RESUMEN
Cacao represents an important source of income for farmers in the south of Mexico. However, phytosanitary problems have disrupted the production over the years. The use of antagonistic microorganisms as biocontrol agents might improve the production of cacao. In this study, Paenibacillus polymyxa NMA1017, isolated from the rhizosphere of Opuntia ficus-indica L., was used as a biocontrol agent for black pod rot of Theobroma cacao L. cultivated in Chiapas, Mexico. The experiments were carried in vitro and in vivo using pear fruit (Pyrous communis) as model and cacao pods in the field, respectively. The effect of NMA1017 on the phytopathogen was observed by electron microscopy and the production of enzymes was tested as a potential mechanism of action. The bacterium inhibited the radial growth of Phytophthora tropicalis PtCa-14 by 85.9 ± 0.12%. The strain NMA1017 affected mycelial development, as observed by the damage to the cell wall of the oomycete. In pear fruit, the biocontrol agent controlled the production of mycelium on the pear fruit surface, indicating an inhibitory effect exerted. Cacao pods infected with P. tropicalis in the field resulted in a reduction in disease incidence from 86 to 33% and in infection from 68 to 6%. Moreover, strain NMA1017 produced hydrolytic enzymes such as cellulases, xylanases, chitinases and proteases. The results obtained highlight P. polymyxa NMA1017 as an organism of interest for the biocontrol of P. tropicalis, as a method to rescue this important crop in Mexico.
Asunto(s)
Cacao , Paenibacillus polymyxa , Phytophthora , México , Enfermedades de las Plantas/prevención & controlRESUMEN
Abstract Introduction: The organoleptic qualities of aromatic species and their derived products are directly related to some characteristics of flavor, color and nutritional value and depend largely on their genetic origin and content of secondary metabolites. Objective: The antioxidant activity of different genotypes of Theobroma spp. from Mexico was evaluated in order to distinguish promising qualities for genetic improvement, and to differentiate phylogenetic traits, considering biochemical variables. Methods: The amount of phenols, flavonoids and antioxidant activity was determined by ABTS and DDPH, in addition to the content of anthocyanins, theobromine and caffeine in four species of Theobroma L., and 50 genotypes derived from T. cacao. The results were analyzed using an analysis of variance, means test, principal component analysis and cladistic analysis. Results: There are highly significant differences between genotypes. The phenol content ranged from 7.5-85 mg g-1; flavonoids 6.57-69.6 mg g-1, antioxidant activity by ABTS of 17.3-86.1 and by DDPH of 40.0-53.3; anthocyanin content of 0.01-3, caffeine of 1.8-6.7-and theobromine of 2.9-9.8 mg g-1. Principal component and cladistic analysis helped explain the variation found and distinguish evolutionary characters and phylogenetic brotherhoods. The variation in content of phenols, flavonoids, antioxidant activity, anthocyanins, theobromine and caffeine was mainly due to the degree of domestication, while for the group of genotypes derived from T. cacao (forastero, trinitario and criollo) it was the origin of the seeds. Conclusions: The degree of domestication influences the content of phenols and antioxidant capacity. The results suggest that the evaluated variables can help to form criteria for genetic improvement in the complex derived from T. cacao oriented to the selection of higher phenol content and greater antioxidant activity.
Resumen Introducción: Las cualidades organolépticas de las especies aromáticas y sus productos derivados se relacionan directamente con algunas características del sabor, color y valor nutricional y dependen en gran medida de su origen genético y contenido de metabolitos secundarios. Objetivo: Se evaluó la actividad antioxidante de diferentes genotipos de Theobroma spp. de México, con el fin de distinguir cualidades promisorias para el mejoramiento genético, y diferenciar rasgos filogenéticos, considerando variables bioquímicas. Métodos: Se determinó la cantidad de fenoles, flavonoides y actividad antioxidante mediante ABTS y DDPH, además de contenido de antocianinas, teobromina y cafeína en cuatro especies de Theobroma L., y 50 genotipos derivados de T. cacao. Resultados: Los resultados fueron analizados mediante un análisis de varianza, prueba de medias, análisis de componentes principales y análisis cladístico. Existen diferencias altamente significativas entre genotipos. El contenido de fenoles varió de 7.5-85 mg g-1; flavonoides 6.57-69.6-mg g-1, actividad antioxidante por ABTS de 17.3-86.1 y por DDPH de 40.0-53.3; el contenido de antocianinas de 0.01-3, cafeína de 1.8-6.7 y teobromina de 2.9-9.8 mg g-1. El análisis de componentes principales y cladístico ayudó a explicar la variación encontrada y distinguir caracteres evolutivos y hermandades filogenéticas. La variación en contenido de fenoles, flavonoides, actividad antioxidante, antocianinas, teobromina y cafeína estuvo dada principalmente por el grado de domesticación, mientras que para el grupo de genotipos derivados de T. cacao (forastero, trinitario y criollo) fue el origen de las semillas. Conclusión: El grado de domesticación influye en el contenido de fenoles y actividad antioxidante. Los resultados sugieren que las variables evaluadas pueden ayudar a formar criterios para el mejoramiento genético en el complejo derivado de T. cacao orientado a la selección de mayor contenido de fenoles y mayor actividad antioxidante.