Use of two bacteria for biological control of bayoud disease caused by Fusarium oxysporum in date palm (Phoenix dactylifera L) seedlings

Chemical Characterization and Antifungal Activity of Blue Tansy (Tanacetum annuum) Essential Oil and Crude Extracts against Fusarium oxysporum f. sp. albedinis, an Agent Causing Bayoud Disease of Date Palm

Tanacetum annuum L. is a Mediterranean plant, commonly known as Blue Tansy due to its blue colour as an essential oil, which is widely used for medicinal purposes. However, there are no studies on the bioactive compounds (especially, phenolic compounds) and the biological properties of their organic extracts. Herein, the purpose of the present work was to investigate the chemical composition of the essential oil and crude extracts of the T. annuum aerial parts collected from northern Morocco and to evaluate their antioxidant and antifungal activity against Fusarium oxysporum f. sp. albedinis, an agent causing Bayoud disease of the date palm, an important food source and commercial perennial crop in the Sahara and North Africa. Chemically, Folin-Ciocalteu and aluminium chloride colourimetric methods were used to determine the total phenolic (TPC) and total flavonoid (TFC) contents, respectively; polyphenols were characterized using HPLC-MS, while GC-MS was used to analyse the essential oil composition. Moreover, the evaluation of antioxidant and antifungal activities was carried out using the DPPH test and microdilution method, respectively. The results showed that the three T. annuum parts (stems, leaves and flowers) extracts contained important TPC and TFC with values varied between 51.32 and 116.32 mg/g of dry crude extract (DCE). HPLC-MS analysis revealed the identification and quantification of 19 phenolic acids and flavonoids with an emphasis on apigenin 7-glucoside (4540 µg/g of dry weight (DW)), luteolin 7-glucoside (2804 µg/g DW) and salicylic acid (1878 µg/g DW). Additionally, 39 biomolecules were identified in the essential oil using GC-MS, which were predominated by camphor (16.69%), α-pinene (12.37%), bornyl acetate (11.97%) and limonene (11.10%). The methanolic and hydro-methanolic extracts of T. annuum parts demonstrated a strong antioxidant property with IC50 values ranging between 0.22 and 0.65 mg/mL. Concerning antifungal activity, the essential oil and crude extracts of the Moroccan Blue Tansy exhibited a potent capacity against F. oxysporum f. sp. albedinis at low concentrations, with MIC and MFC values of 3.33 and 4.58 µL/mL for the essential oil and values of 3.33 and 9.17 mg/mL for crude extracts, respectively. Overall, these results demonstrated T. annuum as an important source of bioactive compounds and contribute significantly to the potential of using essential oils and extracts for controlling the Bayoud disease of date palms. Moreover, the finding suggests that T. annuum can be highly useful for phytosanitary and pharmaceutical industries.

Control Effect and Mechanism of Trichoderma asperellum TM11 against Blueberry Root Rot

Fusarium oxysporum is the primary pathogen of blueberry root rot; furthermore, we found that Fusarium commune can also cause root rot in blueberries. Trichoderma spp. is widely used to control plant diseases. We isolated Trichoderma asperellum (TM11) from blueberry rhizosphere soil to explore its control effect and mechanism on F. oxysporum and F. commune. We found that the inhibitory effects of TM11 volatiles and broth metabolites on F. oxysporum were significant, but only F. commune volatile metabolites had a significant inhibitory effect on its growth. Twelve known antimicrobial metabolites were detected from the methanol extract of TM11 fermentation broth by HPLC-MS. TM11 lysed and coiled around the hyphae of F. oxysporum and F. commune. The pot experiment showed that TM11 had significant control effects against F. oxysporum and F. commune, and inoculation of TM11 prior to that of F. oxysporum and F. commune was more effective. The TM11, TM11 and F. oxysporum, or F. commune and distilled water treatments had different effects on the activities of superoxide dismutase, peroxidase and catalase, and the enzyme activity levels exhibited the following order: TM11 > TM11 and F. oxysporum or F. commune > distilled water. The results showed that TM11 provided effective control of blueberry root rot.

