Loading...
7 results
Search Results
Now showing 1 - 7 of 7
- Potencialidades da utilização de fungos na luta biológica de Colletotrichum acutatumPublication . Baptista, Paula; Coelho, Valentim; Pereira, Eric Carvalho; Bento, Albino; Pereira, J.A.A gafa é considerada a doença mais importante do olival em Portugal, podendo em algumas das situações originar perdas de 100% dos frutos. Diferentes trabalhos evidenciaram que a nível nacional o principal agente patogénico associado a esta doença é o fungo Colletotrichum acutatum. Neste sentido, no presente trabalho pretendeu-se estudar o potencial antagonista de dois isolados fúngicos, provenientes da micoteca da Escola Superior Agrária do Instituto Politécnico de Bragança, nomeadamente Hypholoma fasciculare e Trichothecium roseum, contra C. acutatum, de forma a avaliar a sua possível utilização na luta biológica contra esta doença. O primeiro isolado fúngico trata-se de uma espécie macrofúngica saprófita-lenhícola usado como agente de luta biológica no controlo de patogénicos; enquanto o segundo é uma espécie descrita como produtor de metabolitos antifúngicos (Trichothecin). O estudo foi efectuado em condições in vitro através do estabelecimento de co–culturas em meio Melin-Norkrans gelificado, pH 6,6. Os valores dos raios (interno, na região inter-inóculos e externo, na regiões diametralmente opostas) das colónias fúngicas foram determinados durante dez dias. Ambas as espécies fúngicas estudadas inibiram significativamente o crescimento de C. acutatum na região inter-inóculos. As reduções de crescimento por H. fasciculare foram de 16,4% (raio interno) e de 27,4% (raio externo). T. roseum inibiu somente o crescimento de C. acutatum na zona inter-inóculos em 19,0%. De entre os fungos estudados, H. fasciculare foi o que originou uma maior percentagem de inibição de crescimento de C. acutatum, apresentando valores significativamente superiores face a T. roseum ao nível do raio externo. O efeito inibitório no crescimento de C. acutatum ocorreu muito antes de se ter estabelecido qualquer contacto físico entre as colónias, sugerindo que o mecanismo antagonista adoptado pelo H. fasciculare e T. roseum seja do tipo “antagonismo à distância”. Os resultados obtidos podem abrir novas perspectivas na luta biológica contra a gafa da oliveira pela utilização destas duas espécies fúngicas.
- Effect of competitive interactions between ectomycorrhizal and saprotrophic fungi on Castanea sativa performancePublication . Pereira, Eric Carvalho; Coelho, Valentim; Tavares, Rui Manuel; Lino-Neto, Teresa; Baptista, PaulaIn Northeast of Portugal, the macrofungal community associated to chestnut tree (Castanea sativa Mill.) is rich and diversified. Among fungal species, the ectomycorrhizal Pisolithus tinctorius and the saprotroph Hypholoma fasciculare are common in this habitat. The aim of the present work was to assess the effect of the interaction between both fungi on growth, nutritional status, and physiology of C. sativa seedlings. In pot experiments, C. sativa seedlings were inoculated with P. tinctorius and H. fasciculare individually or in combination. Inoculation with P. tinctorius stimulated the plant growth and resulted in increased foliar-N, foliar-P, and photosynthetic pigment contents. These effects were suppressed when H. fasciculare was simultaneously applied with P. tinctorius. This result could be related to the inhibition of ectomycorrhizal fungus root colonization as a result of antagonism or to the competition for nutrient sources. If chestnut seedlings have been previously inoculated with P. tinctorius, the subsequent inoculation of H. fasciculare 30 days later did not affect root colonization, and mycorrhization benefits were observed. This work confirms an antagonistic interaction between ectomycorrhizal and saprotrophic fungi with consequences on the ectomycorrhizal host physiology. Although P. tinctorius is effective in promoting growth of host trees by establishing mycorrhizae, in the presence of other fungi, it may not always be able to interact with host roots due to an inability to compete with certain fungi.
