Browsing by Author "Mina, Diogo"
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- Ação antagónica e mecanismo de ação de um isolado bacteriano contra o agente causal da tuberculose da oliveiraPublication . Santos Júnior, José Mendes dos; Mina, Diogo; Pereira, J.A.; Rodrigues, Tatiana Tozzi Martins Souza; Baptista, PaulaA oliveira (Olea europaea L.) é atualmente cultivada em quase todo o mundo. É, contudo, na bacia do Mediterrâneo que o seu cultivo está centrado representando cerca de 95% da superfície oleícola mundial (GOMES ET AL., 2012). Esta cultura possui grande importância econômica, sobretudo, em função dos seus frutos, que podem ser utilizados tanto para a produção de azeitona de mesa, como para a produção de azeite de oliva (TORRES et al., 2007; GONÇALVES, 2014). Entre algumas doenças que podem acometer a planta está a tuberculose-da-oliveira, ocasionada pela bactéria Pseudomonas savastanoi pv. savastanoi (Psv). A sintomatologia manifesta-se na geração de tumores (nódulos), sobretudo nos troncos e ramos (QUESADA et al., 2010). Na natureza, os microrganismos, incluindo as bactérias, vivem, na sua maioria, em comunidades. Nelas, os microrganismos estabelecem complexas interações que podem ser colaborativas ou competitivas (FREILICH et al., 2011). No caso particular da tuberculose, foi verificado recentemente que algumas bactérias não patogênicas, pertencentes aos gêneros Pantoea, Erwinia e Curtobacterium, e, frequentemente, associadas ao Psv nos nódulos colaboram com o patogênico aumentando a severidade da doença (BUONAURIO et al, 2015). Na atualidade, não existe nenhum método que permita erradicar a tuberculose. Estudos prévios por nós efetuados possibilitaram a identificação de uma bactéria (Bacillus En40) com capacidade de inibir, em condições in vitro, o crescimento de Psv. O presente trabalho tem por objetivo estudar o efeito antagonista deste isolado bacteriano contra as bactérias Pantoea agglomerans (Pa), Erwinia oleae (Er), Curtobacterium flaccumfaciens (Cu) e Psv, isoladamente, e em vários consórcios. Adicionalmente, pretende-se avaliar os mecanismos antagonistas exibidos pelo isolado bacteriano Bacillus En40 através da análise da produção de enzimas líticas (i.e. lipases e proteases) e compostos voláteis.
- Endophytic fungal community structure in olive orchards with high and low incidence of olive anthracnosePublication . Martins, Fátima; Mina, Diogo; Pereira, J.A.; Baptista, PaulaFungal endophytes have been increasingly recognized to promote host plant protection to pathogens, but knowledge of the multiple effects that they could have in crop diseases is still scarce. This work attempts to understand the role of fungal endophytes in crop diseases, specifically in reducing disease development and interfering on lifestyle transition of the pathogen. To accomplish this, the endophytic fungal community of reproductive organs of olive tree from two orchards showing different levels of anthracnose incidence, a major disease of olive fruits, was characterized and compared between them. The two orchards showed distinct endophytic communities, differing in species richness, abundance and composition, with highest isolation rates and richness of endophytes in the orchard with low anthracnose incidence. These differences among orchards were greater on fruits than on flowers, suggesting that these changes in endophytic fungal composition may influence the lifestyle shifts in pathogen (from latent to pathogen). A number of fungal taxa were found to be positively associated to one of the two orchards. The fungal endophytes best correlated with high incidence of anthracnose are pathogens, while endophytes-associated to low anthracnose incidence are described to protect plants. Altogether, the results suggest varying pathogen-endophyte interactions among the two orchards.
- Endophytic fungal community succession in reproductive organs of two olive tree cultivars with contrasting anthracnose susceptibilitiesPublication . Martins, Fátima; Cameirão, Cristina; Mina, Diogo; Benhadi-Marín, Jacinto; Pereira, J.A.; Baptista, PaulaThe factors shaping endophytic fungal assemblages in reproductive organs have been less evaluated than in vegetative organs. Here, the temporal dynamics of fungal endophytes in inflorescences and fruits of olive tree cultivars with contrasting anthracnose susceptibilities was assessed, starting before flowers open until fruit ripening. Fungal diversity assessed by rRNA sequencing of cultivable isolates revealed a higher richness and abundance of endophytes in inflorescences than in fruits. Endophytes from Sordariomycetes were dominant in inflorescences, while in fruits they were from Dothideomycetes. The overall assemblages of inflorescences and fruits were shaped mainly by the plant organ, followed by the phenological stage and lastly, by the plant cultivar. The importance of cultivar as a shaping factor varied according to the plant organ, being only significant in inflorescence-associated endophytes. A set of fungal taxa were positively associated with a particular cultivar and phenological stage, likely contributing to the plant anthracnose resistance.
