The inoculation of crops with growth-promoting bacteria is an interesting alternative to be considered to reduce the intensive use of chemical fertilizers in agriculture. This experiment is being conducted to test the effect of Plant Growth Promoting Bacteria (PGPB) on the growth and yield of oats and durum wheat grown with minimal nitrogen inputs. Three Rhizobium spp. strains, namely (L1, L2 and L3) isolated from root nodules trapped with Lupinus albus L. were used to assess the germination and growth of these crops. In a second step, these strains were tested on durum wheat grown under different nitrogen fertilization treatments (without nitrogen fertilization, applying 50 and 100

The search for ecofriendly products to reduce crop dependence on synthetic chemical fertilizers presents a new challenge. The present study aims to isolate and select efficient native PGPB that can reduce reliance on synthetic NPK fertilizers. A total of 41 bacteria were isolated from the sediment and roots of mangrove trees (Avicennia marina) and assessed for their PGP traits under in vitro conditions. Of them, only two compatible strains of Bacillus species were selected to be used individually and in a mix to promote tomato seedling growth. The efficiency of three inoculants applied to the soil was assessed in a pot experiment at varying rates of synthetic NPK fertilization (0, 50, and 100% NPK). The experiment was set up in a completely randomized design with three replications. Results showed that the different inoculants significantly increased almost all the studied parameters. However, their effectiveness is strongly linked to the applied rate of synthetic fertilization. Applying bacterial inoculant with only 50% NPK significantly increased the plant height (44-51%), digital biomass (60-86%), leaf area (77-87%), greenness average (29-36%), normalized difference vegetation index (29%), shoot dry weight (82-92%) and root dry weight (160-205%) compared to control plants. Concerning the photosynthetic activity, this treatment showed a positive impact on the concentrations of chlorophyll a (25-31%), chlorophyll b (34-39%), and carotenoid (45-49%). Interestingly, these increases ensured the highest values significantly similar to or higher than those of control plants given 100% NPK. Furthermore, the highest accumulation of N, P, K, Cu, Fe, Zn, and Ca in tomato shoots was recorded in plants inoculated with the bacterial mix at 50% NPK. It was proven for the first time that the native PGP bacteria derived from mangrove plant species A. marina positively affects the quality of tomato seedlings while reducing 50% NPK.

IntroductionIn the Near East and North Africa (NENA) region, crop production is being affected by various abiotic factors, including freshwater scarcity, climate, and soil salinity. As a result, farmers in this region are in search of salt-tolerant crops that can thrive in these harsh environments, using poor-quality groundwater. The main staple food crop for most of the countries in this region, Tunisia included, is barley.MethodsThe present study was designed to investigate the sensitivity and tolerance of six distinct barley genotypes to aridity and salinity stresses in five different natural field environments by measuring their photosynthetic activity.Results and discussionThe results revealed that tolerant genotypes were significantly less affected by these stress factors than sensitive genotypes. The genotypes that were more susceptible to salinity and aridity stress exhibited a significant decline in their photosynthetic activity. Additionally, the fluorescence yields in growth phases J, I, and P declined significantly in the order of humid environment (BEJ), semi-arid site (KAI), and arid environment (MED) and became more significant when salt stress was added through the use of saline water for irrigation. The stress adversely affected the quantum yield of primary photochemistry (φP0), the quantum yield of electron transport (φE0), and the efficiency by trapped excitation (ψ0) in the vulnerable barley genotypes. Moreover, the performance index (PI) of the photosystem II (PSII) was found to be the most distinguishing parameter among the genotypes tested. The PI of sensitive genotypes was adversely affected by aridity and salinity. The PI of ICARDA20 and Konouz decreased by approximately 18% and 33%, respectively, when irrigated with non-saline water. The reduction was even greater, reaching 39%, for both genotypes when irrigated with saline water. However, tolerant genotypes Souihli and Batini 100/1B were less impacted by these stress factors.The fluorescence study provided insights into the photosynthetic apparatus of barley genotypes under stress. It enabled reliable salinity tolerance screening. Furthermore, the study confirmed that the chlorophyll a fluorescence induction curve had an inflection point (step K) even before the onset of visible signs of stress, indicating physiological disturbances, making chlorophyll fluorescence an effective tool for identifying salinity tolerance in barley.