- Tolerance and stress response of Macrolepiota procera to nickelPublication . Baptista, Paula; Ferreira, Sílvia; Soares, Maria Elisa; Coelho, Valentim; Bastos, Maria de LourdesNickel (Ni) is an essential element for many organisms; however, it is very toxic at high concentrations and also depending on the species. In macrofungi the mechanisms underlying their Ni tolerance are poorly documented. This study examines, for the first time, the participation of the antioxidative system in Macrolepiota procera exposed to different Ni2+ concentrations and their relation with Ni tolerance. The effect of the pH on Ni tolerance was also evaluated. The fungus was cultivated on solid medium with different NiCl2 concentrations (0.05, 0.2, 0.8 mM) at pH 4, 6, and 8, and fungi growth and Ni uptake were determined. The antioxidative enzymes catalase (CAT) and superoxide dismutase (SOD) and the production of hydrogen peroxide (H2O2) were evaluated on fungal submerged cultures within the first hours of Ni2+ exposure. Results showed that M. procera growth decreased when Ni2+ concentrations increased, reaching a maximum growth inhibition (>80%) up to 0.2 mM of NiCl2. Ni uptake increased proportionally to Ni increase in the medium. Both Ni tolerance and Ni accumulation were affected by medium pH. Microscope observations showed differences in the size of spores produced by fungi at different Ni concentrations. Ni exposure induced oxidative stress, as indicated by the production of H2O2, the levels of which seem to be regulated by the antioxidant enzymes SOD and CAT. The time variation pattern of SOD and CAT activities indicated that the former has a greater role in alleviating the stress. The results obtained suggested that tolerance of M. procera to Ni2+ is associated with the ability of this macrofungus to initiate an efficient antioxidant defense system
- Intraspecific variation of the entomophatogenic fungi Beauveria bassiana collected in olive groves from different geographic origin.Publication . Coelho, Valentim; Baptista, Paula; Bento, Albino; Lino-Neto, Teresa; Santiago-Álvarez, C.; Quesada-Moraga, Enrique; Pereira, J.A.The fungus Beauveria bassiana is a well recognised entomopathogen known to infect hundreds of host species from most of the insect orders. Therefore, the use of this fungus as a biological control agent against insect pests is very promising and several commercial products have already been developed. The natural occurrence of B. bassiana has been reported throughout Spain. Recently, its presence has been also verified in Portugal, specifically in the Trás-os-Montes region.
- Beauveria bassiana, fungo entomopatogénico da traça-da-oliveira em Trás-os-Montes: caracterização morfológica e molecular.Publication . Baptista, Paula; Coelho, Valentim; Bento, Albino; Lino-Neto, Teresa; Pereira, J.A.A traça-da-oliveira, Prays oleae (Bern.), é uma praga chave da oliveira na região de Trás-os-Montes. Uma possível alternativa à luta química contra esta praga, reside na utilização de fungos entomopatogénicos (FE). Contudo, a presença e expressão destes fungos em Portugal é praticamente desconhecida. Recentemente Introdução e objectivos foi efectuado o isolamento in vitro de fungos, associados a pupas de traça-da-oliveira parasitadas, provenientes de olivais localizados na região de Trás-os-Montes. No presente trabalho pretendeu-se caracterizar morfologicamente e molecularmente um dos isolados obtidos – Beauveria bassiana.
- Beauveria bassiana, fungo entomopatogénico da traça-da-oliveira em Trás-os-Montes: caracterização morfológica e molecular.Publication . Baptista, Paula; Coelho, Valentim; Bento, Albino; Lino-Neto, Teresa; Pereira, J.A.A traça-da- olivelra, Prays oleoe (Bern.), é uma praga chave da oliveira na região de Trás- os-Montes. Uma possível alternativa a luta química contra esta praga, reside na utilização de fungos entomopatogénicos (FE). Dado o desconhecimento da presença e expressão destes fungos em Portugal foi recentemente efectuado o isolamento in vitro de fungos, associados a pupas de traça-da-oliveira parasitadas, provenientes de olivais localizados na região de Trás- os-Montes. No presente trabalho pretendeu-se caracterizar morfologicamente e molecularmente um dos isolados obtidos.
- Scavenging capacity of strawberry tree (Arbutus unedo L.) leaves on free radicalsPublication . Oliveira, Ivo; Coelho, Valentim; Baltasar, Raquel; Pereira, J.A.; Baptista, PaulaDespite strawberry tree (Arbutus unedo L.) leaves had a long use in traditional medicine due to its antiseptic, diuretic, astringent and depurative properties, the potential of their antioxidant activity are still lacking. Our study goals to assess the antioxidant and free radical scavenging potential of water, ethanol, methanol and diethyl ether extracts of A. unedo leaves. Total phenols content was achieved spectrophotometrically using Folin–Ciocalteau reagent with gallic acid as standard. Antioxidant activity was evaluated using three different methods: reducing power of iron (III)/ferricyanide complex assay, scavenging effect on DPPH (2,2-diphenyl-1-picrylhydrazyl) radicals and scavenging effect on superoxide radicals by using the PMS–NADH–nitroblue tetrazolium system. Ethanol extracts of A. unedo leaves were the highest in reducing power (IC50 232.7 lg/mL) and DPPH scavenging effect (IC50 63.2 lg/mL) followed by water extracts (with IC50 of 287.7 and 73.7 lg/mL, respectively); whereas diethyl ether extracts were the lowest. In the scavenging on superoxide radical assay, methanol extracts obtained the best results (IC50 6.9 lg/mL). For all the methods tested the antioxidant activity was concentration dependent. In accordance with antioxidant activity, highest total phenols content were found in ethanol, followed by water, methanol and diethyl ether extract. The results indicated that A. unedo leaves are a potential source of natural antioxidants.