Abstract:& Key message Selection of the best salt-tolerant combination of Casuarina sp. and arbuscular mycorrhizal fungi (AMF) is one of the key criteria for successful setup of saline land rehabilitation program. & Context Land salinization is a serious problem worldwide that mainly leads to soil degradation and reduces crop productivity. These degraded areas could be rehabilitated by planting salt-tolerant species like Casuarina glauca Sieb. and Casuarina equisetifolia L. These are pioneer plants, able to form symbio… Show more
“…The higher frequencies and intensities in co-inoculated P.agg + Rf plants would explain the salt tolerance of this strain. The work of Djighaly et al (2018) showed significant metabolic activity of R. fasciculatus at 300 mM NaCl. But also to the additional effect of PGPR which improves the phosphate nutrition of the plant (Egamberdieva et al, 2019).…”
Section: Discussionmentioning
confidence: 92%
“…This effect was related to an increase in K+ content accompanied by an effective decrease in Na+ in plant tissues. The positive effect co-inoculation P. agg + Rf on growth parameters could be explained by the fact that P. agglomerans, is a halophilic, nitrogen-fixing and phosphate-solubilizing strain, capable of producing of indole acetic acid (AIA) up to 600 mM NaCl (Hasfa, 2014) and AMF (R. fasciculatus) in improving salt tolerance stress among Casuarina species (Djighaly et al, 2018). In the presence of salt, these microorganisms participate in the selective absorption of ions such as phosphorus, nitrogen and magnesium and in the reduction of Na+ ion absorption (Giri and Mukerji, 2004;Chen et al, 2014;Paul and Sinha, 2017).…”
Section: Discussionmentioning
confidence: 99%
“…After 3 weeks of acclimatization, the control plants were watered with 0 mM and the stressed plants with 150 and 300 mM of NaCl. The choice of these concentrations was made on the basis of previous studies on Casuarina by Djighaly et al (2018).…”
Salinity is one of the main abiotic stresses limiting plant growth and development. However, the use of salt-tolerant plants combined with beneficial soil microorganisms could improve the effectiveness of biological methods for saline soil recovery. The aim of this study is to identify the Casuarina obesa/ Arbuscular Mycorrhizal fungi (AMF)/Plant Growth Promoting Rhizobacteria (PGPR) association that could be used in salt-land rehabilitation programs. Thus, the plants were grown under greenhouse on sandy soil, inoculated either with PGPR (Pantoea agglomerans and Bacillus sp.), or with AMF (Rhizophagus fasciculatus and Rhizophagus aggregatum) or co inoculated with PGPR and AMF and watered with a saline solution (0, 150, and 300 mM). After 4 months of cultivation, the plants were harvested and the results obtained showed that inoculation improves the survival rate, height and biomass of the plants compared to the control plants. The results also showed that inoculation increases the total amount of chlorophyll and the accumulation of plant proline at all levels of salt concentration. However, P. agglomerans and Bacillus sp. strains alone or in combination with R. fasciculatus increased plant growth. This study showed that these strains of PGPR, whether or not associated with AMF, could be biological tools to improve C. obesa performance under saline stress conditions.
“…The higher frequencies and intensities in co-inoculated P.agg + Rf plants would explain the salt tolerance of this strain. The work of Djighaly et al (2018) showed significant metabolic activity of R. fasciculatus at 300 mM NaCl. But also to the additional effect of PGPR which improves the phosphate nutrition of the plant (Egamberdieva et al, 2019).…”
Section: Discussionmentioning
confidence: 92%
“…This effect was related to an increase in K+ content accompanied by an effective decrease in Na+ in plant tissues. The positive effect co-inoculation P. agg + Rf on growth parameters could be explained by the fact that P. agglomerans, is a halophilic, nitrogen-fixing and phosphate-solubilizing strain, capable of producing of indole acetic acid (AIA) up to 600 mM NaCl (Hasfa, 2014) and AMF (R. fasciculatus) in improving salt tolerance stress among Casuarina species (Djighaly et al, 2018). In the presence of salt, these microorganisms participate in the selective absorption of ions such as phosphorus, nitrogen and magnesium and in the reduction of Na+ ion absorption (Giri and Mukerji, 2004;Chen et al, 2014;Paul and Sinha, 2017).…”
Section: Discussionmentioning
confidence: 99%
“…After 3 weeks of acclimatization, the control plants were watered with 0 mM and the stressed plants with 150 and 300 mM of NaCl. The choice of these concentrations was made on the basis of previous studies on Casuarina by Djighaly et al (2018).…”
Salinity is one of the main abiotic stresses limiting plant growth and development. However, the use of salt-tolerant plants combined with beneficial soil microorganisms could improve the effectiveness of biological methods for saline soil recovery. The aim of this study is to identify the Casuarina obesa/ Arbuscular Mycorrhizal fungi (AMF)/Plant Growth Promoting Rhizobacteria (PGPR) association that could be used in salt-land rehabilitation programs. Thus, the plants were grown under greenhouse on sandy soil, inoculated either with PGPR (Pantoea agglomerans and Bacillus sp.), or with AMF (Rhizophagus fasciculatus and Rhizophagus aggregatum) or co inoculated with PGPR and AMF and watered with a saline solution (0, 150, and 300 mM). After 4 months of cultivation, the plants were harvested and the results obtained showed that inoculation improves the survival rate, height and biomass of the plants compared to the control plants. The results also showed that inoculation increases the total amount of chlorophyll and the accumulation of plant proline at all levels of salt concentration. However, P. agglomerans and Bacillus sp. strains alone or in combination with R. fasciculatus increased plant growth. This study showed that these strains of PGPR, whether or not associated with AMF, could be biological tools to improve C. obesa performance under saline stress conditions.