- Epiphytic and endophytic bacteria on olive tree phyllosphere: exploring tissue and cultivar effectPublication . Mina, Diogo; Pereira, J.A.; Lino-Neto, Teresa; Baptista, PaulaVariation on bacterial communities living in the phyllosphere as epiphytes and endophytes has been attributed to plant host effects. However, there is contradictory or inconclusive evidence regarding the effect of plant genetics (below the species’ level) and of plant tissue type on phyllosphere bacterial community assembly, in particular when epiphytes and endophytes are considered simultaneously. Here, both surface and internal bacterial communities of two olive (Olea europaea) cultivars were evaluated in twigs and leaves by molecular identification of cultivable isolates, with an attempt to answer these questions. Overall, Proteobacteria, Actinobacteria and Firmicutes were the dominant phyla, being epiphytes more diverse and abundant than endophytes. Host genotype (at cultivar level) had a structuring effect on the composition of bacterial communities and, in a similar way, for both epiphytes and endophytes. Plant organ (leaf vs. twig) control of the bacterial communities was less evident when compared with plant genotype and with a greater influence on epiphytic than on endophytic community structure. Each olive genotype/plant organ was apparently selective towards specific bacterial operational taxonomic units (OTUs), which may lead to specific feedbacks on fitness of plant genotypes. Bacterial recruitment was observed to happen mainly within epiphytes than in endophytes and in leaves as comparedwith twigs. Such host specificity suggested that the benefits derived fromthe plant– bacteria interaction should be considered at genetic levels below the species.
- Evaluation of the biocontrol potential of an antagonist against olive knot disease in olive trees (Olea europaea L.)Publication . Mina, Diogo; Pereira, J.A.; Lino-Neto, Teresa; Baptista, PaulaThe olive knot, caused by the bacterium Pseudomonas savastanoi pv. savastanoi (Psv), is one of the most serious diseases affecting olive tree (Olea europaea L.) in many regions of the world and mainly in Mediterranean countries. This disease produces tumors, especially in olive tree stems and trunk, leading to the death of the plant. In recent years, the use of microbial biocontrol agents for the control of plant diseases has gained considerable attention. Previous studies have revealed that, several bacteria strains naturally occurring in the olive tree phyllosphere, exhibit capacity to inhibit in vitro growth of Psv, being the greatest antagonistic effect displayed by Bacillus En40. The aim of the present study was to evaluate the ability of this strain to suppress Psv and olive knot development in olive trees. Pot experiments were conducted with 2-year-old olive plantlets cv. Cobrançosa inoculated with the selected strain or Psv, or in combination of both. Phenotypic traits associated with plant growth (e.g. biomass yield, total shoot/root height, and photosynthetic pigments content) and biocontrol abilities (e.g. abundance of Psv and assessment of disease symptoms) were evaluated, up to 120 days after inoculation. While development and growth of Psv+antagonist-inoculated plants showed to be similar to non-inoculated plants, photosynthetic pigments contents were observed to be higher in antagonist-inoculated plants than in other treatments. When compared with Psv-inoculated plants, plants treated with the antagonist revealed a significant reduction (p<0.01) in knots formation and size. Antagonist-inoculated plants showed also a reduction of the abundance of Psv in the inoculation sites (from 22.4 to 7.5 UFC/μL, p<0.01), suggesting its capacity to reduce the patogen's growth. This strain was identified to supres Psv and disease development on olive plants and thus, it should be considered in the future as a possible biocontrol agent against olive knot disease.
- Impact of plant genotype and plant habitat in shaping bacterial pathobiome: a comparative study in olive treePublication . Mina, Diogo; Pereira, J.A.; Lino-Neto, Teresa; Baptista, PaulaPlant-inhabiting microorganisms interact directly with each other affecting disease progression. However, the role of host plant and plant habitat in shaping pathobiome composition and their implication for host susceptibility/resistance to a particular disease are currently unknown. For the elucidation of these questions, both epiphytic and endophytic bacterial communities, present in asymptomatic and symptomatic twigs from olive cultivars displaying different susceptibilities to olive knot (OK) disease, were investigated using culturing methods. OK disease was the main driver of the bacterial community, causing changes on their diversity, abundance and composition. OK disease effect was most notorious on OK-susceptible cultivar and when considering the endophytic communities. Plant habitat (epiphytes vs. endophytes) also contributed to the bacterial community assembling, in particular on symptomatic twigs (knots) of OK-susceptible cultivar. In contrast, host cultivar had little effect on the bacterial community composition, but OK-symptomatic twigs (knots) revealed to be more affected by this driver. Overall, the pathobiome seems to result from an intricate interaction between the pathogen, the resident bacteria, and the plant host. Specific bacterial genera were associated to the presence or absence of OK disease in each cultivar. Their ability to trigger and/or suppress disease should be studied in the future.
