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The vascular wilt of date palm (Phoenix dactylifera L.), also known as Bayoud and caused by Fusarium oxysporum f.sp. albedinis (FOA), is the most destructive disease in North Africa. The disease has resulted in huge economic losses due to declining crop yield and quality. The use of potential biocontrol agents is a sustainable and environmentally friendly strategy compared to synthetic fungicides. The use of date palm-associated microflora for the screening of native antagonistic bacteria with potential applications is the most promising way to control this disease. Thus, the epidemic palm groves (in the valley of M'zab-Ghardaia-Algeria) were chosen for the isolation of rhizospheric bacteria and endophytes from the soil and roots of healthy or infected plants. A total of 8 bacterial isolates (83, 84, 300, 333, 322, 260, 249, and 227) selected from 75 FOA-active strains, showed strong activity against several strains of FOA and other major plant pathogens. Their phylogenetic identification proved they belong to the genus Bacillus (Bacillus sp., B. subtilis, B. atrophaeus, B. halotolerans, B. amyloliquefasiens, and B. paralicheformis). Bacterial cultures and a cell-free culture supernatant tested alone or in co-culture showed FOA inhibitory activity. However, the effect of the co-culture did not show any synergy in both cases. Unlike diffusible compounds, volatile organic compounds did not show a significant antifungal ability. The concept of selecting biocontrol agents in vitro does not always guarantee in vivo performance. In addition to antibiosis, other strategies such as competition and resistance induction are required for biocontrol agent efficacy. To evaluate the biocontrol effect in vivo, germinated seeds of date palm were treated with bacteria, infected with the pathogen, and then incubated for 45 days at room temperature in the dark. The majority of the strains (84, 300, and 333) tested showed moderate fungistatic effects and the protection rate reached an average of 60%. In particular, promising results were obtained with B. paralicheniformis strain 260 which significantly protected palm seeds up to 85%, compared to its in vitro test where a low inhibition rate (27.77%) was recorded. Screening methods should be equipped with multifactorial or plant-mediated control mechanisms. Furthermore, these bacteria have shown other potentialities to improve plant growth and resist stressful conditions. Thus, an effective biocontrol agent must combine several beneficial characteristics to be used successfully in situ. In this respect, Bacillus remains the best candidate for biological control. [ABSTRACT FROM AUTHOR]

Biotic and abiotic stresses are severely limiting plant production and productivity. Of notable importance is salt stress that not only limits plant growth and survival, but affects the soil fertility and threatens agricultural ecosystems sustainability. The problem is exacerbated in fragile arid and semi-arid areas where high evaporation, low precipitation and the use of salty water for irrigation is accelerating soil salinization. Legumes, considered very nutritious foods for people and providing essential nutrients for ecosystems are a fundamental element of sustainable agriculture. They can restore soil health by their ability to fix nitrogen in a symbiotic interaction with the rhizobia of the soil. However, salt stress is severely limiting productivity and nitrogen fixation ability in legumes. Plant growth-promoting rhizobacteria (PGPR) and mainly actinobacteria promote plant growth by producing phytohormones, siderophores, antibiotics and antifungal compounds, solubilizing phosphate and providing antagonism to phytopathogenic microorganisms. In addition, actinobacteria have beneficial effects on nodulation and growth of legumes. In this study, actinobacteria isolated from different niches and having PGP activities were used in co-inoculation experiments with rhizobia in Medicago sativa plants rhizosphere submitted to salt stress. The results indicate that drought- and salinity-tolerant Actinobacteria with multiple PGP traits can potentially increase alfalfa growth under saline conditions, in the presence or absence of symbiotic rhizobial bacteria. Actinobacteria discovered in this study can, therefore, be suitable biofertilizers in the formulation of agricultural products improving plant development, health and productivity in saline soils, a necessary alternative for modern agriculture and sustainable development. [ABSTRACT FROM AUTHOR]

Halophyte Limoniastrum monopetalum, an evergreen shrub inhabiting the Mediterranean region, has well-documented phytoremediation potential for metal removal from polluted sites. It is also considered to be a medicinal halophyte with potent activity against plant pathogens. Therefore, L. monopetalum may be a suitable candidate for isolating endophytic microbiota members that provide plant growth promotion (PGP) and resistance to abiotic stresses. Selected for biocontrol abilities, these endophytes may represent multifaceted and versatile biocontrol agents, combining pathogen biocontrol in addition to PGP and plant protection against abiotic stresses. In this study 117 root culturable bacterial endophytes, including Gram-positive (Bacillus and Brevibacillus), Gram-negative (Proteus, Providencia, Serratia, Pantoea, Klebsiella, Enterobacter and Pectobacterium) and actinomycete Nocardiopsis genera have been recovered from L. monopetalum. The collection exhibited high levels of biocontrol abilities against bacterial (Agrobacterium tumefaciens MAT2 and Pectobacterium carotovorum MAT3) and fungal (Alternaria alternata XSZJY-1, Rhizoctonia bataticola MAT1 and Fusarium oxysporum f. sp. radicis lycopersici FORL) pathogens. Several bacteria also showed PGP capacity and resistance to antibiotics and metals. A highly promising candidate Bacillus licheniformis LMRE 36 with high PGP, biocontrol, metal and antibiotic, resistance was subsequently tested in planta (potato and olive trees) for biocontrol of a collection of 14 highly damaging Fusarium species. LMRE 36 proved very effective against the collection in both species and against an emerging Fusarium sp. threatening olive trees culture in nurseries. These findings provide a demonstration of our pyramiding strategy. Our strategy was effective in combining desirable traits in biocontrol agents towards broad-spectrum resistance against pathogens and protection of crops from abiotic stresses. Stacking multiple desirable traits into a single biocontrol agent is achieved by first, careful selection of a host for endophytic microbiota recovery; second, stringent in vitro selection of candidates from the collection; and third, application of the selected biocontrol agents in planta experiments. That pyramiding strategy could be successfully used to mitigate effects of diverse biotic and abiotic stresses on plant growth and productivity. It is anticipated that the strategy will provide a new generation of biocontrol agents by targeting the microbiota of plants in hostile environments. [ABSTRACT FROM AUTHOR]