الفهرس 
1. IntroductionOnly 14 pages are availabe for public view
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Abstract
A greenhouse experiment was carried out as a pot experiment during summer season of 2016 in the Experimental Greenhouse of Department of Soil science, Faculty of Agriculture, Shbin El Kom, Menoufia University, to investigate and evaluate the efficiency of both liquid and solid inoculum of Bradyrhizobium spp (N2-fixing bacteria) alone or with plant growth promoting rhizobacteria (PGPR); Azotobacter chroococcum DSM 2286, as co-inoculation to inhibit the negative impact of salinity of irrigation wateron peanut plants grown in cultivated sandy soils.This soilwas collected from the surface layer (0- 30 cm) of the cultivated regions of Sadat city Menoufia Governorate, Egypt.As well as to comparatively evaluate the responses and identify the most suitable cultivar either Giza 6 or Gregoryto the studied treatments. Peanut seeds were inoculated with solid or liquid inoculum of Bradyrhizobium alone or with Azotobacter chroococcum DSM 2286 (PGPR) as co-inoculation, and planted in a sandy soils. Azotobacter chroococcum DSM 2286 originally isolated from the salt affected soil in Wadi El Natroon, Behiera Governorate, Egypt, it‘s having higher survival capabilities at different salinity levels, relatively higher potentials of nitrogenase activity, and P solubilization capacity, and IAA production.These strain was previously defined by genotypic identification which performed by amplification and partial nucleotide sequencing of the 16s rihbosomal DNA (16s rDNA) (El Zemrany et al., 2015). At 75 days after sowing, nodulation, dehydrogenase activity of rhizospheric soil of two peanut cultivars, fresh and dry weights of the growing plants and their elemental composition, mainly contents of nitrogen, phosphorus, potassium, iron, zinc and manganese were determined, seed, straw and pods weight (gm/plant), as well as quality traits of the seed of % proteinand oil%, were determined after harvest (130 days) of the two peanut cultivars. Saline irrigation water was collected from: i- BahreShibine El Kom,
as a source of Nile Water (563 mg L-1) (W1), ii- Groundwater artesian well,about 1000 mg L-1 (W2) and iii- Groundwater artesian wellabout 2000 mg L-1 (W3), were collected from cultivated regions of Sadat city. The standard recommended cultivation practices had been performed in the present study.
The biofertilizers inoculation treatments as follows:
1- Control treatments (without any biofertilizers inoculation).
2- Inoculation by solid Bradyrhizobium alone.
3- Inoculation by liquid Bradyrhizobium alone.
4- Co-inoculation: by solid Bradyrhizobium + PGPR (Azotobacter chrococoum).
5- Co-inoculation: by liquid Bradyrhizobium fertilization + PGPR (Azotobacter chrococoum).
The obtained results could be summarized as follows:
I- Fresh and dry matter yield
1.1. Inoculation treatments produced a high value of fresh (FMY) and dry (DMY) roots and stems, g/plant at 75 days after sowing of both Giza 6 and Gregory peanut cultivars compared to uninoculated treatments, under three salinity levels of irrigation water.
1.2. Co-inoculation treatments i.e. Azotobacter chrococoum with both solid and liquid Bradyrhizobium gave the highest values of fresh and dry roots and stems (g/plant) of both Giza 6 and Gregory peanut cultivars compared to the inoculation treatments of Bradyrhizobium alone at all experimental variables.
1.3. The maximum obtained values of DMY shoots of Giza 6 cultivar peanut plant were; 12.46, 10.90 and 9.64 gplant-1, while, thier were; 13.39, 11.41 and 10.52 gplant-1, for Gregory cultivar inoculated by Liquid
Bradyrhizobium +A. chroococcum, irrigated with the three salinity levels, W1, W2 and W3, respectively.
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1.4. Relative changes (RC %) of root and shoots FMY and DMY of both Giza 6 and Gregory peanut cultivars, a result of all inoculation treatments showed a positive indicator in comparison with an uninculated one. The highest RC of root and shoots FMY and DMY were observed withGregory cultivar plants inoculated by liquid Brady + A. chroococcumunder W3salinity level of irrigation water. These results concluded that, the inoculation treatments with Bradyrhizobium + PGPR (Co- inoculation, A. chroococcum) were able to mitigate the adverse effects of salinity stress of irrigation water up to 2000 mgl- 1on the peanut plants.
2. Microbiological parameter
2.1. Number of nodules and its dry weight:
2.1.1. Number of nodules and their dry weight were significantly increased by inoculation of Bradyrhizobiumspp alone or with Azotobacter chroococcum of the two peanut cultivars, compared touninoculated treatments.
