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This research aimed to study diversity among a collection of Rhizoctonia solani strains, isolated from many crops in Morocco, based on radial mycelial growth on potato dextrose agar (PDA) at different pH and temperature levels. The in vitro antifungal efficacy of essential oils (EOs) derived from aromatic and medicinal plants of Thymus vulgaris, Origanum compactum, Rosmarinus officinalis, Eucalyptus sp., Salvia sp., Cistus ladanifer and Lavandula stoechas was also evaluated by measuring the mycelial growth of this plant pathogenic fungus after placing active mycelial plugs of each strain on Petri dishes using a disc diffusion method of EOs. The Minimum Inhibitory Concentration (MIC) of each EO was also determined. The growth rates observed under different temperatures and pH levels varied among isolates and did not show similar responses for the same levels of the two growth parameters. However, the maximum mycelial growth of the majority of isolates was reached between 20 and 30°C as well as at pH 7. Among the EOs tested, the results revealed that EO of Thymus vulgaris and Origanum compactum were very effective on controlling R. solani strain RS1 with growth inhibition rate of 75,9% and 60,6%, respectively. The MIC of these EOs was at 0.03%. According to the gas chromatography analysis, Carvacrol (61.8%) and thymol (47.8%) are the major constituents of O. compactum and T. vulgaris EOs, respectively, suggesting that these natural compounds have important potential to control R. solani and could be useful for developing effective organic fungicides.

Olive knot disease caused by Pseudomonas savastanoi pv. savastanoi (PSS) is considered as the main bacterial disease of olive tree in Morocco. However, sole prophylactic measures are available. The main aim of this work was to evaluate the effects of eighteen antagonistic bacteria, as an alternative approach, to control in vitro and in planta the pathogens strains previously isolated from olive trees in Morocco. In vitro experiments revealed that many bacterial strains such as Rahnella aquatilis, Enterobacter ludwiqii, Paenibacillus brasiliensis, and Bacillus subtilis selected from collection of Regional Center of Agronomic Research, were efficient on solid media against pathogen strains. Their inhibition zones ranged from 8 to 23 mm with a higher inhibition rates found by B. subtilis strains. Enzymatic activities of antagonistic strains were assessed (cellulase, protease and amylase) as well as some plant growth promotion traits (phosphorus solubilisation and indole acetic acid production) for performance screening. B. subtilis 2515-1 was selected for pots experiment using olive trees (cv. Arbequina). This bacterium significantly reduced number and weight of knots against two pathogens strains (PSS 2064-8 and PSS 2102-4). The most reduction rates of weight and knot number were respectively 95.60% and 50%. This study suggested an alternative approach to assess the efficiency of selected bacterium in field conditions.

In order to discover new natural resources with biological properties, the chemical composition, the antioxidant and antimicrobial activities, and the potential use as food preservative of essential oils of Moroccan Achillea odorata subsp. pectinata (AOpEO) and Ruta montana (RMEO) were studied. Gas chromatography-mass spectrometry (GC-MS) analysis revealed the presence of 21 and 25 compounds in AOpEO and RMEO, respectively. The results showed that the major compounds of AOpEO are camphor (45.01%), bornyl acetate (15.07%), borneol (11.33%), &beta, eudesmol (4.74%), camphene (3.58%), and 1.8-cineole (eucalyptol) (2.96%), whereas 2-undecanone (63.97%), camphor (3.82%) and cyclopropanecarboxylic acid (3.66%) were the main components of RMEO. The antioxidant activities were evaluated by diphenylpicrylhydraziyl radical (DPPH) and reducing power assays. The antimicrobial activities of essential oils were tested against bacterial strains and food contaminant yeast using agar disc diffusion and microdilution methods. A significant antimicrobial activity of AOpEO was observed against Bacillus subtilis, Proteus mirabilis and Candida albicans, compared to RMEO. The efficacy of AOpEO was also evaluated in model food systems (cabbage and barley) artificially inoculated during storage. The results found that the adding of a minimal inhibitory concentration (MIC) and 4&times, MIC were potent in decreasing the Proteus mirabilis growth in food model systems. Our findings suggested that AOpEO may be potentially used as an alternative food preservative.

