Evaluation of the biocontrol potential of an antagonist against olive knot disease in olive trees (Olea europaea L.)
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resumo
The 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.
