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Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/221194
Research and development of a new biocontrol agent against the foliar diseases downy and powdery mildews in cucurbit crops
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[eng] This doctoral thesis explores the initial phases of the development of a new phytosanitary product aimed at combating fungal diseases mildew (Pseudoperonospora cubensis) and powdery mildew (Podosphaera fusca) in cucurbit crops. The study began with the isolation and pre-selection of microbial species from different places and types of plants affected by one of these two diseases. This phase concluded with 724 microbial isolates (491 bacteria and 233 fungi). The selected strains were subjected to molecular screening for taxonomic classification by sequencing the 16S rRNA gene in bacteria and the ITS region in fungi. This process led to the identification of 128 bacterial strains of the desired group and 11 strains of the fungal species of interest. Efficacy trials against both pathogens, carried out under controlled conditions in cucumbers, showed that several isolates significantly reduced the severity of the disease. The most effective strains against one disease also showed high efficacy against the other. Among these, some strains of bacteria obtained the best preventive efficacy in both pathosystems and were selected for subsequent studies. In contrast, yeasts proved to be more effective as curative treatments for powdery mildew. The safety assessments of the five most effective strains were carried out based on the bioinformatics study of genome sequencing in accordance with EU regulatory requirements. Finally, only two bacterial strains were selected for further analysis as the most promising candidates. Their safety profiles were confirmed based on their taxonomic classification, the absence of plasmids or genetic motility elements associated with antimicrobial resistance, the lack of toxin genes or virulence factors, and the absence of dangerous metabolites. In addition, genes involved in the synthesis of beneficial secondary metabolites, such as surfactin and phengicin, were found in their genomes, which are very important for the efficacy of biocontrol. The production of these lipopeptides, along with other secondary metabolites, was subsequently validated by LC-QTOF-MS/MS analysis. In addition, in the evaluation of biofilm formation and leaf permanence, one of the two strains showed a superior biofilm formation capacity and environmental adaptability, especially in outdoor conditions, suggesting a greater potential for application in the field. Scanning electron microscopy also confirmed that this same strain formed more homogeneous biofilms with a mucous texture than the other previously selected strain. In summary, this work underlines the potential of biocontrol agents in sustainable agriculture, presenting the strain finally selected, based on a collection of 724 isolates, as a leading candidate for biocontrol products intended for the management of downy mildew and powdery mildew in cucurbits and possibly in other crops.
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BARCELÓ GENESTAR, Maria. Research and development of a new biocontrol agent against the foliar diseases downy and powdery mildews in cucurbit crops. [consulta: 4 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/221194]