Plant extracts to control Alternaria alternata in Murcott tangor fruits

Background: Alternaria alternata causes the Alternaria brown spot disease (ABS) in many tangerines and their hybrids worldwide. Plant extracts offer an alternative method for controlling this disease, which control is based on chemical fungicides. Aims: To identify plant species with antifungal properties against A. alternata, the causal agent of the ABS. Methods: Plant extracts prepared from leaves, barks, flowers, and stalks collected from 105 plant species in the State of Minas Gerais, Brazil, were tested for activity against the fungus A. alternata in vitro and in vivo. Results: The most promising extract was obtained from Anadenanthera colubrina, which reduced the disease on Murcott tangor fruits to levels obtained with commercial fungicides. Artemisia annua, Cariniana estrelensis, Ficus carica, and Ruta graveolens presented moderate in vitro antifungal activity, but no effects were observed on the disease when the extracts were applied to fruits inoculated with the fungus. Besides, A. colubrina was the most active extract against A. alternata in the in vitro assay. Conclusions: The results obtained in the in vitro and in vivo assays suggested that the fungal growth test, which uses 96-well polypropylene plates, seems to be appropriate for selecting potential plant species for testing new methods to control ABS.Original Abstract: Antecedentes: Alternaria alternata causa la mancha marron en muchas mandarinas y en sus hibridos en todo el mundo. Extractos de plantas proporcionan un metodo alternativo para controlar esta enfermedad cuyo control se basa en fungicidas quimicos. Objetivos: Identificar las especies de plantas con propiedades antifungicas contra A. alternata, el agente causal de la mancha marron. Metodos: Extractos de plantas preparados a partir de hojas, corteza, flores y tallos recogidos de 105 especies de plantas en el Estado de Minas Gerais, Brasil, fueron utilizados para estudiar su actividad contra el hongo A. alternata in vitro e in vivo. Resultados: El extracto mas prometedor se obtuvo de Anadenanthera colubrina, que redujo la enfermedad en las frutas de tangor Murcott a los niveles obtenidos con fungicidas comerciales. Artemisia annua, Cariniana estrelensis, Ficus carica y Ruta graveolens presentaron moderada actividad antifungica in vitro, pero no se observaron efectos sobre la enfermedad cuando los extractos fueron aplicados a los frutos inoculados con el hongo. Ademas, A. colubrina fue el mas activo contra A. alternata en el ensayo