Combination of Sodium Bicarbonate (SBC) with Bacterial Antagonists for the Control of Brown Rot Disease of Fruit

Simultaneous treatment with antagonistic bacteria Bacillus amylolquefaciens (SF14), Alcaligenes faecalis (ACBC1), and the food additive sodium bicarbonate (SBC) to control post-harvest brown rot disease caused by Monilinia fructigena, and their effect on the post-harvest quality of nectarines were evaluated. Four concentrations of SBC (0.5, 2, 3.5, and 5%) were tested. Results showed that bacterial antagonists displayed remarkable compatibility with different concentrations of SBC and that their viability was not affected. The results obtained in vitro and in vivo bioassays showed a strong inhibitory effect of all treatments. The combination of each bacterial antagonist with SBC revealed a significant improvement in their biocontrol efficacies. The inhibition rates of mycelial growth ranged from 60.97 to 100%. These results also indicated that bacterial antagonists (SF14 or ACBC1) used at 1 × 10⁸ CFU/ mL in combination with 2, 3.5, or 5% SBC significantly improved the control of M. fructigina by inhibiting the germination of spores. Interestingly, disease incidence and lesion diameter in fruits treated with SF14, ACBC1 alone, or in combination with SBC were significantly lower than those in the untreated fruits. In vivo results showed a significant reduction in disease severity ranging from 9.27 to 64.83% compared to the untreated control, while maintaining the appearance, firmness, total soluble solids (TSS), and titratable acidity (TA) of fruits. These results suggested that the improved disease control by the two antagonistic bacteria was more likely due to the additional inhibitory effects of SBC on the mycelial growth and spore germination of the pathogenic fungus. Overall, the combination of both bacteria with SBC provided better control of brown rot disease. Therefore, a mixture of different management strategies can effectively control brown rot decay on fruits.

Spatial-Temporal Water Balance Components Estimation Using Integrated GIS-Based Wetspass-M Model in Moulouya Basin, Morocco

The Moulouya basin in Morocco is one of many river basins around the world that are regulated with physical flow control, a range of regulations and storage structures. The water budget of the basin is unbalanced; the available water resources are insufficient for agricultural productivity, nature conservation and ecosystem services. This study evaluates spatial and temporal distributions of actual evapotranspiration, groundwater recharge and surface runoff for the period 2000–2020 using the WetSpass-M model in the Moulouya basin, Morocco. The WetSpass-M model’s input data are created in grid maps with the ArcGIS tool. They include monthly meteorological parameters (e.g., temperature, wind speed, rainfall,), soil map, land cover, topography, slope and groundwater depth. A good correlation has been observed between the simulated groundwater recharge and base flow, with the value of R2 = 0.98. The long-term spatial and temporal average annual precipitation of 298 mm is distributed as 45 mm (15.1%) groundwater recharge and 44 mm (14.8%) surface runoff, while 209 mm (70.1%) is lost through evapotranspiration. The simulated results showed that the average groundwater recharge of 15.1 mm (30%) falls during the summer and spring seasons, while the remaining 29.5 mm (70%) occurs during the winter and autumn seasons. Annually, 2430 million m3 of water recharges to the groundwater system from the rainfall for the entire basin. The study’s findings would help local stakeholders and policymakers in developing sustainable and effective management of available surface water and groundwater resources in the Moulouya basin.

Synthesis, characterization, reaction mechanism prediction and biological study of mono, bis and tetrakis pyrazole derivatives against Fusarium oxysporum f. sp. Albedinis with conceptual DFT and ligand-protein docking studies

Twelve heterocyclic compounds were prepared using the condensation of hydroxymethanol pyrazole derivatives with different primary aminesas example 2-aminothiazole and 1-aminobenzotriazole to have a diverse productin good yield up to 97%. Those ligands were tested against Fusarium oxysporum f. sp. Albedinis fungi (BAYOUD Disease) with IC₅₀ = 25.6-33.2 µg/ml. After experiments, theoretical investigations were done as DFT study to know the ligands molecular reactivity and the-ligandprotein- docking study to know the possible binding between the prepared ligands with two biological targets: FGB1 (Fusarium oxysporum Guanine nucleotide-binding protein beta subunitprimary amino acid sequence) and Fophy (Fusarium oxysporum phytase domain enzyme). Of all the obtained results, the experimental ones were well correlated with the theoretical with the most common thing between those compounds is (N^δ--N^δ+) which is the antifungal pharmacophore as proposed pincers for Foa inhibition. From docking studies over FGB1 and Fophy, the ligand 9 has the best binding energy of -6.4872 kcal/mol in FGB1 active site and -5.5282 kcal/mol in Fophy active site, but better correlation with Fophy than FGB1 which is followed by PLIF graph to get that Arg116, Arg120 and Lys336 are the vital amino acids of fophy protein based the study over the chosen active site.