- Screening of potential biocontrol bacterial against Pseudomonas savastanoi pv. savastanoi and elucidation of their mode of actionPublication . Mina, Diogo; Pereira, J.A.; Lino-Neto, Teresa; Baptista, PaulaOver the last decades, the olive knot disease, caused by the bacterium Pseudomonas savastanoi pv. savastanoi (Psv), has been responsible for irreversible damages on olive orchards. Reduced vigor and stem dryness caused by this phytopathogen lead to a decrease in olive fruit production, conducting to countless losses for farmers. In this work, bacterial endophytes and epiphytes of olive tree phyllosphere were screened for the suppression of Psv, and several mechanisms behind this activity was also studied by evaluating indoleacetic acid (IAA), siderophore and lytic enzymes production. Interspecific interaction was assessed on solid media with agar overlays. IAA was estimated spectrophotometrically, whereas siderophores and lytic enzymes were evaluated qualitatively. Several bacterial species tested showed to reduce Psv growth up to 70%, as well as its viability. The highest inhibition was observed for Frondihabitans sp. and Paenibacillus sp. A reduction on production of both IAA and siderophore, which are associated with knot development, by Psv was noticed in the presence of the most efficient bacterial. Production of lytic enzymes by antagonists such as lipase, chitinase, protease and amylase was also identified. Altogether the results indicate that some of the bacterial tested have great potential as biocontrol agents due to their capacity to produce metabolites/lytic enzymes that can interfere with Psv growth and/or development of knots. These potential biological agents should be further evaluated under natural conditions.
- Screening the olive tree phyllosphere: search and find potential antagonists against Pseudomonas savastanoi pv. savastanoiPublication . Mina, Diogo; Pereira, J.A.; Lino-Neto, Teresa; Baptista, PaulaOlive knot (OK) is a widespread bacterial disease, caused by Pseudomonas savastanoi pv. savastanoi (Pss), which currently has not effective control methods. The use of naturally occurring microbial antagonists, such as bacteria, as biocontrol agents could be a strategy to manage this disease. The objective of this work was to select bacteria from olive tree phyllosphere able to antagonize Pss using in vitro and in planta experiments. The elucidation of their modes of action and the potential relationship between antagonism and bacteria origin has been investigated, as well. To this end, 60 bacterial isolates obtained from the surface and inner tissues of different organs (leaves, twigs, and knots), from two olive cultivars of varying susceptibilities to OK, were screened for their in vitro antagonistic effect against Pss. A total of 27 bacterial strains were able to significantly inhibit Pss growth, being this effect linked to bacteria origin. Strains from OK-susceptible cultivar and colonizing the surface of plant tissues showed the strongest antagonistic potential. The antagonistic activity was potentially due to the production of volatile compounds, siderophores and lytic enzymes. Bacillus amyloliquefaciens P41 was the most effective antagonistic strain and their capacity to control OK disease was subsequently assayed using in planta experiments. This strain significantly reduces OK disease severity (43.7%), knots weight (55.4%) and population size of Pss (26.8%), while increasing the shoot dry weight (55.0%) and root water content (39.6%) of Pss-infected olive plantlets. Bacterial isolates characterized in this study, in particular B. amyloliquefaciens P41, may be considered as promising biocontrol candidates for controlling OK disease.
- The effect of olive knot disease in bacterial communities associated to olive phyllospherePublication . Mina, Diogo; Pereira, J.A.; Lino-Neto, Teresa; Baptista, PaulaThe interactions between microorganisms sharing the same phyllosphere environment can be highly relevant for plant health. Although such interactions are ubiquitous in nature, the possible interaction between the incoming pathogen and the resident microbial flora, as well as the impact of these interactions on disease development/suppression, are unknown and not understood. To assess this, we will use in this study the olive knot disease as a model system. This disease is caused by the bacterium Pseudomonas savastanoi pv. savastanoi (Psv), that produced knots, mainly on olive tree twigs and young branches. Endophytic and epiphytic bacterial were isolated from asymptomatic twigs and knots of olive trees from two cultivars with different susceptibilities to olive knot (cv. Verdeal- Transmontana - susceptible; cv. Cobrançosa - tolerant). Bacterial isolates obtained were molecularly identified through sequencing of V1 - V4 regions from 16S rDNA. Overall, 73 species belonging to 37 genera were identified. The composition of bacterial community colonizing asymptomatic twigs changed drastically when becomes diseased. A set of bacterial was showed to be highly associated with either asymptomatic twigs or knot of each cultivar, suggesting that they might h also to be extremely different between cultivars, suggesting an effect of the cultivar in bacterial community assemblage. Future research should be carried out in order to identify it these bacterial-bacterial and bacterial-plant interactions can be really part of host defense against olive knot disease.