Globalization propelled human migration and commercial exchanges at the global level, but woefully led to the introduction of non-indigenous organisms into several agroecological systems. These include pathogenic bacteria with devastating consequences for numerous crops of agronomical importance for food production worldwide. In the last decade, research efforts have focused on these noxious organisms, aiming to understand their evolutionary processes, degree of pathogenicity, and mitigation strategies, which have allowed stakeholders and policymakers to develop evidence-based regulatory norms to improve management practices and minimize production losses. One of these cases is the bacterium Pseudomonas syringae pv. actinidiae (Psa), the causal agent of the kiwifruit bacterial canker, which has been causing drastic production losses and added costs related to orchard management in the kiwifruit industry. Although Psa is presently considered a pandemic pathogen and far from being eradicated, the implementation of strict regulatory norms and the efforts employed by the scientific community allowed the mitigation, to some extent, of its negative impacts through an integrated pest management approach. This included implementing directive guidelines, modifying cultural practices, and searching for sources of plant resistance. However, bacterial pathogens often have high spatial and temporal variability, with new strains constantly arising through mutation, recombination, and gene flow, posing constant pressure to agroecosystems. This review aims to critically appraise the efforts developed to mitigate bacterial pathogens of agronomical impact, from orchard management to genome analysis, using Psa as a case study, which could allow a prompter response against emerging pathogens in agroecosystems worldwide.

This paper proposes a mathematical model based on a mechanistic approach and previous research findings for the bacterial canker disease development in kiwifruit vines. This disease is a leading cause of severe damage to kiwifruit vines, particularly in humid regions, and contributes to significant economic challenges for growers in many countries. The proposed model contains three parts. The first one is the model of the kiwifruit vine describing its light interception, its carbon acquisition, and the partitioning dynamics. The carbon resource represents the chemical energy required for maintaining the necessary respiration of the living organs and their growth processes. The second part of the model is the dynamics of the pathogenic bacterial population living within the vine’s tissues and competing with them for the carbon resource required for their proliferation. The third part of the model is the carbon dynamics described by a mass conservation formula which computes the remaining amount of carbon available for competition. The model was validated by comparing simulations with experimental results obtained from growth chambers. The results show that the proposed model can simulate reasonably well the functional part of the vine in both the healthy case and the disease case without plant defense mechanisms in which the bacteria are always dominant under favorable environmental conditions. They also show that the environmental effects on the vine’s growth and the infection progress are taken into account and align with the previous studies. The model can be used to simulate the infection process, predict its outcomes, test disease management techniques, and support experimental analyses.

Plant essential oils (EOs) are attracting interest as ecofriendly alternatives to antibiotics and copper-based control of kiwifruit bacterial canker (KBC), caused by Pseudomonas syringae pv. actinidiae (Psa). This study chemically profiled six EOs (anise, basil, cardamom, cumin, fennel, and laurel) and evaluated their antimicrobial activity both in vitro and in planta. The in vitro assay targeted four strains, two of Psa and two of the low-virulent P. syringae pv. actinidifoliorum (Pfm), whereas the in planta assay focused on the highly virulent Psa7286 strain, assessed under preventive and curative application regimes (i.e., 14 days pre- or post-inoculation, respectively). Cumin, with cuminaldehyde as its major component (48%), was the most effective EO in vitro, significantly inhibiting growth at 5–10% concentration, whereas anise, rich in anethole (89%), was consistently the least effective one. However, the in planta application of the EOs produced antimicrobial effects that differed markedly from in vitro results and showed strong dependence on the timing of application. Preventive treatment significantly reduced Psa endophytic populations in basil (70%), anise (54%), laurel (42%), and cumin (35%) compared to untreated plants. In contrast, when the EOs were applied post-inoculation (curative treatment), a significant decrease in Psa colonization was observed in laurel (81%), cardamon (70%), cumin (31%) and fennel (29%). Although plant EOs are gaining momentum in the control of Psa and other diseases, translation from in vitro to in planta efficacy is not direct and is strongly timing-dependent, which underscores the need to perform validation trials in planta and to fine-tune application schedules for the integrated management of KBC.

Pseudomonas syringae pv. actinidiae (Psa) is the most destructive pathogen of kiwifruit, and the absence of curative measures makes the management of Psa-induced kiwifruit bacterial canker (KBC) particularly challenging. Elettaria cardamomum produces an essential oil (CAR) rich in bioactive compounds with demonstrated potential to act directly against Psa, but its mechanisms of action remain insufficiently explored. Here, we investigated CAR’s mode of action in plants with established mild KBC symptoms, and assessed its potential as a plant elicitor. In the in planta assay, CAR application (0.1% w/v, applied 7 days after inoculation) reduced KBC symptoms, with the strongest effect observed 14 days after treatment (DAT). However, CAR did not significantly affect oxidative stress biomarkers, antioxidant system, pigments and primary metabolism, or the expression of target genes related to systemic acquired resistance or salicylic acid and jasmonic acid pathways. For instance, Psa inoculation significantly upregulated PR1 (≈5.4-fold) and PR5 (≈4.3–5.5-fold), irrespective of CAR application. Complementary in vitro assays revealed a transient, phase-dependent antimicrobial activity of CAR: although the effect disappeared by 32 h in liquid-phase assay and no inhibition was observed under vapor-phase exposure, a strong reduction in Psa viable cells (79.7%) was observed after 8 h exposure in the liquid phase. This study demonstrates that CAR exerts a direct, albeit transient, antibacterial effect against Psa, conferring curative activity when applied to plants with mild KBC symptoms. Consequently, repeated applications may be required to maintain disease suppression, as CAR does not appear to induce a sustained preventive defense response in the host.