Alcaligenes aquatilis GTE53: Phosphate solubilising and bioremediation bacterium isolated from new biotope "phosphate sludge enriched-compost"

The isolation and identification of beneficial bacteria from the active phase of composting is considered to be a key bio-quality parameter for the assessment of the process. The aim of this work was the selection and identification of beneficial bacteria from a co-composting experiment of vegetable waste (VW), olive oil mill waste (O₂MW), and phosphate sludge (PS). Phosphate-solubilizing strains were isolated from the thermophilic phase using Pikovskaya (PVK) solid medium supplemented with tricalcium phosphate Ca3(PO4) (TCP) as the sole source of phosphorus (P). Therefore, the selected isolate Alcaligenes aquatilis GTE53 was tested to tolerate abiotic stresses (different levels of temperature, variable pH, high salinity and water stress). The isolate was also assessed for indole acetic acid (IAA) and siderophores synthesis, nitrogen fixation, phenol degradation and pathogens inactivation. The quality of the co-composting process was also investigated by monitoring the physico-chemical parameters. The obtained results showed that A. aquatilis GTE53 displayed a higher solubilization index of 2.4 and was efficiently dissolved, up to 162.8 and 247.4 mg·mL^-1 of inorganic phosphate from PS and phosphate rock (PR), respectively. A. aquatilis GTE53 exhibited siderophores and IAA release, along with atmospheric nitrogen fixation. In addition to that, A. aquatilis GTE53 showed a high resistance to heat and tolerance to acidic and alkaline pH, high salinity and water stress. Moreover, A. aquatilis GTE53 could degrade 99.2% of phenol from a high-concentrated medium (1100 mg·L^-1 of phenol) and can inactivate the most abundant pathogens in industrial wastes: Escherichia coli, Streptococcus sp., Salmonella sp., and Fusarium oxysporum albedinis. Analysis of temperature, pH, electrical conductivity, carbon/nitrogen (C/N) ratio, indicated successful co-composting. An efficient transformation of P to the available form and a great abatement of polyphenols, were also recorded during the process. The findings of this study will help to advance the understanding of A. aquatilis GTE53 functions and will facilitate its application to promote beneficial microbial organisms during composting, thus obtaining a high-quality product.

Moroccan Groundwater Resources and Evolution with Global Climate Changes

In semi-arid areas, many ecosystems and activities depend essentially on water availability. In Morocco, the increase of water demands combined to climate change induced decrease of precipitation put a lot of pressure on groundwater. This paper reports the results of updating and evaluation of groundwater datasets with regards to climate scenarios and institutional choices. The continuous imbalance between groundwater extraction and recharge caused a dramatic decline in groundwater levels (20 to 65 m in the past 30 years). Additionally, Morocco suffers from the degradation in groundwater quality due to seawater intrusion, nitrate pollution and natural salinity changes. Climate data analysis and scenarios predict that temperatures will increase by 2 to 4 °C and precipitation will decrease by 53% in all catchments over this century. Consequently, surface water availability will drastically decrease, which will lead to more extensive use of groundwater. Without appropriate measures, this situation will jeopardize water security in Morocco. In this paper, we zoom on the case the Souss-Massa basin, where management plans (artificial recharge, seawater desalination, and wastewater reuse) have been adopted to restore groundwater imbalance or, at least, mitigate the recorded deficits. These plans may save water for future generations and sustain crop production.

