Sueli Corrêa Marques de Mello

Potencial antagônico de Trichoderma spp. originários de diferentes agroecossistemas contra Sclerotinia sclerotiorum e Fusarium solani

From 40 soil samples collected in the Rio Grande do Sul, Minas Gerais, Sao Paulo, Bahia, Goias and Tocantins states, Brazil, a collection of 230 monosporic isolates of Trichoderma spp. was established using TSM selective media. In order to select efficient isolates for biological control, dual culture tests were carried out on PDA media at 20 oC for Sclerotinia sclerotiorum and at 25 oC for Fusarium solani f.sp. phaseoli. From the whole collection, 50 isolates presented antagonism against F. solani and 111 isolates to S. sclerotiorum. The antagonism against both pathogens was found in only 10% of the isolates. Scanning electron microscopy assessments with seven in vitro selected isolates showed that not all promoted hyperparasitism on the pathogens, suggesting the existence of other mechanisms of antagonism, as antibiosis or competition.

Controle de Fusarium oxysporum f.sp. phaseoli in vitro e em sementes, e promoção do crescimento inicial do feijoeiro comum por Trichoderma harzianum

Este trabalho objetivou avaliar seis isolados de Trichoderma harzianum no controle de Fusarium oxysporum f.sp. phaseoli em sementes, e seu efeito no crescimento inicial do feijoeiro comum. Os isolados foram inicialmente confrontados in vitro com o patogeno em testes de cultura pareada e antibiose a 25oC. Sementes sadias e artificialmente infectadas pelo patogeno foram microbiolizadas com 2 mL de suspensoes dos antagonistas (2,5 x 108 conidios mL-1) para cada 100 g de sementes, em rolo de papel germtest a 20 e 25°C. Os percentuais de incidencia do patogeno e de plântulas normais foram avaliados aos sete e nove dias, respectivamente. Em casa de vegetacao, os isolados foram aplicados a 5 x 109 conidios 500 g-1 de substrato autoclavado, com avaliacao do comprimento das raizes e parte aerea das plantas 11 dias apos o semeio (12 plantas tratamento-1). Todos os isolados apresentaram antagonismo in vitro contra o patogeno. Os isolados CEN202, CEN234, CEN238, CEN240 foram superiores a testemunha no controle de F. oxysporum em sementes, reduzindo entre 35 e 51% da incidencia do patogeno e proporcionando entre 73 e 81% de plântulas normais. O comprimento total das plantas com tratamento CEN239 (37,43 cm) foi superior aos demais, cujo comprimento variou entre 27,84 e 33,95 cm.

Molecular Markers for the Characterization of BrazilianCercospora caricis Isolates

Cercospora caricis is of interest as a potential mycoherbicide for control of purple nutsedge, Cyperus rotundus, which is considered to be the worlds worst weed. The genetic variation of a collection of Brazilian Ce. caricis isolated from Cy. rotundus was analyzed by using RAPD, RFLP with a telomeric probe, [TTAGGG]18 and sequencing of the ITS1-5.8S-ITS2 regions of the ribosomal RNA gene. The Brazilian isolates were also compared with a Ce. caricis isolate from Florida, USA and with some other Cercospora species. A cluster of isolates from the Brazilian cerrado region was identified showing high genetic similarity. In contrast, isolates originating in other geographic regions of Brazil were less than 50% and 25% related to the former group according to similarity estimates produced from RAPD and telomeric RFLP analyses respectively. ITS sequence analysis did not support taxonomic division of the Brazilian strains, but did confirm the distant relatedness of these strains to the Ce. caricis isolate from Florida. The data indicate a need for an extensive molecular survey of Cercospora species associated with the Cyperaceae.

Biological control of Fusarium oxysporum f. sp. phaseoli by Trichoderma harzianum and its use for common bean seed treatment

Biological control of seed-borne pathogens has shown to enhance germination and physiological quality of seeds. The objectives of this study were to evaluate the in vitro antagonistic effect of five Trichoderma harzianum isolates (CEN287, CEN288, CEN289, CEN290, and CEN316) against Fusarium oxysporum f. sp. phaseoli (Foxy) and test its potential use in seed treatment. Initially, pathogen and antagonists were grown in paired cultures at 25oC, from which samples were assessed using scanning electron microscopy (SEM). Then, clean or Foxy-infected seeds were treated with conidial suspension of the antagonists. Percent of Foxy-infected seeds and normal seedlings were evaluated at seven and nine days of incubation, respectively. All but one Trichoderma isolate (CEN290) inhibited Foxy mycelial growth. SEM analysis revealed that only one Trichoderma isolate (CEN287) showed parasitic interaction with Foxy. Two isolates (CEN287 and CEN316) significantly reduced the Foxy incidence and enhanced seed germination, though less effective than the fungicide mixture (carboxin + thiram). A principal component analysis indicated the importance of volatile metabolites in reducing Foxy incidence on common bean seeds. CEN287 Trichoderma harzianum isolate formed a single group due to its increase in germination rate of Foxyinfected seeds.

Produção de inóculo de Alternaria cassiae

In order to adjust the methodology of inoculum production, an isolate of the fungus Alternaria cassiae, selected as a biological control agent for sicklepod (Senna obtusifolia) was studied under different culture media and mycelial growth conditions. Homemade V-8 juice medium without CaCO3 addition, incubation on 200-250 mL of medium (around 50% of the flask volume) with agitation at 250 rpm during 48 hours, followed by mycelial mass growth in continuous dark were appropriate conditions for a large scale production of inoculum. The sporulation was aided by incubation of the mycelial mass at 25oC. The use of 300 mL of mycelial mass per pan (29.9 by 44.5 by 5.0 cm ) to induce the sporulation provided rapid dryness and ensured the conidium integrity, indicated by higher infectivity of the inoculum.

