Bactericidal and plant defense elicitation activities of Eucalyptus oil decrease the severity of infections by Xylella fastidiosa on almond plants

Abstract

The activity of Eucalyptus essential oil against eleven strains pertaining to six species of plant pathogenic bacteria was studied using growth inhibition and contact assays. All strains were susceptible to the formulation EGL2, and Xylella fastidiosa subspecies and Xanthomonas fragariae were the most sensitive. The bactericidal effect was strong causing 4.5 to 6.0 log reductions in survival in 30 min at concentrations in the range of 0.75 to 15.0 μl/ml depending on the bacteria tested. Transmission electron microscopy of the formulation EGL2 against the three X. fastidiosa subspecies studied allowed the observation of a strong lytic effect on bacterial cells. In addition, the preventive spray application of EGL2 to potted pear plants subsequently inoculated with Erwinia amylovora significantly decreased the severity of infections. Almond plants treated by endotherapy or soil drenching, and then inoculated with X. fastidiosa showed a significant decrease in disease severity as well as in the levels of the pathogen, depending on the strategy used (endotherapy/soil drenching, preventive/curative). The treatment by endotherapy in almond plants induced the expression of several genes involved in plant defense. It was concluded that the reduction of infections by the Eucalyptus oil treatments was due to the combination of its bactericidal and plant defense induction activities.

Xylella fastidiosa: A Glimpse of the Portuguese Situation

“…The study found that all phytopathogenic bacteria were susceptible to the oil, with Xf and Xanthomonas fragariae being the most affected. The bactericidal effect was particularly strong, with a lytic effect observed in three subspecies of Xf used in the study [111].…”

Antibacterial effect of essential oils and their components against Xanthomonas arboricola pv. pruni revealed by microdilution and direct bioautographic assays

“…(2011) (MIC 500 µL/L). Montesinos et al. (2023) reported a reduced susceptibility of Xap (MIC 10 – 30 µl/mL) and other species such as X. fragariae and X. axonopodis pv.…”

“…The Xap isolates tested in this study (Xap3, XapG2) showed higher sensitivity (with MIC values of 125 and 250 µg/mL) to lemon grass EO than the Xap strain examined by Zhao et al (2011) (MIC 500 µL/L). Montesinos et al (2023) reported a reduced susceptibility of Xap (MIC 10 -30 µl/mL) and other species such as X. fragariae and X. axonopodis pv. vesicatoria (MIC < 5 and 10 -30 µl/mL, respectively) to eucalyptus EO, as compared to our observations, however they used a different method, the agar HPTLC chromatograms with retardation factor (hR F ) scale of thyme (T), cinnamon (CN), clove (CL), tea tree (TT), rosemary (R), eucalyptus (EU), lemon grass (LG), lemon balm (LB1 from Primavera, LB2 from Olivia Naturals), and citronella grass (CG) essential oils, and thymol (t), transcinnamaldehyde (c), eugenol (e), citral (ci: neral+geranial), and citronellal (cl) standards after derivatization with vanillin-sulphuric acid reagent (A, D, G), and bioautograms using Xanthomonas arboricola pv.…”

“…The great potential of EOs as biopesticides is based on their herbicidal ( Li et al., 2020 ; Yasar et al., 2021 ), insecticidal ( Isman et al., 2011 ; Ebadollahi et al., 2022 ), acaricidal ( Camilo et al., 2017 ; Nwanade et al., 2021 ), nematicidal ( Avato et al., 2017 ; Catani et al., 2023 ), and antimicrobial effects ( Božik et al., 2017 ; Assadpour et al., 2023 ), and has been well demonstrated by usage of commercialized bioinsecticides ( Isman, 2020 ). A variety of EOs has shown effectiveness against several Xanthomonas species ( Horváth et al., 2004 ; Huang and Lakshman, 2010 ; Bajpai et al., 2011 ; Lucas et al., 2012 ; Móricz et al., 2015a ; Móricz et al., 2015b ; Gormez et al., 2016 ; Mirzaei-Najafgholi et al., 2017 ; Singh et al., 2017 ; Kumar et al., 2021 ; Hakalová et al., 2022 ; Montesinos et al., 2023 ) and especially against Xap ( Biavati et al., 2004 ; Mahmoudi et al., 2010 ; Zhao et al., 2011 ; Montesinos et al., 2023 ).…”