Early Access: DEC 2019; International audience; AIMS: Crown gall, a phytobacteriosis characterized by the formation of tumours on plant roots was observed in recently planted vineyards of the Meknes region (Morocco). The objective of this research was to analyze the diversity of pathogenic agrobacteria isolated from grapevine in Morocco. METHODS AND RESULTS: Eighty-two isolates from 11 affected vineyards were characterized by recA sequencing and were found to belong to A. tumefaciens genomospecies G1, G4 or G7, Rhizobium rhizogenes, and to Allorhizobium vitis. Only the A. vitis isolates appeared to be pathogenic on tomato and MLSA phylogenetic analyses revealed a weak genetic diversity, with the definition of only four genomic groups. Definition of the A. vitis genomic groups correlateds with specific pathogenic traits: indeed, genomic groups differed with respect to the severity of hypersensitive response symptoms on tobacco leaves, the intensity of necrotic response on grapevine explants, and opine profiles. Both vitopine and octopine were detected by UHPLC in tumors induced by isolates of three genomic groups, an opine signature scarcely ever reported. CONCLUSIONS: Allorhizobium vitis is the only causative agent of crown gall on grape in Morocco, pathogenic isolates can be separated into four genomic groups. SIGNIFICANCE AND IMPACT OF THE STUDY: This study of recently crown-gall-infested vineyards demonstrated that Allorhizobium vitis is the only causative agent and revealed the presence of non-pathogenic Agrobacterium strain within tumors. Moreover, as the genetic diversity of the A. vitis isolates is relatively narrow, this study lays the basis for further analyses on the evolution of the disease, on the dissemination of the pTi and more globally on the fate of the different genomic groups in this newly colonized environment.

A rapid method and sensitive methods for extraction of bacterial DNA from pure culture and directly from plant materiel were compared in polymerase chain reaction with specific primers VCF3/VCR3 to see the reliable method that can used in the detection of tumorigenic strain of Allorhizobium vitis causal agent of grapevine crown gall. From the three tested methods of DNA extraction from pure culture, the alkaline method is the most effective technique for the extraction presenting a high sensitivity with a detection threshold equal to 5.104 CFU/ml. Five different protocols for extracting bacterial DNA from plant tissues of infected tomato, based on the use of an extraction buffer, were tested to see its usefulness in detecting pathogenic strain of A. vitisS4. Two protocols based on the use of Triton X-100 and Tween 20 were efficient for detecting A. vitis S4 directly from tomato tumors with a sensitivity of 103 CFU/ml for the both protocols. Consequently, these protocols were proposed as specific protocols for the detection of tumorigenic strain of A. vitis from symptomatic and asymptomatic plants.

This study aims to determine the phytochemical compounds of Cistus ladaniferus subsp. ladanifer and Mentha suaveolens and the investigations of their antibacterial effects against phytopathogenic bacteria. The chemical composition of Cistus ladaniferus subsp. ladanifer essential oils (CLEO) and Mentha suaveolens essential oils (MSEO) was determined using GC-MS analysis. The determination of phenolic content (TPC) of ethanolic, methanolic, and water plant extracts was realized by the Folin-Ciocalteu method. In vitro antibacterial activity was tested against Pseudomonas savastanoi pv. savastanoi 2636-40 and Clavibacter michiganensis subsp. michiganensis 1616-3 using agar disc diffusion and microdilution assay. Efficacy of the extracts in the treatment of the tomato infected seeds by Clavibacter michiganensis in Petri plate assays. The chemical composition of MSEO revealed the presence of piperitenone oxide (39.11%), and germacrene D (13.6%) as a main compound. However, viridiflorol (28.82%) and Ɣ-gurjunene (14.61%) were the main compounds of CLEO. Among the extracts of Mentha suaveolens, the methanolic extract is the richest in phenol content (112.04 ± 2.98 mg EAG/g of extract), while the aqueous extract is richer on phenol content (76.98 ± 4.6 mg EAG/g of extract) for Cistus ladaniferus. The antibacterial activity showed important inhibition of plant pathogenic bacteria. The Petri plate assays indicated that 4×MIC of methanolic extract of C. ladaniferus showed the highest percentages of tomato germination seeds inoculated by C. michiganensis with rates of 77.77%. These findings suggest that methanolic extract of Cistus ladaniferus may be used as ecofriendly management of plant pathogens bacteria. However, further investigations concerning the identification of phenolic compounds of these plant extracts and the evaluation of antibacterial mechanism against plant pathogens bacteria are required.

International audience; Allorhizobium (Agrobacterium) vitis is a host-specific pathogenic bacterium that causes grapevine crown gall disease, affecting vine growth and production worldwide. The antibacterial activities of different aromatic plant essential oils were tested in vitro and in planta against A. vitis. Among the essential oils tested, those of Origanum compactum and Thymus vulgaris showed the most significant in vitro antibacterial activities, with a MIC of 0.156 and 0.312 mg/mL, respectively. A synergistic effect of these two essential oils (1:1) was observed and confirmed by the checkerboard test. Carvacrol (61.8%) and thymol (47.8%) are, respectively, the major compounds in the essential oils of O. compactum and T. vulgaris and they have been shown to be largely responsible for the antibacterial activities of their corresponding essential oils. Results obtained in vitro were reinforced by an in planta pathogenicity test. A mixture of O. compactum and T. vulgaris essential oils (1:1), inoculated into the injured stem of a tomato plant and a grapevine at 0.312 mg/mL as a preventive treatment, reduced both the number of plants developing gall symptoms and the size of the tumors.