Endo- and epiphytic bacteria from olive tree phyllosphere with biocontrol abilities against olive knot

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The effect of olive knot disease in bacterial communities associated to olive phyllosphere

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

The 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.

2018Conference object

Open access

Screening of potential biocontrol bacterial against Pseudomonas savastanoi pv. savastanoi and elucidation of their mode of action

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

Over 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.

2017Conference object

Open access

Biological control of Pseudomonas savastanoi pv. savastanoi by two bacterial isolated from olive tree phyllosphere

Publication . Diogo, Mina; Santos, Alba; Pereira, J.A.; Lino-Neto, Teresa; Baptista, Paula

Olive knot disease, caused by the bacterium Pseudomonas savastanoi pv. savastanoi (Psv), has been responsible for high economical crop losses in olive orchards, especially in Mediterranean countries. Olive knot cannot be eradicated once it is established in an orchard, and therefore its control is based on preventive measures. Laboratory experiments previously performed by us have showed the capacity of some bacterial species, isolated from olive tree phyllosphere, to inhibited Psv growth. In the present work, the two most promising bacterial isolates (i.e. Frondihabitans sp. and Paenibacillus sp.) were evaluated for the control of Psv in olive plantlets (Olea europaea L.) under greenhouse conditions, to predict their effect in a more natural condition. In pot experiments, two-year-old olive plants cv. Cobrançosa were inoculated with the antagonistic bacteria and Psv individually or in combination. Inoculations were performed in wounds previously made in three different sites of the main stem. Thirty replicate plants were used per strain. The plants were observed for symptom development and the number of bacteria on the inoculation sites was periodically evaluated, for up to 120 days after inoculation. To quantify the reduction of symptom expression, knots were excised from stems and their weights were compared between treatments. Inoculation with Psv resulted in the formation of knots with significantly higher weight values compared to plants inoculated simultaneously with Psv and antagonistic bacteria. Both tested bacterial also showed the capacity to reduce the amount of Psv in the inoculation sites, suggesting their effectiveness in controlling the multiplication of the pathogen. Data presented here demonstrate for the first time the potential of these bacteria for suppression of olive knot, and these two species should be considered in the future as potential biocontrol agents against Psv.

2017Conference object

Open access