Septoria tritici blotch, caused by the fungal pathogen Zymoseptoria tritici, is a highly significant disease on wheat crops worldwide. The objective of the present study was to find out new bacterial strains with bio-antimicrobial activity against Z. tritici. Two phyllospheric bacteria (S1 and S6) were isolated from wheat ears and identified as Bacillus velezensis strains according to 16S rRNA Sanger sequencing. Antagonistic assays performed with either living strains or cell-free culture filtrates showed significant in vitro antifungal activities against Z. tritici. For the culture filtrates, the half-maximal inhibitory dilution and the minimal inhibitory dilution were 1.4% and 3.7% for the strain S1, and 7.4% and 15% for the strain S6, respectively. MALDI—ToF analysis revealed that both strains synthesize cyclic lipopeptides but from different families. Interestingly, only strain S1 produces putative bacillomycin D. Such differential lipopeptide production patterns might explain the difference observed between the antifungal activity of the culture filtrates of the two strains. This study allows the identification of new lipopeptide-producing strains of B. velezensis with a high potential of application for the biocontrol of Z. tritici.
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.
From our previous research of bio-control agents of the wheat pathogen Zymoseptoria tritici as an alternative to chemical control, one strain of Bacillus amyloliquefaciens and one strain of Trichoderma harzianum showed high antagonistic potential in vitro and in vivo as a foliar treatment on potted plants under greenhouse. The present work aimed to evaluate the antagonistic potential of these two strains of microorganisms in seed treatment. The results obtained showed that the two antagonists can reduce the severity of the disease assessed at three growth stages of the two wheat cultivars. B. amyloliquefaciens I3 reduced the severity of septoria leaf blotch by 56% and 58% compared to the checks on Aguilal and Karim respectively at the flag leaf stage, while in the case of T. harzianum A, this rate was 54% on Aguilal and 55% on Karim. These results suggest that the antagonistic potential is due to a distant mechanism of action such as induced systemic resistance. The viability tests of the two antagonists on coated seeds stored at 4 °C showed that they were viable after twelve months of conservation and preserved their antagonistic potential against Z. tritici.
In this chapter, the authors introduce two research axes: Part A, nano-biosensors as ad-hoc technologies designed to meet plant diagnostic sensitivity and specificity needs at point of care, and Part B, the study of the interaction of drought and infection stresses in crops investigating bio-control potential antagonists in developing integrated approach (IPM) for disease control measures in crops system. The first part will be revising most used nano-biosensors in plant pathogens detection using different platforms in greenhouses, on-field, and during postharvest. A special focus will be on optical and voltametric immuno/DNA sensors application in plant protection. The last part will present case studies of using nanoparticles functionalized with antibody/DNA for detecting pathogenic Pseudomonas sp, mosaic viruses, Botrytis cinereal, and Fusarium mycotoxins (DON). The second part will be interpreting experimental results of a case study on evaluating bio-control efficacy of local Trichoderma spp. using root dips treatment in Fusarium solani-green beans pathosystem as a model.
Sclerotium rolfsii Sacc. is a polyphagous fungus responsible for root rots of many cultivated crops. In Morocco, the fungus is responsible of important damages on sugar beet crop mainly in the Doukkala region. The aim of our study was to evaluate the antagonistic potential in vitro and in vivo of 191 bacterial isolates isolated from Moroccan soils and a bacterial strain from the laboratory collection Bacillus amyloliquefaciens referenced as I3, in the control of Sclerotium rolfsii. 14 of bacterial isolates showed antifungal activity against Sclerotium rolfsii. Isolates referenced as O4, E10 and E7 were the most efficient in vitro tests with an inhibition rate of the mycelial growth of Sclerotium rolfsii of 98.16%, 96.22% and 87.81%, respectively. The inhibition of sclerotia germination in soil by the bacterial suspensions varied from 85% to 95% for the aforementioned 3 isolates. The antifungal activity of the bacterial culture filtrates at proportions [1/2]; [1/3]; [1/4]; [1/10] ([Filtrate Volume /PDA Volume]) showed the ability of these bacteria to produce secondary metabolites capable of inhibiting Sclerotium rolfsii mycelial growth and sclerotia germination with inhibition percentages ranging from 30. 62% to 98.93% for mycelial inhibition and from 44.69% to 98.75% for sclerotia inhibition for isolate O4. The in vivo tests were performed by bacterization of seeds and the evaluation was done on 15 days old chickpea seedlings, statistical analysis revealed a very highly significant difference (p<0.05) between the isolates. Disease incidence was 7.5% with the T-O4 bacterized seeds and disease severity 30 days after inoculation was 20% for the most effective T-O4 treatment while the T control treatment had a severity of 89%. The isolates, isolated from Moroccan soils have shown their ability to inhibit Sclerotium rolfsii especially isolates O4 and E10.
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