Search

Salinity is one of the most serious agricultural problems that adversely affects growth and productivity of pasture crops such as alfalfa. In this study, the effects of salinity on some ecophysiological and biochemical criteria associated with salt tolerance were assessed in two Moroccan alfalfa (Medicago sativa L.) populations, Taf 1 and Tata. The experiment was conducted in a hydro-aeroponic system containing nutrient solutions, with the addition of NaCl at concentrations of 100 and 200 mM. The salt stress was applied for a month. Several traits in relation to salt tolerance, such as plant dry biomass, relative water content, leaf gas exchange, chlorophyll fluorescence, nutrient uptake, lipid peroxidation and antioxidant enzymes, were analyzed at the end of the experiment. The membrane potential was measured in root cortex cells of plants grown with or without NaCl treatment during a week. The results indicated that under salt stress, plant growth and all of the studied physiological and biochemical traits were significantly decreased, except for malondialdehyde and H2O2 contents, which were found to be increased under salt stress. Depolarization of membrane root cortex cells with the increase in external NaCl concentration was noted, irrespective of the growth conditions. The Tata population was more tolerant to high salinity (200 mM NaCl) and its tolerance was associated with the ability of plants to maintain adequate levels of the studied parameters and their ability to overcome oxidative stress by the induction of antioxidant enzymes, such as guaiacol peroxidase, catalase and superoxide dismutase.

Legumes, the second-most-important crop family, are a key source of biological nitrogen in agriculture and potentially contribute to sustainable cropping systems. Nevertheless, most legumes are salt sensitive, especially during biological nitrogen fixation (BNF). Therefore, improving legume growth and symbiosis efficiency under this constraint constitutes a great challenge to meet the increasing food demands and to protect soils from negative impacts of chemical fertilizers. In this perspective, silicon (Si) has been found to mitigate salt stress effect and improve legume development at the overall developmental stages. Whether direct or indirectly, Si counteracts salt stress effects on seed germination, plant growth and nodulation. The improvement of water uptake and nutrient homeostasis, the modification of gas exchange, the regulation of phytohormone and compatible solute biosynthesis and the regulation of the antioxidant metabolism under salinity are the key mechanisms evoked by plants upon Si treatment. Furthermore, during rhizobial symbiosis, Si has been shown to induce nodule formation and act on nodule functionality by increasing bacteroids and symbiosomes number, nitrogenase activity and leghemoglobin content under salinity. Here, we reviewed recent progress related to the role of exogenous Si in improving legume salt tolerance and highlighted the mechanisms through which Si could mediate salt tolerance. The needs of future research for better understanding how Si can promote salt tolerance in legumes are also addressed. [ABSTRACT FROM AUTHOR]

Moroccan soils, generally present low available phosphorus (P) levels which occur in almost all arid and semi-arid regions. Faba bean is one of the most significant crops in Morocco and is influenced by these constraints that affect its nutrient uptake and nitrogen fixation capacity and hence plants development. Therefore, we evaluated the response of four Vicia faba varieties - Aguadulce (Ag), Alfia (Al), Luz de Otono (LO) and Reina Mora (RM)-, grown under biological nitrogen fixation to water deficit and two phosphorus levels. The trial was conducted under greenhouse conditions and water stress was induced by keeping pots at 40% substrate field capacity (FC) versus 80% FC for the controls while phosphorus deficiency treatment consisted in the application of 25 µmol P plant-1 week-1 versus 125 µmol P plant-1 week-1 for sufficient P treatment. The results revealed a significant effect of water deficit and phosphorus deficiency either alone or combined on plants dry weights, leaf water parameters and nutrient concentrations. However sufficient phosphorus supply mitigated the adverse effects of water deficit on faba bean. We noticed significant differences between the studied varieties. Ag showed high performance concerning dry weights (1.25 g and 1.88 g plant-1 respectively for shoot and root) and high concentration of nitrogen N (4.7%) and P (0.27 mg g-1 DW) and was then qualified as the most tolerant variety to water deficit combined with P limitation. While RM was the least tolerant variety, as it showed the lowest dry weights (0.51 g and 1.4 g plant-1 respectively for shoot and root) and concentration (2.74% and 0.19 mg g-1 DW respectively for N and P). The tolerance was related to the ability to ensure efficient osmoregulation by glycine betaine accumulation, to keep leaf water balance and cell membrane stability that contribute together with adequate symbiotic nitrogen fixation to plant growth performance under combined stresses. [ABSTRACT FROM AUTHOR]