Today, using plant growth–promoting rhizobacteria is an important eco-friendly management approach for improving crop productivity. This study aimed to select efficient native rhizobia from white lupin nodules and assess their potential for improving the production and economic returns of Triticum turgidum spp . durum L. var. Razzek under field conditions in arid and semi-arid environments affected by salinity and drought stress. Seventy-two strains were assessed for their plant growth-promoting activities. Of them, three compatible strains of Agrobacterium spp. were selected and used individually and in mixes. The efficiency of seven inocula applied to the soil was assessed in a pot experiment at varying levels of synthetic nitrogen fertilization (0, 50, and 100%N). The experiment was set up in a completely randomized design with four replications. At the flowering stage plant height, flag leaf area, shoot dry weight, leaf chlorophyll content, chlorophyll fluorescence, and the normalized difference vegetation index were estimated. Subsequently, the most efficient inoculant was tested in a field trial under four different agro-environmental conditions contrasting in terms of salt and drought stress, respecting the same N fertilization rates and experimental design, with three replications. Yield components, nitrogen (N) and phosphorus (P) contents, and economic returns were estimated at harvest time. In the pot experiment, a combined application of the mix of three Agrobacterium spp. at 50%N proved to be the best treatment ensuring the highest values for all the measured parameters, which were statistically similar or higher than those recorded in uninoculated plants receiving 100%N. Field inoculation trials confirmed the results obtained in the pot experiment. In non-stressed environments, application of the bacterial mix at 50%N was as effective as the 100%N treatment. Meanwhile, under drought and salt stress conditions, the same treatment significantly increased grain yield by 33 to 42% and straw yield by 13 to 22% compared to uninoculated plants at 100%N. Furthermore, this treatment significantly enhanced N and P contents in wheat straw and grain in stressed environments. An economic analysis revealed that application of the selected mix with 50%N increased net-returns per hectare, ensuring a financial gain ranging from 26 to 106% compared to the control plants receiving a full N dose. The positive effect of the native Agrobacterium sp. mix on growth, yield, nutrition, and economic returns of durum wheat var. Razzek, when combined with 50%N, was proved for the first time. However, future studies should now focus on examining the behavior of this mix with other durum wheat varieties.

The existing issues of climate change and population development have driven to a rising realization of the need to innovate in sustainable agricultural practice, such as intercropping, in parallel, improving the effectiveness of intercropping systems by applying beneficial micro-organisms (rhizobacteria and/or mycorrhizae) is a valuable approach. In this regard, two experiments were conducted to assess the effect of inoculation with beneficial microorganisms: rhizobacteria (B), mycorrhizae, and (M) rhizobacteria-mycorrhizae consortium (B+M) compared to the control (uninoculated plants: C) on Vetch/Oat/Triticale intercropping system. Growth, physiologicals traits, forage yield and qualities were determined at two harvesting periods (74 and 142 days after seeding: DAS). Overall, the different studied intercrops varied in term of inoculations effect. Mycorrhizal inoculation had a significantly positive effect on SPAD, total nitrogen and leaf to stem ratio for vetch, Oat and Triticale, respectively. Bacteria inoculation promoted leaf area and plant height for Vetch and Oat crops and only plant height for Triticale. The dual bacteria and mycorrhizae inoculum improved significantly the yield dry matter (YDM) by 41.2% ensuring an increase of 2.1 and 1.67 tons/ha at 74 and 142 DAS respectively, compared to control treatment. Further data analysis revealed an improvement of calcium and phosphorus status after mycorrhizae inoculation. This study highlighted the potential applications of the dual biofertilizers on Vetch/Oat/Triticale intercropping as way to increase forage yield and qualities in semi-arid region.

The purpose of this investigation was to assess the nodulation and the plant growth of white lupin (Lupinus albus L.) in Tunisian soils. For this, two L. albus varieties, Mekna (Tunisian) and Lumen (French), were cultivated in soils sampled from 56 locations without a history of lupin cultivation or rhizobial inoculation. All soils were analyzed for their physical and chemical proprieties. At harvest, nodulation and plant growth parameters were recorded for both varieties. The results showed that 75% of soils were alkaline and calcareous. Nodulation was often poor, suggesting the absence of host-specific rhizobia. It was absent in 41 soils, abundant in 2 (Sejnen and Mraissa), and scarce but efficient in the remaining 13 soils. Furthermore, white lupin varieties have different responses to native nodulating bacteria since the local variety, Mekna, developed significantly more root nodules and in more soils than the imported variety. Growth parameters and nitrogen accumulation were also measured as indicators of nitrogen fixation efficiency. Considerable variability was detected among soils. It was found that the imported variety, Lumen, showed high sensitivity to the soil active lime content compared to Mekna. Interestingly, high biomass production and nitrogen accumulation were recorded in soils originating from Madian, Tejerouin, Benouria, and Oued zinga, with a high active lime content ranging from 26% to 31%. This finding suggested that white lupin can be cultivated in Tunisian calcareous soils, especially the most promising local variety, Mekna. Isolation and the selection of efficient bacteria from alkaline calcareous soils are necessary to promote the development of this valuable legume in Tunisia.

