[en] The extensive use of synthetic pesticides leads to risks for both human health and
ecosystems due to the non-target toxicity and stability they present. Natural mole cules are investigated to achieve more sustainable production methods and meet so cietal/consumer’s expectations. The present thesis focuses on apple production and
control of its most detrimental pests in orchards the Rosy Apple Aphid (RAA), Dys aphis plantaginea Passerini, using essential oils (EOs). This work was realised as part
of a larger project (Tree-Injection) whose aim was to use EOs as a botanical insecti cide combined with trunk injection. This project presents an innovative and original
approach to implementing practical application of biopesticide.
Due to their large spectra of biological activities EOs have been actively investi gated as an alternative to numerous synthetic biocide products. However, apart from
herbicidal applications their phytotoxic properties are a major drawback to their ap plicability as biopesticides for sustainable agriculture. The first part of the present
thesis synthesises the cellular and functional impacts of EOs leading to phytotoxicity.
Physiological disturbances and their putative molecular targets are described. New
opportunities regarding the development of biopesticides are discussed, including bi ostimulation and defence elicitation properties occurring below the phytotoxicity
threshold.
The phytotoxic properties of Cinnamomum cassia EO (CEO) on apple tree (Malus
x domestica Borkh) was studied in terms of oxidative burst (glutathione redox state)
and oxidative damage on lipids (malondialdehyde). A rapid/strong oxidative burst
occurred at high CEO concentrations, decreasing the reduced glutathione content in
in the leaves. This burst is followed by apparition of oxidative damage, as suggested
by an increase in malondialdehyde. Furthermore, at lower concentrations, induction
of systemic defence was investigated by following the gene expression level of spe cific defence pathways (PR proteins, secondary metabolism, oxidative stress, parietal
modifications). Hence, these findings help to draft innovative pest management strat egies that consider both the risks (phytotoxicity) and benefits (defence activation
combined with direct biocide properties) of biopesticides based on EOs.
Due to EO rapid degradation in the environment and their volatility, the potential
to use alternative methods of application, such as trunk injection was explored in this
thesis. Systemic translocation of EOs through the xylem following the injection of
Cinnamomum cassia and Mentha spicata nanoemulsions in plant’s vascular system
was demonstrated by targeted volatile organic compounds (VOCs) analyses. Given
systemic translocation, increased production and release of biogenic VOCs, and ab sence of phytotoxicity, this work can be seen as proof of concept for the use of EOs
with trunk injection.
4
Finally, laboratory and field trials assayed the potential to control RAA based on
CEO trunk injection. Laboratory trials demonstrated promising results and were
scaled up during two-year field trials on trees of the ‘Jonagold’ cultivar. Considering
the pest life cycle, injections were applied as curative (during the vegetative stage)
and preventive treatments (at budburst). RAA population dynamics (number of col onies and aphids) were tracked in addition to other predator and pest populations.
Given their importance, tree physiology and the emission of VOCs were followed.
Total and commercial apple yield were estimated, in addition to the absence of trans cinnamaldehyde residue (main compound in EO) in fruit. The final part of this thesis
investigates the practical feasibility of laboratory-effective solutions in agronomic
conditions and identifies challenges and limitations that need to be addressed.
Globally, this thesis furthers the potential of biopesticides based on EOs in fruit
arboriculture and highlights a fruitful research perspective for pest control compatible
with integrated pest management (IPM).