“…Meanwhile, 15 PCD-related genes were induced by SA or JA to participate in the salt stress response. Interestingly, selection of appropriate fungal strains is crucial for improving C. equisetifolia performance in saline soils ( Djighaly et al, 2018 ). The effect of Frankia symbiosis on salt tolerance of C. equisetifolia will be our next research focus.…”
Background
High soil salinity seriously affects plant growth and development. Excessive salt ions mainly cause damage by inducing osmotic stress, ion toxicity, and oxidation stress. Casuarina equisetifolia is a highly salt-tolerant plant, commonly grown as wind belts in coastal areas with sandy soils. However, little is known about its physiology and the molecular mechanism of its response to salt stress.
Results
Eight-week-old C. equisetifolia seedlings grown from rooted cuttings were exposed to salt stress for varying durations (0, 1, 6, 24, and 168 h under 200 mM NaCl) and their ion contents, cellular structure, and transcriptomes were analyzed. Potassium concentration decreased slowly between 1 h and 24 h after initiation of salt treatment, while the content of potassium was significantly lower after 168 h of salt treatment. Root epidermal cells were shed and a more compact layer of cells formed as the treatment duration increased. Salt stress led to deformation of cells and damage to mitochondria in the epidermis and endodermis, whereas stele cells suffered less damage. Transcriptome analysis identified 10,378 differentially expressed genes (DEGs), with more genes showing differential expression after 24 h and 168 h of exposure than after shorter durations of exposure to salinity. Signal transduction and ion transport genes such as HKT and CHX were enriched among DEGs in the early stages (1 h or 6 h) of salt stress, while expression of genes involved in programmed cell death was significantly upregulated at 168 h, corresponding to changes in ion contents and cell structure of roots. Oxidative stress and detoxification genes were also expressed differentially and were enriched among DEGs at different stages.
Conclusions
These results not only elucidate the mechanism and the molecular pathway governing salt tolerance, but also serve as a basis for identifying gene function related to salt stress in C. equisetifolia.
“…Their contribution to the improvement of the growth of several plant species under saline conditions is well known [107,108] (Table 4). This is mainly related to a combination of biochemical, physiological, and nutritional effects [97,[109][110][111][112][113][114][115][116]. Among the mechanisms involved in salinity tolerance in AMF inoculated plants, we have the enhancement of water absorption capacity and nutrient uptake, the accumulation of osmoregulators like proline and sugars [105], the ionic homeostasis [87,117], and the reduction in Na + and Cl − uptake [118].…”
Section: Less Oxidative Damage Promoted Plant Growth and Enhancedmentioning
Arbuscular mycorrhizal fungi (AMF) establish symbiotic associations with most terrestrial plants. These soil microorganisms enhance the plant’s nutrient uptake by extending the root absorbing area. In return, the symbiont receives plant carbohydrates for the completion of its life cycle. AMF also helps plants to cope with biotic and abiotic stresses such as salinity, drought, extreme temperature, heavy metal, diseases, and pathogens. For abiotic stresses, the mechanisms of adaptation of AMF to these stresses are generally linked to increased hydromineral nutrition, ion selectivity, gene regulation, production of osmolytes, and the synthesis of phytohormones and antioxidants. Regarding the biotic stresses, AMF are involved in pathogen resistance including competition for colonization sites and improvement of the plant’s defense system. Furthermore, AMF have a positive impact on ecosystems. They improve the quality of soil aggregation, drive the structure of plant and bacteria communities, and enhance ecosystem stability. Thus, a plant colonized by AMF will use more of these adaptation mechanisms compared to a plant without mycorrhizae. In this review, we present the contribution of AMF on plant growth and performance in stressed environments.
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