In order to expand the cultivation of white lupin and improve its nodulation and growth in Tunisian soils, twenty native strains affiliated to the Rhizobium and Agrobacterium genera were used in this study. Phenotypic characterization identified a strain, LAb8, that was highly tolerant of different types of abiotic stress under in vitro conditions, including pH variation (4-11), drought (15-30% PEG600) and salinity (600-1500 mM NaCl). With cultivation in sterilized carrier sand, the nodulation test highlighted the efficiency of this strain in increasing shoot dry weight (+208%) and nitrogen accumulation (+116%) compared to unfertilized control plants. Subsequently, a pot experiment was conducted to elucidate the potential of these selected strains applied as liquid and solid inoculants to promote nodulation and growth, as well as the nitrogen content of white lupin plants grown in non-sterilized soils. The results showed that inoculation with LAb8 significantly increased nodulation in terms of number (+95-118%) and dry weight (213-296%), whether as a solid or liquid inoculant. Significant increases were recorded in inoculated plants for leaf chlorophyll content (+9-11%), plant height (+16-18%), shoot and root dry weight (+38-44% and +51-61% respectively) compared to unfertilized control plants. Interestingly, compared to unfertilized control plants, application of the selected strain induced higher shoot nitrogen accumulation varying from 71% to 79% for liquid and solid inoculants, respectively. Furthermore, the solid inoculant was more efficient than its equivalent, the liquid inoculants gave the best dry nodular biomass and nitrogen content, respectively + (26%) and (+ 5%) respectively than the liquid form.

With a view to introducing white lupin (Lupinus albus L.) for cultivation in Tunisian calcareous soils, compatible indigenous rhizobia for nitrogen-fixing symbiosis were investigated and characterized. Two L. albus varieties, Mekna and Lumen, were used to trap rhizobia in soil samples collected from 56 sites with high active lime contents (0–49%). Nodulation occurred in only 15 soils. The local variety, Mekna, developed significantly more root nodules and had a trapping capacity in more soils than the imported variety Lumen. A phylogenetic analysis based on the partial 16S-23S ribosomal RNA internal transcribed spacer region (ITS) and multi-locus sequence analysis (MLSA) of three chromosomal housekeeping genes, recA, atpD and dnaK, showed that strains were affiliated to Agrobacterium, Rhizobium, and Neorhizobium, with large internal diversity, including separate lineages. Infectivity tests highlighted some nodulation specificity at the plant variety level, since the strains originating from Mekna could only nodulate this variety, while strains trapped in Lumen could nodulate both varieties. When inoculated, almost all strains resulted in a significant increase in plant shoot dry weight on L. albus. Although Agrobacterium sp. strains isolated from L. albus could nodulate and had a plant growth promoting effect, no nodA and nodC genes could be amplified. This is discussed together with the absence of bradyrhizobia and the general infrequency of L. albus–nodulating rhizobia in Tunisian soils. The adapted and efficient rhizobial strains reported here were promising candidates for inoculant development and represent a contribution towards successful cultivation of L. albus in Tunisia, especially the most promising Mekna variety.

Hedysarum coronarium L. cultivated on calcareous soil in Northern Tunisia was the subject of a trial attempted under field condition, to figure out the effect of nitrogen fertilizer and Rhizobium inoculation on their growth, nodulation and mineral content. Rhizobium inoculation enhanced significantly all growth parameters compared to the nitrogen fertilization especially at the flowering stage. No significance difference was shown between the uninoculated check and the nitrogen fertilized plants concerning the nodule number per plant at all plant stage. At 154 DAS (Day After Sowing) and 174 DAS, Rhizobium inoculated plants set a high mean nodule number (86.33 and 77.77 respectively). Nodule weight per plant was high in Rhizobium inoculated plants compared to the uninoculated check and the nitrogen fertilized plants especially at 123 DAS, 154 DAS and 174 DAS. Concerning nutrients content in shoot of sulla at flowering stage, Nitrogen fertilization significantly enhanced nutrients content. However rhizobial inoculation has almost doubled nutrients uptake compared to the nitrogen fertilized control.