RESUMO
Cinnamic acid and geraniol are two well-known antifungal natural products and widely applied in food and cosmetics industries. To discover novel natural product-based fungicide candidates with more potent activity and good ecological compatibility for the management of plant diseases, a series of cinnamic acid-geraniol hybrids were prepared by means of molecular hybridization and their chemical structures were well confirmed by spectral analysis. The antifungal activities of the target compounds against three phytopathogenic fungi Fusarium graminearum, Gaeumannomycesgraminis (Sacc.) Arx et Oliver var. tritici (Sacc.) Walker, and Valsa mali were evaluated. Among them, compounds 5e and 5f showed the remarkable antifungal activity against G. graminis with the EC50 values of 82.719 and 91.828 µg/mL, respectively; while compounds 5f and 6b exhibited the obvious antifungal activity against V. mali. It suggested that compound 5f can be further optimized for the design of novel broad-spectrum fungicide molecules as the secondary lead compound. In addition, some interesting structure-antifungal activity relationships were obtained. This work will provide some reference and guidance for the further discovery of novel fungicide candidates based on cinnamic acid and geraniol.
RESUMO
Tree peony black spot (TPBS), mainly caused by Alternaria suffruticosae, is a common leaf disease on the ornamental peony, which poses a great threat to the flower buds in the current year and the flowering quality in the next year. However, there is only one fungicide registered for the control of this disease, difenoconazole. In order to avoid the severe problem of pathogen resistance caused by long-term use of difenoconazole, it is necessary to screen more chemical fungicides for the prevention and control of TPBS. In this study, the biological activities of flutolanil, phenamacril, pyraclostrobin, and boscalid on mycelial growth, conidial germination, germ tube elongation, and sporulation quantity of A. suffruticosae were determined, and the field control efficacy was tested to evaluate the preventive and therapeutic activities. Difenoconazole was used as a control simultaneously. The results showed that pyraclostrobin had the strongest inhibitory effects on the conidial germination, mycelium growth, germ tube elongation, and sporulation quantity, with the average EC50 values of 0.0517, 0.5343, 0.0008, and 0.8068 µg/ml, respectively. The inhibitory activity of flutolanil on the four developmental stages of A. suffruticosae was weaker than that of the other three fungicides. Compared with flutolanil, boscalid, the other succinate dehydrogenase inhibitor, had more strong inhibitory effects on the mycelial growth and sporulation quantity, with the average EC50 values of 3.8603 and 1.4760 µg/ml, respectively. Phenamacril had a moderate inhibitory level and had more inhibitory activity on conidial germination and germ tube elongation, with the average EC50 values of 31.5349 and 5.2597 µg/ml, respectively. All of the four fungicides had no significant effects on the shape of spores and germ tubes. The control fungicide difenoconazole had the strongest inhibitory activity on mycelial growth, and the average EC50 value was only 0.3297 µg/ml. However, its inhibitory activity on the other three growth stages was not high. In the field trials, pyraclostrobin had high control efficacy on TPBS even at low concentrations, reaching a minimum of 62.6293%, which was higher than that of difenoconazole. The other three fungicides had higher control efficacy at high concentrations but decreased significantly at low concentrations. Considering the dosage and control efficacy, pyraclostrobin was the first choice for the control of TPBS. Pyraclostrobin is the preferred alternative fungicide to difenoconazole for the prevention and control of TPBS in production.