Biocaracterização de procariotas como agentes de biocontrole de enfermidades e como promotores de crescimento em feijoeiro

• Autor(a) principal: Garcia, Flávio Augusto de Oliveira
• Data de Publicação: 2008
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1022
• topic: Feijão; Doenças e pragas; Controle biológico; Bacillus cereus; Pseudomonas putida; Phaseolus vulgaris; Bean; Diseases; Biological control; Bacillus cereus; Pseudomonas putida; Phaseolus vulgaris; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::FITOPATOLOGIA

Brazil is the most important bean producer in the world (3 million tons per year). This productivity could be higher but several impairing factors exist and one of them is the continuous occurrence of diseases along the crop cycle. More than one hundred pathogens have been reported causing diseases in beans and the common bacterial blight, angular spot, rust and anthracnose are the most important aerial part diseases in Brazil bringing about losses as large as 50% under ideal conditions for disease incidence. Control measures for the aforementioned diseases do not present good efficacy mostly due low efficiency of chemicals along with the high pathogen variability. Therefore, the possibility of biological control turns into an actual alternative for the integrated management of diseases. Among organisms under investigation, rhizobacteria as well as bacterial endophytes and prokaryotic phylloplane residents have shown good potential for the biocontrol. The main purpose of this dissertation was to evaluate the ability of five prokaryotes, being three isolates of Bacillus cereus (isolates UFV-172, UFV-101 and UFV-075) and two isolates of Pseudomonas putida (isolates UFV-053 and UFV-Pp) as biocontrol agents for aerial part diseases in beans as well as to investigate the possible mechanisms involved in the observed biocontrol and to monitor populational tendencies of the biocontrol agents in bean phylloplane. Greenhouse assays, with replicates in time and in space, along a whole year, indicated that the organisms were efficient for controlling the common bacterial blight (Xanthomonas axonopodis pv. phaseoli). In terms growth- promoting ability, isolates UFV-172 and UFV-075 proved to be efficient, either in a greenhouse or in field trials. Investigation on mechanisms on the observed biological control, it was found that the five organisms were inducers of systemic resistance in bean plants, there were increases in the activity of the so called indicator enzymes of the induced state, as well as effective biocontrol of the common bacterial blight even after spatial separation of the microbial components of the interaction. In a standard bioassay with soybean cotyledons, isolates UFV-172 and UFV-075 of Bacillus cereus (viable cells, cell extracts and supernates of liquid cultures) were able to act as elicitors of the phytoalexin glyceollin that is known as a product of activated mechanisms of induced resistance in soybean. In two bioassays, it was observed the occurrence of biocontrol mechanisms such as competition for ecological niches and for nutrients, in the case of the tested isolate UFV-172. In a field experiment, the simultaneous deliver of isolates UFV-075 and UFV-053 did not improve the efficiency of isolates delivered separately, for the biocontrol of bean rust (Uromyces appendiculatus). A field assay, repeated twice in time along a given year, it was observed the efficiency of all five isolates for promoting the biocontrol of the angular leaf spot (Pseudocercospora griseola).