Biocontrol activity and putative mechanism of Bacillus amyloliquefaciens (SF14 and SP10), Alcaligenes faecalis ACBC1, and Pantoea agglomerans ACBP1 against brown rot disease of fruit

This study aimed at evaluating the antagonistic activity of 16 bacterial strains for the control of brown rot disease caused by Monilinia fructigena, and M. laxa under in vitro and a semi-commercial large-scale trial. These bacterial antagonists' belonging to the genera Alcaligenes, Bacillus, Brevibacterium, Pantoea, Pseudomonas, and Serratia were previously proven effective for control of fire blight of apple. The in vitro dual culture bioassay showed the highest inhibition rates of mycelial growth ranging from 55 to 95% and from 43 to 94% for M. fructigena and M. laxa, respectively. The in vivo bioassay showed moderate and strong inhibition for M. fructigena and M. laxa, respectively. The inhibition rates were dependent on incubation time as well as pathogen virulence. The free-cell bacterial filtrate revealed substantial mycelial growth inhibition ranging from 66 to 86%. The inhibition of conidial germination was from 32 to 78%, suggesting the involvement of metabolites in their biocontrol activity. The antifungal effect of the volatile compounds (VCOs) was observed for all bacteria with mycelial inhibition varying from 12 to 70%. Overall, their efficacy was substantially affected by the nature of the bacterial strains and the modes of action. Taken together, these results underscore that ACBC1 and SF14 for M. fructigena and SP10 and ACBP1 for M. laxa were the most effective bacterial strains. These strains were confirmed effective in a semi-commercial large-scale trial. Interestingly, their efficacies were found to be comparable to those of both commercial BCAs (B. subtilis Y1336 and P. agglomerans P10c), but slightly lower than thiophanate-methyl fungicide. The ability of most bacterial strains to produce lytic enzymes (Amylase, Protease or Cellulase) and lipopeptides (bacillomycin, fengycin, iturin and surfactin) was demonstrated by biochemical and molecular analyzes. Therefore, our findings suggest that the bacterial antagonists ACBC1, SF14, SP10 and ACBP1, have the potential to prevent brown rot disease.

Bacillus subtilis: A plant-growth promoting rhizobacterium that also impacts biotic stress

Plants encounter many biotic agents, such as viruses, bacteria, nematodes, weeds, and arachnids. These entities induce biotic stress in their hosts by disrupting normal metabolism, and as a result, limit plant growth and/or are the cause of plant mortality. Some biotic agents, however, interact symbiotically or synergistically with their host plants. Some microbes can be beneficial to plants and perform the same role as chemical fertilizers and pesticides, acting as a biofertilizer and/or biopesticide. Plant growth promoting rhizobacteria (PGPR) can significantly enhance plant growth and represent a mutually helpful plant-microbe interaction. Bacillus species are a major type of rhizobacteria that can form spores that can survive in the soil for long period of time under harsh environmental conditions. Plant growth is enhanced by PGPR through the induction of systemic resistance, antibiosis, and competitive omission. Thus, the application of microbes can be used to induce systemic resistance in plants against biotic agents and enhance environmental stress tolerance. Bacillus subtilis exhibits both a direct and indirect biocontrol mechanism to suppress disease caused by pathogens. The direct mechanism includes the synthesis of many secondary metabolites, hormones, cell-wall-degrading enzymes, and antioxidants that assist the plant in its defense against pathogen attack. The indirect mechanism includes the stimulation of plant growth and the induction of acquired systemic resistance. Bacillus subtilis can also solubilize soil P, enhance nitrogen fixation, and produce siderophores that promote its growth and suppresses the growth of pathogens. Bacillus subtilis enhances stress tolerance in their plant hosts by inducing the expression of stress-response genes, phytohormones, and stress-related metabolites. The present review discusses the activity of B. subtilis in the rhizosphere, its role as a root colonizer, its biocontrol potential, the associated mechanisms of biocontrol and the ability of B. subtilis to increase crop productivity under conditions of biotic and abiotic stress.