Legumes are plants able to engage in root nodule symbiosis with nitrogen-fixing soil bacteria, called rhizobia. This symbiotic interaction is highly specific, such that each rhizobial species interacts with only a specific group of legumes, and vice versa. The rhizobia and the host plant develop a dialogue system based on an exchange of chemical molecules. Many studies reported that the flavonoids, in combination with the rhizobial NodD transcriptional activator, stimulate the expression of the genes required in the perception and signal transduction of Nod factors and the genes of nodule formation. This review seeks to highlight the genes and molecular signals involved in legume-rhizobia symbiosis. Recent knowledge leading to bacterial access and nodule formation was focused and discussed. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Biological nitrogen fixation has positive effects in the enhancement of soil nutrition and plants growth, especially under difficult conditions. The study assesses the effect of drought (40% field capacity) on growth, physiological and biochemical parameters of six symbioses involving two Moroccan alfalfa populations Adis-Tata (Ad) and Riche (Rc) and Moapa (Mo) variety and ArfRh2 (Rh2) and AufRh8 (Rh8) rhizobia isolated from Arfoud and Aufous, respectively. Results showed that drought decreased plants growth and nodulation. Physiologically, as response to stress, the nodules membrane stability was negatively affected. Biochemically, activities of peroxidase (POX), catalase (CAT), superoxide dismutase (SOD) and acid phosphatase (APase) increased in leaves and nodules. Ad-Rh2, Rc-Rh2 and Ad-Rh8 have been qualified as more drought tolerant. They showed high antioxidant activities and as consequence less membrane damages especially in their nodules. The increase in nodules health and antioxidant defense could results in the enhancement of plant drought tolerance under stress. [ABSTRACT FROM AUTHOR]

The effects of water deficit on growth, nodulation, and several physiological and biochemical processes in six symbiotic combinations involving three Moroccan alfalfa (Medicago sativaL.) populations (Tafilalet1, Adis-Tata and Demnate2), an American Moapa variety and two rhizobial strains (RhL9 and RhL10) were studied. The experiment was conducted under greenhouse conditions. Seedlings were separately inoculated with the suspension of two rhizobial strains and grown under two irrigation regimes: 80% of field capacity (optimal irrigation) and 40% of field capacity (water deficit). The water stress was applied for five weeks and the agro-physiological and biochemical parameters related to water deficit tolerance were assessed. The results showed that the water deficit had significantly reduced the height of the plants, the dry biomass and nodulation. This constraint also negatively affected the relative water content of leaves, the membrane permeability, the stomatal conductance, the maximum quantum yield of photosystem II, the time to reach maximum fluorescence, the total chlorophyll content and the total nitrogen content. Comparison among the tested symbiotic combinations showed that their behaviors were significantly different. Under drought, oasis populations Ad and Ta maintained high PS II efficiency, membrane stability, relative water content, chlorophyll and nitrogen content in comparison to the mountain one Dm2 and the American Moapa variety. These parameters were maintained at adequate levels in the plants inoculated with the rhizobial strain RhL9 that showed a tolerance to water deficit conditions. [ABSTRACT FROM AUTHOR]

The present work was a study on the adverse effects of salinity on growth, nodulation, and some physiological parameters in 4 symbiotic combinations involving 2 Moroccan alfalfa (Medicago sativa L.) populations (Demnate and Tata) and 2 rhizobial strains (rhLAr 1 and rhLAr 4). The experiment was conducted in the greenhouse at 32/22 °C day/night, 50%-80% relative humidity, and a photoperiod of 16 h. The seedlings were separately inoculated with suspensions of 2 rhizobial strains and grown under 2 NaCl treatments, 0 mM (control) and 100 mM (salt stress), in plastic pots filled with sterile sand and peat at 9/10 and 1/10 ratios, respectively. The salt stress was applied for 5 weeks and some agro-physiological and biochemical parameters related to salt tolerance were assessed. The results showed that salinity significantly reduced the height of plants, their dry biomass, and nodulation. This constraint has also negatively affected the relative water content of leaves, the membrane permeability, the stomatal conductance, the maximum quantum yield of photosystem II, and the chlorophyll contents. Comparison among the symbiotic combinations tested showed that their behavior was significantly different. Plants inoculated with rhizobial strain rhLAr 4 were more tolerant to saline conditions. Their tolerance was associated with the maintaining of adequate levels in terms of physiological and biochemical parameters studied. [ABSTRACT FROM AUTHOR]

The present study aims to isolate endophytic actinomycetes (EPM) that are able to tolerate abiotic stresses, solubilize tricalcium phosphate (TCP) and produce indole-3-acetic acid (IAA), amylase and cellulose activities, while exhibiting high antagonistic activity against Fusarium oxysporum. f. sp. albedinis. Endophytic actinomycetes were isolated from roots, stems and leaves of Thymus saturoides and Lavandula multifida plant grown in Beni Mellal region, Morocco. According to the macro- and micro-morphological characteristics, a total of eleven EPM isolates were isolated and purified. Results indicated that the majority of isolates were able to tolerate pH and salt stresses. Moreover, the majority of the isolates were able to solubilize TCP on Pikovskaya (PVK)-agar medium which ranged from 25% to 458%. Additionally, on PVK-liquid medium, soluble phosphate content varied from 163.81 µg/mL recorded for the isolate LRP1 to 730 µg/mL observed for the isolate TSRP2. For IAA production, the amount produced varied from 1.70 µg/mL recorded for the isolate LRP1 to 14.13 µg/mL recorded for both LTP2' and TSRP2. Endophytic actinomycetes isolated in this work also showed a remarkable capacity to degrade some compounds such as cellulose and starch. In addition, some of them showed a strong inhibitory activity against the fungus F. albedinis with a percentage of inhibition ranged from 69.13% observed for LTP2' to 86.6% recorded for the isolate LRP2. Results from this study indicate that the two isolates LTP2' and TSRP2 were the most efficient and that actinomycetes could be used in biocontrol against the fungus F. albedinis. [ABSTRACT FROM AUTHOR]