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Thesis (Ph.D.)--University of California, Berkeley, 1961. / "UC-48 Biology and Medicine" -t.p. "TID-4500 (16th Ed.)" -t.p. Includes bibliographical references (p. 75-80).

Thèse--Faculté des sciences de Paris.

Made available in DSpace on 2014-06-11T19:32:54Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-10-27Bitstream added on 2014-06-13T20:44:15Z : No. of bitstreams: 1 rosa_mm_dr_rcla.pdf: 4775636 bytes, checksum: 3a910249e344253877ee9051e3958b03 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / As leveduras são microrganismos importantes em diferentes processos biotecnológicos, sendo amplamente empregadas industrialmente. Apesar de se apresentarem em grande número em ambientes naturais, como na superfície de plantas (folhas, flores e frutos) e na rizosfera, pouco é conhecido sobre sua função nestes habitats. O controle de fitopatógenos tem sido estudado como um potencial papel das leveduras, principalmente inibindo fungos que causam podridões em frutas no período pós-colheita, e controlando doenças de diversas culturas de interesse econômico no campo, pois são ótimas competidoras por nutrientes e espaço. Neste contexto, o objetivo do presente trabalho foi isolar, avaliar e caracterizar leveduras de áreas agrícolas quanto ao controle de fungos fitopatogênicos in vitro e in vivo. Foram isoladas mais de uma centena de linhagens de leveduras, as quais foram avaliadas inicialmente quanto ao antagonismo à três fungos fitopatogênicos (Colletotrichum sublineolum, Colletotrichum graminicola e Thielaviopsis paradoxa) em testes in vitro. Os isolados com comportamento antagônico foram identificados através do sequenciamento da região ITS do rDNA e por fingerprinting utilizando-se a técnica de ISSR (Inter Simple Sequence Repeats). Foram realizados testes de antagonismo em meios de cultura sólidos (pela avaliação do crescimento micelial do fitopatógeno) e líquidos (pela avaliação da germinação dos esporos fúngicos), além de experimentos in vivo em plantas de sorgo e toletes de cana-de-açúcar, verificando-se o controle das doenças antracnose e podridão abacaxi, respectivamente. Foram realizadas análises para detecção de possíveis mecanismos de ação das leveduras, como competição por nutrientes; produção de toxina killer, compostos voláteis, enzimas hidrolíticas e sideróforos, além da avaliação de possíveis danos causados pela levedura... / The yeasts are important microorganisms for different purposes in biotechnological processes and widely utilized industrially. Although in high numbers in natural environments, as plant surfaces (leaves, flowers and fruits) and rhizosphere, a little is known about their functions in the habitats. The control of phytopathogens by the yeasts has been studied, mainly inhibiting molds which cause fruit rots in the postharvesting period, and controlling diseases of economically important cultures in the field, once they are good competitors for nutrients and space. In this context, the aim here is the isolation, screening and characterization of yeasts from agricultural areas regarding their ability to control phytopathogenic molds in vitro and in vivo. More than a hundred of strains were isolated, which were initially screened for the in vitro antagonism against three phytopathogenic molds (Colletotrichum sublineolum, Colletotrichum graminicola and Thielaviopsis paradoxa). The isolates with antagonistic behavior were identified by the sequencing of ITS region in the rDNA and by fingerprinting with the ISSR (Inter Simple Sequence Repeats) technique. Antagonism tests in solid media (evaluating the mycelial growth of the phytopathogen) and liquid media (evaluating the fungal spore germination) were carried out, besides in vivo experiments with sorghum and sugar cane to verify the control of anthracnose and pineapple disease, respectively. Mechanisms of action by yeasts towards the molds were evaluated as competition for nutrients; production of killer toxin, volatile compounds, hydrolytic enzymes and siderophores. The damage caused by the yeast in the fungal hyphae was also approached. The results indicated three yeast species with good results as antagonists (Torulaspora globosa, Candida intermedia and Rhodotorula mucilaginosa). All the yeasts exhibited antagonism against the phytopathogenic... (Complete abstract click electronic access below)

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