Screening for Fusarium Antagonistic Bacteria From Contrasting Niches Designated the Endophyte Bacillus halotolerans as Plant Warden Against Fusarium

Date palm (Phoenix dactylifera L.) plantations in North Africa are nowadays threatened with the spread of the Bayoud disease caused by Fusarium oxysporum f. sp. albedinis, already responsible for destroying date production in other infected areas, mainly in Morocco. Biological control holds great promise for sustainable and environmental-friendly management of the disease. In this study, the additional benefits to agricultural ecosystems of using plant growth promoting rhizobacteria (PGPR) or endophytes are addressed. First, PGPR or endophytes can offer an interesting bio-fertilization, meaning that it can add another layer to the sustainability of the approach. Additionally, screening of contrasting niches can yield bacterial actors that could represent wardens against whole genera or groups of plant pathogenic agents thriving in semi-arid to arid ecosystems. Using this strategy, we recovered four bacterial isolates, designated BFOA1, BFOA2, BFOA3 and BFOA4, that proved very active against F. oxysporum f. sp. albedinis. BFOA1-BFOA4 proved also active against 16 Fusarium isolates belonging to four species: F. oxysporum (with strains phytopathogenic of Olea europaea and tomato), F. solani (with different strains attacking O. europaea and potato), F. acuminatum (pathogenic on O. europaea) and F. chlamydosporum (phytopathogenic of O. europaea). BFOA1-BFOA4 bacterial isolates exhibited strong activities against another four major phytopathogens: Botrytis cinerea, Alternaria alternata, Phytophthora infestans, and Rhizoctonia bataticola. Isolates BFOA1-BFOA4 had the ability to grow at temperatures up to 35°C, pH range of 5-10, and tolerate high concentrations of NaCl and up to 30% PEG. The isolates also showed relevant direct and indirect PGP features, including growth on nitrogen-free medium, phosphate solubilization and auxin biosynthesis, as well as resistance to metal and xenobiotic stress. Phylogenomic analysis of BFOA1-BFOA4 isolates indicated that they all belong to Bacillus halotolerans, which could therefore considered as a warden against Fusarium infection in plants. Comparative genomics allowed us to functionally describe the open pan genome of B. halotolerans and LC-HRMS and GCMS analyses, enabling the description of diverse secondary metabolites including pulegone, 2-undecanone, and germacrene D, with important antimicrobial and insecticidal properties. In conclusion, B. halotolerans could be used as an efficient bio-fertilizer and bio-control agent in semi-arid and arid ecosystems.

Secondary and sucrose metabolism regulated by different light quality combinations involved in melon tolerance to powdery mildew

We evaluated the effect of different light combinations on powdery mildew resistance and growth of melon seedlings. Light-emitting diodes were used as the light source and there were five light combinations: white light (420-680 nm); blue light (460 nm); red light (635 nm); RB31 (ratio of red and blue light, 3: 1); and RB71 (ratio of red and blue light, 7: 1). Compared with other treatments, blue light significantly decreased the incidence of powdery mildew in leaves of melon seedlings. Under blue light, H₂O₂ showed higher accumulation, and the content of phenolics, flavonoid and tannins, as well as expression of the genes involved in synthesis of these substances, significantly increased compared with other treatments before and after infection. Lignin content and expression of the genes related to its synthesis were also induced by blue light before infection. Melon irradiated with RB31 light showed the best growth parameters. Compared with white light, red light and RB71, RB31 showed higher accumulation of lignin and lower incidence of powdery mildew. We conclude that blue light increases melon resistance to powdery mildew, which is dependent on the induction of secondary metabolism that may be related to H₂O₂ accumulation before infection. Induction of tolerance of melon seeds to powdery mildew by RB31 is due to higher levels of sucrose metabolism and accumulation of lignin.

Bacillus: A Biological Tool for Crop Improvement through Bio-Molecular Changes in Adverse Environments

