased growth of roots, shoots, and leaves as well as enhanced yields. In this context, increased plant height and shoot biomass of Arabidopsis, corn, and tomato under greenhouse conditions have been reported by inocu- lating with four isolated Bacillus strains from rainforest soils (Huang et al., 2015). Results obtained by Hassan (2017) report that B. cereus Tp.1B and B. subtilis Tp.6B strains significantly increased root length and root weight in maize compared to controls. Co-inoculation of Bacillus spp with other PGPR strains reduces phosphorus demand by 50% without affect- ing maize yield (Yazdani et al., 2009). Moreover, Ferreira et al., 2018 reported that Bacillus subtilis promotes positive influ- ence on plant growth of maize plants under normal condi- tions (without salinity). Bacillus subtilis strain was the most effective in promoting nitrogen accumulation and, therefore, increased chlorophyll content in maize (Aquino et al., 2019; Almaghrabi et al. al., 2014). When tomato seeds were treated with Bacillus subtilis (EPC016), a significant increase in seed- ling growth was observed relative to un-inoculated plants (Ramyabharathi et al., 2013). In another study, Tilak and Red- dy (2006) observed a significant increase in grain yield rate of 43.8% in maize plants inoculated with Bacillus cereus. This last strain was found to exhibit the highest nitrogenase activ- ity among 42 different strains of Bacillus spp studied by Am- brosini et al., (2016). In addition, B. cereus and B. megaterium have been reported as organic phosphorus mineralizing bac- teria (Guang Can et al., 2008). The works of Habib et al., (2015, 2016) on rhizobacteria isolated from saline soil and selected for their PGP activities revealed that they showed significant salt tolerance properties. These rhizobacteria were identified as Enterobacter sp. and Bacillus cereus. Our research indicates that significantly lower values of different growth parameters were recorded in maize plants inoculated with Enterobacter ludwigii in comparison to Bacil- lus subtilis and Bacillus cereus. On the other hand, and com- pared to the un-inoculated control plants, Enterobacter lud- wigii had significant positive effects on maize plant growth parameters. Zaballa et al., (2020) found that barley plants inoculated with the Enterobacter ludwigii strain showed im- provement in growth and phosphate uptake compared to the un-inoculated control. Tahir et al., (2013) reported that inoculation of wheat plants with phosphate-solubilizing and phytohormone-producing bacterial strains such as Azospiril- lum, Bacillus and Enterobacter improved growth and yield. Moreover, several studies have demonstrated the effective- ness of inoculating wheat grains with different rhizobacteria on plant growth (Abbasi et al., 2011; Rana et al., 2011; Baner- jee et al., 2010). Numerous studies have highlighted the in- crease in dry matter weight of aerial parts in wheat (Bashan, 1986) and maize (García de Salamone and Döbereiner, 1996; Ullah et al., 2014; Di Salvo et al., 2018). The positive effects of PGPR on the yield and growth of crops such as wheat (Oz- turk et al., 2003; Salanture et al., 2006) maize (Egamberdi- yeva, 2007; Ullah S and B Asghari, 2015; Pereira et al., 2020) soybean (Cattelan et al., 1999) and sugar beet (Cakmakc et al., 2006) have been explained by the ability of these PGPR to fix N2, solubilize phosphate and produce phytohormones. Thus, these rhizobacteria can be considered as an excellent tool for increasing the availability of phosphorus in plants by mineralization of soil organic phosphorus and by solubiliza- tion of phosphate precipitates (Kucey et al., 1989; Pradhan and Sukla, 2006), production of AIA (Chaiharn and Lumyong, 2011; Swain et al., 2007), HCN (Bakker and Schippers, 1987), ammonia (NH3) (Yadav et al., 2010) and siderophores (Boo- pathi and Rao, 1999). In general, our study clearly showed that the inoculation of maize plants with the rhizobacterial strains significantly promoted maize plants growth. These results suggest that these PGPR strains can be applied as biofertilizers for im- proving plants production. Furthermore, their use can be an ecological alternative to reduce the dependence on chemical fertilizers. ConclusionConclusion The rhizobacterial strains investigated in our study showed their plant growth ability. These native strains, which belong to the genera Bacillus and Enterobacter, significantly enhanced the growth of maize plants when compared with the un-inoculated control plants. The maximal lengths of the maize seedlings were obtained A tla s Jo ur na l o f B io lo gy - IS SN 2 15 8- 91 51 . P ub lis he d By A tla s Pu bl is hi ng , L P (w w w .a tla s- pu bl is hi ng .o rg ) A tla s Jo ur na l o f B io lo gy - IS SN 2 15 8- 91 51 . P ub lis he d By A tla s Pu bl is hi ng , L P (w w w .a tla s- pu bl is hi ng .o rg ) 835 with strain (I2: Bacillus cereus) (95.41 cm) with an increase of 33.45 % compared to un-inoculated (controls). The three isolates I2: Bacillus cereus, AZS2: Bacillus subtilis and com- mercial strain AZB: Azospirillum brasilense) caused a highly significant increase in the total number of leaves ranging from 10.9% to 12.7% compared to the un-inoculated control. Seedlings inoculated with AZS2: Bacillus subtilis strain exhib- ited the highest aerial dry biomasses with an improvement of more than 85 % (30.76 g) compared with un-inoculated control plants and more than 62 % compared to un-inocu- lated NaCl control plants. The inoculation treatment with I2: Bacillus cereus strain induced an improvement of more than 65 % (27.44g) over un-inoculated control and more than 45 % over un-inoculated NaCl control. The strain AZS2: Bacillus subtilis produced the highest root dry weights, in compari- son to other isolates and induced an improvement of 30.17% (26.06 g) compared to un-inoculated plants (control) and 24.09% compared to un-inoculated plants (NaCl control). The most effective rhizobacterial treatment in the dry biomasses of whole seedling (aerial dry biomass and root dry biomass) is AZS2: Bacillus subtilis strain which induced an improvement of 55% (56.83 g) compared to un-inoculated plants (control) and 42% compared to un-inoculated plants (NaCl control). The most important production of kernels was recorded with AZS2: Bacillus subtilis strain. Consequently, this finding suggests that these PGPR strains could be useful for the development of inoculants biofertilizers to improve the quality and the health of the soil and the plant species by increasing the nutrient availability for the soil and plants especially in arid and semi-arid regions. Furthermore, using biofertilizers that contain these rhizobac- terial strains will led to a decrease in the use of chemical fer- tilizers and will provide high quality products free of harmful agrochemicals for human and environment. 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