Effect of fungicides and Trichoderma harzianum on sclerotia of Sclerotium rolfsii

The effect of three fungicides (benomyl, hymexazol, oxyquinoleine) on the viability of sclerotia of Sclerotium rolfsii was tested in natural and sterilized soils. A similar test was carried out in natural soil combining each of these fungicides with one of four isolates of Trichoderma harzianum. In addition, the mycelial growth of the T. harzianum isolates and S. rolfsii was monitored on agar media amended with these fungicides at three concentrations. Benomyl reduced the antagonistic ability of the T. harzianum isolates in the soil, oxyquinoleine yielded variable results, while hymexazol improved the antagonism of T. harzianum isolates. In an agar medium, benomyl inhibited all T. harzianum isolates, as did oxyquinoleine. By contrast, hymexazol had only a negligible effect on the growth of the antagonist

Induced Systemic Resistance (ISR) in Arabidopsis thaliana by Bacillus amyloliquefaciens and Trichoderma harzianum Used as Seed Treatments

International audienceThe Trichoderma fungal species and the bacteria Bacillus species were described as inducers of plant systemic resistance in relation to their antagonistic activity. The objective of this study was to evaluate the effect of selected strains of Bacillus amyloliquefaciens (I3) and Trichoderma harzianum (A) on inducing systemic resistance in Arabidopsis thaliana as a model for plant molecular genetics. The microorganisms were identified and were confirmed for their antagonistic potential in vitro and in vivo in previous studies. In order to explore this mechanism, two mutants of A. thaliana carrying a PR1 promoter (a conventional marker of salicylic acid (SA) pathway) and LOX2 promoter (a marker triggering jasmonic acid (JA) pathway activation) were analyzed after inoculating antagonists. Transgenic reporter line analysis demonstrated that B. amyloliquefaciens I3 and T. harzianum A induce A. thaliana defense pathways by activating SA and JA at a high level compared to lines treated with chemical elicitors of references (acibenzolar-S-methyl (Bion 50 WG (water-dispersible granule)), SA, and methyl jasmonate). The efficacy of B. amyloliquefaciens I3 and T. harzianum A in inducing the defense mechanism in A. thaliana was demonstrated in this study

Antifungal activity of bioactive compounds produced by the endophyte Bacillus velezensis NC318 against the soil borne pathogen Sclerotium rolfsii Sacc

In a previous study, the endophytic Bacillus velezensis NC318 was isolated from the rhizosphere of date palm and showed strong antifungal activity against the soil-borne plant pathogenic fungus, Sclerotium rolfsii Sacc, the causal agent of Southern blight. The potential of the Bacillus genus in the inhibition of plant pathogens is mainly due to the production of certain bioactive compounds. In the present study, secondary metabolites extracted from the cell-free supernatant of strain NC318 showed strong antifungal activity on the mycelial growth and germination of S. rolfsii sclerotia in vitro. With 50 μl of bioactive compounds crude extracts, the mycelial growth inhibition rate was 97% and any germination of sclerotia was reported. Chemical analysis of the secondary metabolite crude extracts performed by high performance liquid chromatography coupled with mass spectrometry (HPLC/MS), revealed that the secreted bioactive compounds belonged to the family of lipopeptides (iturin, fengycin, surfactin), polyketides (bacillaene, macrolactin, difficidin and bacilysin) and siderophores (bacillibactin). These results provide a better understanding of the biocontrol mechanism of the bacteria strain B. velezensis NC318 against the soil fungal pathogens, especially S. rolfsii root rot

Effect of nitrogen fertilizers and Trichoderma harzianum on Sclerotium rolfsii

The effect of urea, sulfate ammonium, nitrate potassium and horse manure on S. rolfsii was tested in vitro, alone and in combination with T. harzianum. Tests on liquid culture media showed that Sclerotium rolfsii did not utilize urea as a source of nitrogen while sulfate ammonium and nitrate potassium allowed the growth of the fungus. On a solid medium, the fertilizers at rates of 12 g N·m–2 and 18 g N·m–2 had an inhibitory effect on the growth of Sclerotium rolfsii mycelium. The highest effect was observed for urea. In contrast, Trichoderma harzianum assimilated all fertilizers but had a preference for sulfate ammonium. The antagonistic activity of Trichoderma harzianum on Sclerotium rolfsii on solid culture media was stimulated in the presence of the three nitrogen sources. The horse manure at high rates inhibited the growth of S. rolfsii, favored the development of T. harzianum and enhanced its antagonistic effect on S. rolfsii. The confrontation of Trichoderma harzianum with sclerotia of Sclerotium rolfsii in soil fertilized separately with urea, sulfate ammonium, nitrate potassium or manure showed an increase in the antagonistic activity. Particularly, the manure in combination with T. harzianum induced high mortality of sclerotia of the fungus. In the agronomic context of the region of Doukkala, it seems adequate to add these nitrogen sources to contribute to the biological control of Sclerotium rolfsii

Efficacy of Secondary Metabolites Produced by Bacillus Amyloliquefaciens on the Inhibition of Zymoseptoria Tritici

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Efficacy of a Bacillus velezensis strain in the biocontrol of sugar beet root rot caused by Sclerotium rolfsii Sacc