2.1.2. Regarding to, Co-inoculation treatment of liquid Bradyrhizobium spp + Azotobacter chroococcum of Giza 6 cultivar peanut plants at 75 days after sowing appeared a high values of both number of nodules of Giza 9 cultivar (192, 169 and 135 nodule/plant) and their dry weight (406, 329 and 288 mgplant-1), and with Gregory cultivar 201, 175 and 141 nodule/plant (nodule number), and 431, 372 and 332 mg plant-1 (nodule dry weight) atthe same above mentioned salinity levels of irrigation water, respectively.
2.1.3. Co-inoculation treatments by liquid Bradyrhizobium spp+ Azotobacter chroococcum displayed a high RC values with the two peanut cultivars, than those occurred with the other experimental treatments. The presence of PGPR (co-inoculation) `
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in the rhizosphere enhanced legume nodulation and nitrogen fixation by affecting signal exchange between the plants and Bradyrhizobia.
2.1.4. The bacterial nodules number formed on the roots of the Gregory cultivar plants were higher than that formed on the roots of the Giza6 cultivar under the liquid Bradyrhizobium spp + Azotobacter chroococcum treatment. This findings means that, Gregory cultivar of peanut plants are more available confirmation to bacterial growth and nodules formation when compared with the Giza 6 cultivar plants.
2.2. Dehydrogenase activity ”DHA” in soil
Dehydrogenase activity (DHA) is frequently used as a measurement of the overall microbial activity in soil.
2.2.1. Dehydrogenase activity (μg formazan g-1soil hour-1) in the rhizospheric soil of the inoculated peanut plants exceeded that one of the uninoculated plants. Determination of the enzyme activity exhibited a variation among the different inoculation treatments of both cultivar peanut plants.
2.2.2. The co-inoculation treatments with Azotobacter chroococcum DSM 2286 with solid or liquid Bradyrhizobium spp. induced a higher increasesin the ”DHA” than those with the treatments of solid or liquid Bradyrhizobium spp alone. Inoculation treatments showed a most positive effect on the determined parameters of both cultivar plants, particularly with the first level of irrigation water.
2.2.3. The rhizospheric soil of Gregory peanut cultivar plants attained higher values of RC rates (%) of the dehydrogenase activity in comperison with the Giza 6 peanut cultivar plants, with the assigned experimental treatments.
3. Chemical constituents
3.1. Seed oil content
3.1.1. In general, responses of Gregory cultivar peanut plants to inoculation treatments significantly surpassed that one of Giza 6 cultivar peanut plants, under all tested treatments.
3.1.2. The seed oil content (%) of Giza 6 cultivar peanut plants, affected with the highest salinity level of irrigation water (2000 mg L-1) ranged from 47.20 to 48.57%, for Gregory cultivar peanut plants inoculated by liquid Bradyrhizobium spp + Azotobacter chroococcum, respectively.
3.1.3. Relative changes ”RC, %” of seed oil content in the plants inoculated by liquid Bradyrhizobium spp + Azotobacter chroococcum, under the same salinity levels of irrigation water were: 3.19, 2.63 and 2.1%, of Giza 6 cultivar peanut plants, and were 5.67, 3.10 and 3.37 of Gregory cultivar peanut plants, with inoculation treatment, respectively.
3.2. Seed protein content.
3.2.1. Liquid Bradyrhizobium sp + Azotobacter chroococcum presented the highest seed protein content than the other inoculation treatments under all treatments of study, where protein content were 24.81, 22.76 to 21.28 % for Giza 6 cultivar peanut plantsand were 26.47, 25.59 to 24.05 % for Gregory cultivar with the three saline levels of irrigation water, respectively.
3.2.2. At all inoculation treatments seed protein content (%)of Gregory cultivar peanutexceeded that one of Giza 6 cultivar.
3.2.3. Inoculation with liquid Bradyrhizobium and Azotobacter chroococcum, attained increases in RC %of seed protein content (%), where these values were 34.23, 27.67 and 23.53%, for the Giza 6 cultivar peanut
plants and were 39.37, 36.09 and 31.97%, for the Gregory cultivar under the three salinity levels of irrigation water, respectively.
3.3. Macro and micronutrient contents in shoots and seeds of peanut plants.
3.3.1. There were enhancement in N, P, K, Fe, Zn and Mncontent in both shoots and seeds of two cultivars of peanut plants due to the inoculation with solid or liquid Bradyrhizobium spp aloneor with Azotobacter chroococcum DSM 2286, as Co-inoculationunder all studiedtreatments of irrigation water.
3.3.2. Co-inoculation with Azotobacter chrococoum, augmented nitrogen, phosphorus and potassium contents in shoots and seedsmore than application of solid or liquid Bradyrhizobium spp alone.The inoculation treatments of Azotobacter chrococoum + liquid Bradyrhizobium obviously promotedmacro (N, P and K) and micronutrient (Fe, Zn and Mn) concentrations and its uptake of both cultivars peanut plants, irrigated with the three salinity levels of water.
