Óleos essenciais no controle de fungos causadores da podridão no caudex na rosa-do- deserto (Adenium Obesum): toxicidade, seletividade e modo de ação

Abstract

Essential oils (EOs) contain secondary metabolites with potential application in the sustainable control of phytopathogens, representing an alternative to synthetic fungicides. This study investigated the antifungal activity of essential oil from holy basil (Ocimum tenuiflorum) through experimental and computational approaches, aiming to understand its efficacy and possible mechanisms of action. Initially, the target pathogens were characterized based on morphological, molecular, and pathogenicity aspects. The analyzed isolates were identified as Fusarium spp. and Neocosmospora keratoplastica, and were confirmed as causal agents of caudex rot in desert rose plants. In vivo assays evaluated the efficacy of the EO in preventive and curative applications. Preventive treatment showed greater efficiency, with a significant reduction in the area under the disease progress curve (AUDPC) as concentration increased, reaching values close to zero at the highest tested doses. These results indicate the oil’s protective capacity and possible interference in the early stages of pathogen infection and colonization. In curative treatments, although disease severity was reduced with increasing concentration, the effect was less pronounced, suggesting limited ability to reverse already established infections. Assessments on non-target organisms revealed that the EO also exhibits antimicrobial activity against bacilli, highlighting the importance of selectivity and environmental impact studies. To investigate the mechanisms of action, structural modeling and molecular docking approaches were applied to essential fungal proteins, including lanosterol 14α-demethylase (CYP51A) and the α/β-tubulin heterodimer. The three- dimensional models showed high reliability, validated by metrics such as pLDDT, predicted aligned error (PAE), and Ramachandran analysis. Modeling of the heme group in CYP51A revealed axial coordination with a conserved cysteine residue, consistent with the functional architecture of fungal cytochrome P450 enzymes. Molecular docking with 27 ligands identified in the EO revealed different affinities toward the targets. Overall, CYP51A exhibited more favorable binding energies, particularly with hydrophobic sesquiterpenes such as dehydroaromadendrane, which showed deep binding and predominantly hydrophobic interactions near the heme group. Smaller compounds, such as 1,8-cineole, displayed intermediate affinity, while eugenol showed mixed interactions, including hydrogen bonding and unfavorable steric contacts, explaining its lower stability within the active site. In α/β- tubulin, the sesquiterpene α-copaene presented the best estimated affinity, fitting deeply into the colchicine binding site (CBS) and establishing extensive hydrophobic contacts at the heterodimer interface. Taken together, the experimental and computational results indicate that EO compounds may act through multiple mechanisms, including interference with ergosterol biosynthesis and microtubule dynamics. This thesis contributes to the understanding of the mechanisms of action of natural metabolites and to the rational prospecting of bioactive molecules with potential application in the sustainable management of fungal diseases of agricultural importance.