Isolados de Dicyma pulvinata em estromas de Microcyclus ulei em seringueira

Dicyma pulvinata is an efficient biocontrol agent of Microcyclus ulei, causal agent of South American leaf blight. The objective of this work was to obtain strongly antagonistic isolates. A survey was carried out in rubber plantations located in 14 municipalities in the Sates of Acre, Amazonas, Bahia, Mato Grosso, Para and Roraima, Brazil, obtaining 52 isolates of D. pulvinata. The antagonistic fungus was isolated on potato-dextrose-agar (PDA) plates and identified based on morphological characteristics of conidiophores and conidia, and colony appearance. The antagonic effect was tested by inoculating D. pulvinata on Fusicladium macrosporum lesions induced on rubber plants, previously. In order to maintain the morphological and pathogenic traits, fungus isolates were preserved by lyophilization, deep freeze (-80oC) and cryogeny. All isolates were introduced into Embrapa Recursos Geneticos e Biotecnologia fungus collection.

Reação de genótipos de maracujazeiro-amarelo ao Colletotrichum gloeosporioides

The present work was carried out in order to evaluate the resistance of passion fruit genotypes to C. gloeosporioides, the agent of anthracnose. C. gloeosporioides was inoculated in the lineages of passion fruit plants at a concentration of 5x106 spores on wounds pre-established by abrasion with a fine steel brush. The first evaluation was carried out 20 days after the inoculation and the others in intervals of seven days, ending in the seventh evaluation 62 days after the inoculation. To evaluate the degree of incidence and severity of anthracnose, a grade scale was established, where 1 = absence of symptoms and 7 = leaf loss. Average grades 2 and 3 and = Highly Susceptible (HS). In general, two genotypes were classified as Moderately Resistant; eight as Susceptible and sixty-two were highly Susceptible.

Molecular characterization of Brazilian Dicyma pulvinata isolates

Quarenta e nove isolados brasileiros de Dicyma pulvinata foram analisados quanto a caracteristicas morfologicas, analises de RFLP, RAPD e AFLP. Este fungo e um micoparasita do Microcyclus ulei, o agente causal da mais importante doenca da seringueira (Hevea brasiliensis), o mal-das-folhas. Estes isolados foram comparados com isolados indianos obtidos a partir de lesoes de Cercosporidium sp., com um isolado proveniente da Franca obtido a partir de lesoes de Cladosporium fulvum e com um isolado de D. ampullifera proveniente de Papua-Nova Guine. A analise de parâmetros morfologicos confirmou a identificacao dos isolados brasileiros. As representacoes graficas das matrizes de distância de cada marcador molecular mostraram resultados semelhantes. Os isolados de D. pulvinata obtidos de M. ulei mostraram-se intimamente relacionados. Por outro lado, os isolados - referencia, incluidos nestes estudos, mostraram-se bastante dispersos. De acordo com a analise de variância molecular, considerando todos os marcadores, os isolados de D. pulvinata obtidos de M. ulei, apresentaram diferenca significativa entre isolados procedentes de areas de cultivo de seringueira favoraveis a ocorrencia do mal-das-folhas (regioes norte e nordeste do Brasil) e aqueles de areas de escape da doenca (Mato Grosso).

Ação antagônica e de metabólitos bioativos de Trichoderma spp. contra os patógenos Sclerotium rolfsii e Verticillium dahliae

The antagonistic effect shown by fungi of the genus Trichoderma was assessed against the plant pathogens Sclerotium rolfsii and Verticillium dahlia, isolated from ornamental aster and strawberry, respectively. Twenty isolates of the antagonist were employed; they belonged to the species T. asperellum, T. hamatum, T. harzianum, T. koningiopsis, T. spirale and Trichoderma sp. Antagonism was investigated by means of dual culture tests and bioactive metabolite production based on the overlapping plate method. Most selected isolates had an inhibitory effect on the mycelial growth of S. rolfsii and V. dahlia, compared to controls. Except for non-volatile metabolite production tests, inhibitory action against V. dahliae was highest. Even the thermostable non-volatile metabolites showed inhibitory effect against both tested pathogens, evidencing that the secondary metabolites of the antagonist have a significant effect on these pathogenic species.

Compatibilidade de Dicyma pulvinata com defensivos agrícolas e eficiência do biocontrole do mal-das-folhas da seringueira em campo

The objective of this work was to evaluate four isolates of the antagonist fungus Dicyma pulvinata in terms of its compatibility with chemical pesticides and adjuvants products, and the efficiency of these isolates as biocontrol agent against South American leaf blight (Microcyclus ulei) of rubber tree (Hevea sp.) under field conditions. Isolates compatibility with chemical pesticides and adjuvants was evaluated on mycelial growth and fungus sporulation in vitro. To assess the efficiency of the antagonist against M. ulei under field conditions, the four isolates were compared to the control by the fungicide mixture propiconazol + mancozeb. The assays showed incompatibility of the antagonistic fungus with the fungicides benomyl, carbendazim, mancozeb, propiconazol, besides the insecticide-acaricide endosulfan. Two of the adjuvants tested did not affect the fungus development. It was demonstrated the action of D. pulvinata against M. ulei, in the field, especially for the isolates CEN 62 and CEN 93, which showed control levels similar to the fungicide standard treatment.