Dans une précédente étude, Bacillus velezensis NC318, une souche bactérienne antagoniste isolée de la rhizosphère du sol d’une culture de palmier dattier dans la région du Tafilalet, a montré un haut potentiel antagoniste in vitro contre la pourriture racinaire de betterave sucrière causée par Sclerotium rolfsii Sacc. Le présent travail consistait à évaluer in vivo l’incidence et la sévérité de la maladie sur plants de betteraves sucrières en pot sous serre. 147 jours après le semis dans un sol infesté par les sclérotes de ce pathogène (40 sclérotes /250 g de sol), les résultats ont montré que la bactérie appliquée par la bactérisation des semences ou dans le sol naturellement infesté a pu inhiber totalement la germination des sclérotes et par la suite aucune infection des plantes de betteraves sucrières n’a été observée. Aussi une amélioration des paramètres de croissance des plants (le poids frais de la partie aérienne des plants, le poids frais des racines, la longueur des pousses et le nombre de feuilles) des plantes issues de semences traitées avec la souche NC318 a été enregistrée. Le test de la viabilité de la souche antagoniste NC318 sur les semences bactérisées et stockées à 4 °C, a montré que cet antagoniste est resté viable après cinq mois de conservation et a préservé son potentiel antagoniste contre S. rolfsii testé in vitro. Ces résultats suggèrent que la souche NC318 pourrait potentiellement être un agent de biocontrôle pour lutter contre S. rolfsii avec un effet biostimulateur de la croissance des plantes.In a previous study, Bacillus velezensis NC318, an antagonistic bacterial strain isolated from the rhizosphere of the soil of a date palm crop in the Tafilalet region, showed a high in vitro antagonistic potential against sugar beet root rot caused by Sclerotium rolfsii Sacc. The present work consisted in evaluating in vivo the incidence and severity of the disease on sugar beet plants in pots under a greenhouse. 147 days after sowing in a soil infested with sclerotia of this pathogen (40 sclerotia /250 g of soil), the results showed that the bacterium applied by bacterization of the seeds or in the naturally infested soil was able to totally inhibit the germination of the sclerotia and subsequently no infection of sugar beet plants was observed. Moreover, an improvement of plant growth parameters (fresh weight of the aerial part of the plants, fresh weight of the roots, length of the shoots and, the number of leaves) of plants from seeds treated with strain NC318 was recorded. Viability testing of the antagonist strain NC318 on treated seeds stored at 4 °C, showed that this antagonist remained viable after five months of storage and preserved its antagonistic potential against S. rolfsii tested in vitro. These results suggest that strain NC318 could potentially be a biocontrol agent to control S. rolfsii with a biostimulator effect on plant growth. &nbsp

Occurrence of Sclerotium rolfsii Inducing Sugar Beet Root Rot and its Sustainable Management by Acting on Soil Fertility in Western Morocco

In Morocco, and particularly in the Doukkala irrigated perimeter, sugar beet rot caused by Sclerotium rolfsii is a major limiting factor for the productivity of this crop. The objective of this study was to identify the relationship between the frequency of Sclerotium rolfsii infestation and the quantity of viable sclerotia in the soil on the one hand, and with the different physicochemical parameters of the soil in cropped sugar beet fields on the other hand. In total, 1794 soil samples were collected during a four years period in the whole irrigated perimeter. These samples were analyzed for their sclerotial content. In addition, laboratory analysis of physico-chemical parameters was performed for 94 sugar beet fields in 2019. The study showed that the relative frequency of infestation by Sclerotium rolfsii and the number of viable sclerotia oscillate inversely and present a relative frequency of 45.7, 57.3, 42.3 and 49.5% for 2016, 2017, 2018, and 2019, respectively, and a number of sclerotia of 2.01, 1.65, 2.11 and 1.25 in 250 g of soil for 2016, 2017, 2018 and 2019, respectively. The study showed that the number of viable sclerotia was positively correlated with clay and silt content, soil pH, Mg, K, Fe, Cu, and Mn and negatively correlated with sand, SOM, EC, CaCO3, Zn, B, Ca, NH4 and NO3 contents. The observed decrease in viable sclerotia between 2016 and 2019 can be attributed to the decrease of Fe and Cu in the soil. It is possible that SOM intervenes with its humified fraction in the neutralization of the redox potential of Feand Cu which are involved in the production of sclerotia under oxidative stress. The good control of fertilization, especially organic, allows limiting the production of sclerotia of Sclerotium rolfsii. Data analysis allowed obtaining a significant prediction model of the number of viable sclerotia in the soil according to the physicochemical soil parameters with (R2 = 0.95 at P<0.0001) for only infested fields and (R2 = 0.87 at P<0.0001) for all the fields

Induced Systemic Resistance (ISR) in Arabidopsis thaliana by Bacillus amyloliquefaciens and Trichoderma harzianum Used as Seed Treatments

The Trichoderma fungal species and the bacteria Bacillus species were described as inducers of plant systemic resistance in relation to their antagonistic activity. The objective of this study was to evaluate the effect of selected strains of Bacillus amyloliquefaciens (I3) and Trichoderma harzianum (A) on inducing systemic resistance in Arabidopsis thaliana as a model for plant molecular genetics. The microorganisms were identified and were confirmed for their antagonistic potential in vitro and in vivo in previous studies. In order to explore this mechanism, two mutants of A. thaliana carrying a PR1 promoter (a conventional marker of salicylic acid (SA) pathway) and LOX2 promoter (a marker triggering jasmonic acid (JA) pathway activation) were analyzed after inoculating antagonists. Transgenic reporter line analysis demonstrated that B. amyloliquefaciens I3 and T. harzianum A induce A. thaliana defense pathways by activating SA and JA at a high level compared to lines treated with chemical elicitors of references (acibenzolar-S-methyl (Bion 50 WG (water-dispersible granule)), SA, and methyl jasmonate). The efficacy of B. amyloliquefaciens I3 and T. harzianum A in inducing the defense mechanism in A. thaliana was demonstrated in this study