Incidência e transmissão de dsRNA em Pseudocercospora griseola, agente causal da mancha-angular do feijoeiro comum (Phaseolus vulgaris)

• Autor(a) principal: Lima, Swiany Silveira
• Data de Publicação: 2008
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/5300
• topic: Micovírus; Pseudocercospora griseola; Phaeoisariopsis griseola; Mycovirus; Pseudocercospora griseola; Phaeoisariopsis griseola; CNPQ::CIENCIAS BIOLOGICAS::GENETICA::GENETICA MOLECULAR E DE MICROORGANISMOS

The common bean Phaseolus vulgaris shows great importance under feeding and economical aspects for the Brazilian people. However, its productivity has been low due to the occurrence of diseases and other factors. The angular leaf spot is distinguished among those diseases. Its causal agent is the Pseudocercospora griseola (Sacc.) Crous & U. Braun. Some mycovirus or virus-like particles were already described in several phytopathogenic fungus. Those viruses are unable to penetrating and lysing the host cells, and the intracytoplasmic transmission is accomplished by anastomosis among hyphae and the sporogenesis. Most mycovirus are found as multiple dsRNA fragments. In general, the mycovirus are cryptic (latent) concerning to the effects caused into phenotype of the host fungus, but they can affect the biology of their host by provoking morphological changes, hyper or hypovirulence. Because they are associated to the hypovirulence phenomenon, the mycoviruses show a potential use in the biocontroll of the phytopathogenic fungus. The general objective of this work was to characterize the mycovirus in the isolates of P. griseola, since they were recently detected in this fungus species for the first time. To reach this objective, the following were performed: the characterization of the dsRNA in different isolates; the vertical transmission analysis; and the obtainment of isogenic lines by the virus cure. The dsRNAs were detected in 31 from those 49 isolates of P. griseola under analysis. In the present study, most isolates showed multiple dsRNA fragments varying from zero to 10, as being the sizes estimated between 0.8 and 4.8 kb. The dsRNA fragment of 4.8 kb from the isolate was efficiently transmitted to the asexual spores. However, not all dsRNA fragments (between 1 and 6) found in the isolate Ig848 were transmitted to monosporic colonies. The cycloheximide was used at concentration of 20 µg/mL in order to obtain the mycovirus cure. This treatment was ineffective for the isolate 29-3, since those three colonies transplanted to cyclohexymide during four generations showed the same profile as the total nucleic acids found in the wild isolate. In the case of the isolate Ig848, this same chemical treatment eliminated the fragments 2.2; 2.0; 1.8; 1.2 and 1.0 kb of the colonies Ch2 and Ch4 after seven successive transplantings in medium containing cycloheximide. Several phytopathogenic fungus are attacked by viral infections, and this variation in the profile of the nucleic acid found in the P. griseola isolates is also observed in other plant pathogens. The presence of multiple fragments in only one isolate may be due to the infection by virus with segmented genome, RNA satellite, defective RNA or mixed infections. The efficiency of the transmission by conidia is variable, as depending on the fungus species under consideration, but it is usually near 100% as occurred for the isolate 29-3 of P. griseola. Either cure of some dsRNA fragments and the spontaneous loss during conidiogenesis observed for the isolate Ig848 rather indicate the infection by independent replicons. In those isogenic lines with and without some dsRNA fragments, the effect of the viral infection will be evaluated under some aspects such as the sporulation rate, growth and pathogenicity. The characterization of those viruses found in P. griseola will allow for further studies concerning to their use in the biological control of the angular leaf spot, which will turn possible to reduce the economical losses caused by this disease in agriculture.