Crop productivity is affected by environmental and genetic factors. Microbes that are beneficial to plants are used to enhance the crop yield and are alternatives to chemical fertilizers and pesticides. Pseudomonas and Bacillus species are the predominant plant growth-promoting bacteria. The spore-forming ability of Bacillus is distinguished from that of Pseudomonas. Members of this genus also survive for a long time under unfavorable environmental conditions. Bacillus spp. secrete several metabolites that trigger plant growth and prevent pathogen infection. Limited studies have been conducted to understand the physiological changes that occur in crops in response to Bacillus spp. to provide protection against adverse environmental conditions. This review describes the current understanding of Bacillus-induced physiological changes in plants as an adaptation to abiotic and biotic stresses. During water scarcity, salinity and heavy metal accumulate in soil, Bacillus spp. produce exopolysaccharides and siderophores, which prevent the movement of toxic ions and adjust the ionic balance and water transport in plant tissues while controlling the pathogenic microbial population. In addition, the synthesis of indole-3-acetic acid, gibberellic acid and1-aminocyclopropane-1-carboxylate (ACC) deaminase by Bacillus regulates the intracellular phytohormone metabolism and increases plant stress tolerance. Cell-wall-degrading substances, such as chitosanase, protease, cellulase, glucanase, lipopeptides and hydrogen cyanide from Bacillus spp. damage the pathogenic bacteria, fungi, nematodes, viruses and pests to control their populations in plants and agricultural lands. The normal plant metabolism is affected by unfavorable environmental stimuli, which suppress crop growth and yield. Abiotic and biotic stress factors that have detrimental effects on crops are mitigated by Bacillus-induced physiological changes, including the regulation of water transport, nutrient up-take and the activation of the antioxidant and defense systems. Bacillus association stimulates plant immunity against stresses by altering stress-responsive genes, proteins, phytohormones and related metabolites. This review describes the beneficial effect of Bacillus spp. on crop plants, which improves plant productivity under unfavorable climatic conditions, and the current understanding of the mitigation mechanism of Bacillus spp. in stress-tolerant and/or stress-resistant plants.

Bacillus amyloliquefaciens strain 32a as a source of lipopeptides for biocontrol of Agrobacterium tumefaciens strains

AIMS

A Bacillus amyloliquefaciens strain, designated 32a, was used to identify new compounds active against Agrobacterium tumefaciens and to evaluate their efficiency to control crown gall on carrot discs.

METHODS AND RESULTS

Based on PCR-assays, four gene clusters were shown to direct the synthesis of the cyclic lipopeptides surfactin, iturin A, bacillomycin D and fengycin. Mass spectrometry analysis of culture supernatant led to the identification of these secondary metabolites, except bacillomycin, with heterogeneous mixture of homologues. Antimicrobial assays using lipopeptides-enriched extract showed a strong inhibitory activity against several bacterial and fungal strains, including Ag. tumefaciens. Biological control assays on carrot discs using both 32a spores and extract resulted in significant protection against crown gall disease, similar to that provided by the reference antagonistic strain Agrobacterium rhizogenes K1026.

CONCLUSIONS

In contrast to all active compounds against Ag. tumefaciens that are of proteinaceous nature, this work enables for the first time to correlate the strong protective effect of B. amyloliquefaciens strain 32a towards crown gall disease with the production of a mixture of lipopeptides.

SIGNIFICANCE AND IMPACT OF THE STUDY

The findings could be useful for growers and nursery men who are particularly interested in the biocontrol of the crown gall disease.

Antagonistic action of Bacillus subtilis strain SG6 on Fusarium graminearum

Fusarium graminearum causes Fusarium head blight (FHB), a devastating disease that leads to extensive yield and quality loss of wheat and barley. Bacteria isolated from wheat kernels and plant anthers were screened for antagonistic activity against F. graminearum. Based on its in vitro effectiveness, strain SG6 was selected for characterization and identified as Bacillus subtilis. B. subtilis SG6 exhibited a high antifungal effect on the mycelium growth, sporulation and DON production of F. graminearum with the inhibition rate of 87.9%, 95.6% and 100%, respectively. In order to gain insight into biological control effect in situ, we applied B. subtilis SG6 at anthesis through the soft dough stage of kernel development in field test. It was revealed that B. subtilis SG6 significantly reduced disease incidence (DI), FHB index and DON (P ≤ 0.05). Further, ultrastructural examination shows that B. subtilis SG6 strain induced stripping of F. graminearum hyphal surface by destroying the cellular structure. When hypha cell wall was damaged, the organelles and cytoplasm inside cell would exude, leading to cell death. The antifungal activity of SG6 could be associated with the coproduction of chitinase, fengycins and surfactins.