3.3.3. Likewise, inoculation treatments by Azotobacter chroococcum, as Co-inoculation remarkably stimulated Fe, Zn and Mn concentrations and its uptake in the shoots and seeds of Giza 6 and Gregory peanut plants, with the three salinity levels of irrigation water.
3.3.4. Generally all bacterial inoculum markedly enhanced Fe, Zn and Mn concentration and its uptake of shoots and seeds of Gregory peanut plants cultivar inoculated compared to Giza 6 cultivar with the application of the experimental treatments.
4. Yield and yield attributes:
4.1. Number and weight of pods per plant
4.1.1. Number and weight of pods of Giza 6 and Gregory cultivars peanut plants, increased with all inoculation treatments under the three salinity levels of irrigation water.
4.1.2. Inoculation treatment by Azotobacter chroococcum with liquid Bradyrhizobium augmented number of pods/plant up to 41.31, 34.95 and 28.94 of Giza and 6 42.54, 38.31 and 32.24, of Gregory cultivar peanut plants with the three salinity levels of irrigation water, respectively.
4.1.3. Gregory cultivar showed the highest values of number and weight of pod per plant compared to Giza6 cultivar, received all treatments study.
4.2. Number and weight of seed per plant
4.2.1. The inoculation of Azotobacter chroococcum, as Co-inoculation with liquid Bradyrhizobium raised number of seeds/plant up to 55.62, 47.64 and 40.40 of Giza 6 and 60.13, 54.72 and 47.07 of Gregory cultivarsirrigated with Nile water, 1000 mgl-1and 2000 mgL-1 salinity levels of irrigation water, respectively.
4.2.2. The highest values of ”RC, %” seeds weight were obtained with inoculation by Azotobacter chroococcum added to liquid Bradyrhizobium spp that were 80.00, 72.69 and 67.29% of Giza 6 and 101. 07, 95.55 and 82.86% of Gregory peanut cultivars plants irrigated with the same sources of saline water, respectively.
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4.3. Weight of straw per plant
4.3.1. Co-inoculation treatments with Azotobacter chroococcum, considerably enhanced the weight straw (g/plant) of Giza 6 and Gregory cultivar peanut plants compared to inoculation treatments by solid or liquid Bradyrhizobium spp alone irrigated with the three salinity levels of water.
4.3.2. Gregory cultivar revealeda highvalues of weight straw (g/plant) compared to Giza 6 cultivar under all treatment studied.
4.3.3. Liquid Bradyrhizobium + Azotobacter chroococcum produced the highest values of ”RC, %” of weight straw (g/plant) compared to the other inoculation treatments.
All studied parameters responded to the inoculation with solid or liquid Bradyrhizobium spp alone or with Azotobacter chroococcum DSM 2286, as Co-inoculation according to following orders, referring to each salinity levels of irrigation water:
- For inoculation treatments:
Liquid Bradyrhizobium spp + Azotobacter chroococcum > solid Bradyrhizobium spp + Azotobacter chroococcum > liquid Bradyrhizobium spp alone > solid Bradyrhizobium spp alone.
- For peanut cultivars:
Gregory cultivar > Giza 6 cultivar.
It could be concluded that inoculation by liquid Bradyrhizobium + Azotobacter chroococcumseems to be the recommended treatment for producing optimum seed and straw yield and other parameters studied.Likewise it achieved the least production costs, also reducing the harmful effects of salinity of soil and/or irrigation water. It is also well established that, drip irrigation system gave ability to adding liquid Bradyrhizobium, several times during period of nodule formation. This period represents the crucial stage at which the plants would be under considerable stress owing to high nodulation which required conceivable amount of energy. The presences of Azotobacter chroococcum help the plants to overcome this initial stress, subsequently leading to vigorous establishment of plants. It is also important to mention that the Azotobacter chroococcum DSM 2286, as co-inoculation, may help the plants to save its requirements from nitrogen in the beginning of the plant life until the nodule become effective through nitrogen fixation. These in turn reflect an increase in dry matter yield and after that pod, seed and straw yield.
Results of this study imply that combined application of Bradyrhizobium and Azotobacter chroococcum DSM 2286, as co-inoculation,is becoming an efficient strategy for enhancing the productivity of peanut plants, as well as to provide legume plants with natural bioprotection against harmful effects of salinity of irrigation water of two cultivar peanut plants, practically, with the expected increases in salinization artesian wells water in newly reclaimed soils in Egypt. However, this approach could be explored as an effective strategywith least production costs to improve salt tolerance index in peanut plants underdrip irrigation systemin newly reclaimed soils in Egypt.