Suchergebnisse

M. phaseolina é um dos patógenos habitantes de solo que causa grandes danos ao feijoeiro, portanto, estratégias que visam controlar o patógeno e promover maior resistência às plantas são requeridas. Sendo assim, o objetivo do estudo foi avaliar o efeito de Trichoderma spp., na forma de suspensão de conídios ou filtrado de cultura, no biocontrole de M. phaseolina e indução de resistência em feijoeiro. Para isso, foram realizados testes in vitro de confronto direto, metabólitos voláteis e de filtrado de cultura, utilizando cinco isolados de Trichoderma spp. e um isolado do patógeno. Ao final dos testes foi determinado o percentual de inibição do crescimento micelial do patógeno. Para os testes in vivo foram selecionados três isolados de Trichoderma spp., utilizando-os na forma de suspensão de conídios e filtrado de cultura para o tratamento das sementes. O patógeno foi inoculado via substrato por meio de grãos de arroz colonizados. Durante a condução do experimento foram realizadas avaliações da severidade da doença e coleta de material vegetal para as análises bioquímicas referentes à indução de resistência. Os resultados demonstram que Trichoderma spp. controlam M. phaseolina por meio dos mecanismos de parasitismo e antibiose, observados nos testes in vitro, bem como reduzem a severidade da podridão cinzenta do caule na cultura do feijão, pela indução de resistência e pela melhoria no enfrentamento as espécies reativas de oxigênio causadas pelo ataque do patógeno, identificado pela potencialização da atividade das enzimas superóxido dismutase e guaiacol peroxidase.
Palavras-chave: Phaseolus vulgaris. Superóxido Dismutase. Guaiacol Peroxidase. Peróxido de Hidrogênio.
Abstract
M. phaseolina is one of soil-inhabiting pathogens that cause great damage to bean plants, therefore, strategies that aim to control the pathogen and promote greater plant resistance are necessary. Therefore, the objective of the study was to evaluate the effect of Trichoderma spp., in the form of conidial suspension or culture filtrate, on the biocontrol of M. phaseolina and induction of resistance in bean. For this, in vitro tests of direct confrontation, volatile metabolites and culture filtrate tests were carried out, using five isolates of Trichoderma spp. and an isolate of the pathogen. At the end of the tests, the percentage of inhibition of mycelial growth of the pathogen was determined. For in vivo tests, three isolates of Trichoderma spp. were selected, using them in the form of conidial suspension and culture filtrate for seed treatment. The pathogen was inoculated via substrate through colonized rice grains. During the experiment, assessments of the severity of the disease were carried out and plant material was collected for biochemical analyzes related to the induction of resistance. The results demonstrate that Trichoderma spp. control M. phaseolina through the mechanisms of parasitism and antibiosis, observed in in vitro tests, as well as reduce the severity of gray stem rot in bean crops, by inducing resistance and improving the fight against reactive species of toxicity caused by the pathogen attack, identified by the activity potentiation of the enzymes superoxide dismutase and guaiacol peroxidase.
Keywords: Phaseolus vulgaris. Superoxide Dismutase. Guaiacol Peroxidase. Hydrogen Peroxide.

Due to the increase in pecan nuts demand, plantation areas are expanding around the world and more frequent epidemics caused by fungal pathogens may occur in orchards and nurseries. Ragnhildiana diffusa is a pathogenic fungus reported to cause brown leaf spots on pecans in numerous countries. The scarcity of comprehensive information in symptoms on the host and morphology of the fungus lead this disease to be initially incorrectly identified in Brazil. In this study, we employed different approaches to characterize the pathogen morphology and pathogenicity and to molecularly identify the organism causing brown leaf spots in southern Brazil. A phylogenetic analysis based on the internal transcribed spacer (ITS) and the large subunit (LSU) gene sequences confirmed R. diffusa as the causal pathogen of the disease. Inoculation tests on healthy leaflets confirmed pathogenicity isolates, although some variation in their virulence was observed. Variation in the morphology of the asexual stage was observed among and within isolates. This study brought unprecedented morphological, genetic and pathogenic information that aids elucidating the disease. The accurate and prompt identification of the disease may assist in controlling further spread of the pathogen into orchards and nurseries still free of the disease in South America.