ROLE OF OLIVE TREE PHYLLOSPHERE MICROORGANISMS IN THE BIOLOGICAL CONTROL OF OLIVE LEAF SPOT AND OLIVE KNOT

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Endophytic and epiphytic fungal community associated to olive tree differ in antagonistic activity against Pseudomonas savastanoi pv. savastanoi

Publication . Gomes, Teresa; Pereira, J.A.; Lino-Neto, Teresa; Baptista, Paula

The Olive knot (OK) caused by the Pseudomonas savastanoi pv. savastanoi (Psv) is an important disease, causing severe damages and yield losses in olive trees worldwide (Olea europaea L.). In a previous study we have isolated this bacterium from the phyllosphere of olive tree, together with many fungal species. In these complex communities, microorganisms compete with each other for space and resources, promoting survival of the best-adapted individuals. This has prompted interest in the exploitation of these microorganisms for OK control. In this study, 48 fungal species from the endo- and epiphytic communities of olive twigs were screened for the growth inhibition of the phytopathogen Psv under in vitro conditions. The time course of interspecific interactions (24, 48, 72 and 144h) was studied in potato dextrose agar and olive leaf + twig extract (OLTE), by assessing a clear zone of growth inhibition around fungal colony. Results showed that epiphytic community was the main reservoirs for antagonistic fungi. Almost 75% of the tested epiphytes inhibited Psv growth, being Dothiorella iberica, Aspergillus felis and Aspergillus brasiliensis the most prominent species. The proportion of antagonists within endophytic community was lower (11%), being the most efficient Epicoccum nigrum and Rhinocladiella similis. The antibacterial activity was observed to be significantly (p<0.01) affected by growth medium and time of interaction. Higher growth inhibition was found in the OLTE culture media, showing that inhibition of these endophytic and epiphytic fungi was specifically enhanced by the host plant extract. Most of the fungi tested (up to 64%) from both microenvironment showed higher antibacterial activity in the first 24 hours of interaction, whereas only 16% and 19% strongly inhibited Psv after 48 and 144 hours of interaction, respectively. Altogether, the results indicate that D. iberica, E. nigrum and A. felis, are the best candidates for the biocontrol of olive knot. These potential biological agents should be considered and further evaluated under natural conditions

2017Conference object

Open access

Endo- and epiphytic fungal communities of olive twigs is influenced by cultivar and olive knot infection

Publication . Gomes, Teresa; Pereira, J.A.; Lino-Neto, Teresa; Bennett, Alison E.; Baptista, Paula

Olive tree phyllosphere is colonized by a diverse microbial assemblage that may interact with pathogenic fungi, making them potential candidates for disease supression. Olive knot (OK) is a disease caused by the bacterium Pseudomonas savastanoi pv. savastanoi (Psv.) with significant economic losses in olive tree (Olea europaea L.). With this work we want to evaluate the effect of cultivar and OK infection on both endo- and epiphytic fungal community inhabiting olive twig tissues. For this, fungal composition and diversity was assessed in both asymptomatic and OK-symptomatic twigs of tree co-occurring olive cultivars with different susceptibilities to OK disease. The identification of isolated species was performed by ITS rDNA sequencing. The cultivar and OK infection were important in shaping both endophytic and epiphytic fungal communities. Fungal community composition was found to differ significantly (p=0.005) between olive tree cultivars, being Nectriaceae the dominant family in cvs. Cobrançosa and Verdeal Transmontana, whereas Pleosporaceae was dominant in the cv. Madural. Epiphytic and endophytic fungal communities also differed in size and in composition in asymptomatic and OK-symptomatic twigs, for the three cultivars. In general, asymptomatic twigs were more diverse and rich (up to 1.4-fold) when compared to OK-symptomatic twigs. Among the species identified in the asymptomatic tissues, Cladosporium cladosporioides and Chromelosporium carneum were the most frequently isolated within epiphytic and endophytic community, respectively; whereas in the OK-symptomatic tissues Cladosporium sp. and Fusarium lateritium were the most frequently isolated within epiphytic and endophytic community, respectively. According to indicator species analysis C. carneum, Pyronema dosmesticum and Phoma aloes (IndVal up to 0.56) may be promising species in the OK suppression. Better acknowledgement should be developed in order to uncover their role on plant health.

2017Conference object

Open access

Bacterial disease induced changes in fungal communities of olive tree twigs depend on host genotype

Publication . Gomes, Teresa; Pereira, J.A.; Lino-Neto, Teresa; Bennett, Alison E.; Baptista, Paula

In nature, pathogens live and interact with other microorganisms on plant tissues. Yet, the research area exploring interactions between bacteria-fungi and microbiota-plants, within the context of a pathobiome, is still scarce. In this study, the impact of olive knot (OK) disease caused by the bacteria Pseudomonas savastanoi pv. savastanoi (Psv) on the epiphytic and endophytic fungal communities of olive tree twigs from three different cultivars, was investigated in field conditions. The ITS-DNA sequencing of cultivable fungi, showed that OK disease disturbs the resident fungal communities, which may reflect changes in the habitat caused by Psv. In particular, a reduction on epiphyte abundance and diversity, and changes on their composition were observed. Compared to epiphytes, endophytes were less sensitive to OK, but their abundance, in particular of potential pathogens, was increased in plants with OK disease. Host genotype, at cultivar level, contributed to plant fungal assembly particularly upon disease establishment. Therefore, besides fungi - Psv interactions, the combination of cultivar - Psv also appeared to be critical for the composition of fungal communities in olive knots. Specific fungal OTUs were associated to the presence and absence of disease, and their role in the promotion or suppression of OK disease should be studied in the future.

2019Journal article

Open access

Endophytic and Epiphytic Phyllosphere Fungal Communities Are Shaped by Different Environmental Factors in a Mediterranean Ecosystem

Publication . Gomes, Teresa; Pereira, J.A.; Benhadi-Marín, Jacinto; Lino-Neto, Teresa; Baptista, Paula

The diversity and factors influencing fungal assemblages in phyllosphere of Mediterranean tree species have been barely studied, especially when endophytic and epiphytic communities are simultaneously considered. In this work, the endophytic and epiphytic fungal communities from olive tree phyllosphere were studied.This tree species is natural from the Mediterranean region and adapted to grow under adverse climatic conditions. The main objectives were to determine whether there are differences between both fungal communities and to examine whether different abiotic(climate-related) and biotic(plantorgans)factors play a pivotal role in structuring these communities. Both communities differed in size and composition, with epiphytic community being richer and more abundant, displaying also a dominance of melanized fungi. Season was the major driver of community composition, especially of epiphytes. Other drivers shaping epiphytes were wind speed and temperature, while plant organ, rainfall, and temperature were the major drivers for endophytic composition. In contrast, canopy orientation caused slight variations in community composition of fungi, but with distinct effects in spring and autumn seasons. In conclusion, epiphytic and endophytic communities are not driven by the same factors. Several sources of variation undergo complex interactions to form and maintain phyllosphere fungal community in Mediterranean climates. Climatic parameters have influence on these fungal communities, suggesting that they are likely to be affected by climate changes in a near future.

2018Journal article

Open access