Temporal proteomic analysis reveals a three-phase adaptation strategy in Phytophthora cinnamomi during salinity stress.

Subtilisin-like proteases (SBTs) are a large family of serine peptidases involved in diverse biological processses, including plant stress responses, but remain poorly characterized in forest trees. In this study, we report the genome-wide identification and characterization of the SBT gene family in Quercus ilex (QiSBT), with a focus on their transcriptional organization and response to Phytophthora cinnamomi infection. A total of 87 QiSBT genes were identified, structurally annotated, and phylogenetically classified into seven subfamilies based on comparative analyses with Arabidopsis thaliana, Populus trichocarpa, and three other Quercus species (Q. lobata, Q. robur, and Q. variabilis). Analyses of conserved domains and gene structures revealed a high degree evolutionary conservation, with one subfamily enriched in intronless or intron-poor genes. Promoter analysis identified numerous stress- and hormone-responsive cis-elements, suggesting potential transcriptional regulation under environmental stress conditions. Expression profiling under P. cinnamomi infection revealed differential transcriptional responses within the QiSBT gene family. In particular, QiSBT24, QiSBT63, and QiSBT69 showed significant induction in inoculated seedlings, with approximate 3-, 8-, and 30-fold, respectively. These results provide new insights into the structure, evolution, and potential defense-related roles of SBTs in Q. ilex, offering a foundation for future functional aimed at understanding their contribution to resistance mechanisms in Mediterranean oak species.

Pulsed electric field (PEF) technology is a non-chemical approach with potential to control soilborne agricultural pests. PEF disrupts cellular membranes through short, high-energy electrical pulses. Treatment efficacy depends on electric field strength, pulse frequency, and applicator design. Field strength reflects the intensity of the electric field driving electroporation, whereas energy density represents the cumulative dose delivered to the system, and pulse frequency determines how that dose is distributed over time. In this study, two soil-applied PEF applicators, vertical pins (VP) and parallel plates (PP), were evaluated for suppression of weeds, plant-parasitic nematodes, and soilborne pathogens. Numerical simulations showed that the PP configuration generated a more uniform electric field distribution than the VP design. Consistent with these predictions, the PP applicator provided greater biological suppression across target organisms. Cyperus esculentus biomass declined progressively with increasing energy density and was significantly reduced at ≥100 J cm-3. The PP applicator also reduced Meloidogyne chitwoodi second-stage juveniles by up to 100% at 25 J cm-3 and pulse frequencies above 60 Hz. Densities of Pratylenchus neglectus and M. chitwoodi were reduced by more than 98% at 400 V mm-1. Weed responses were species dependent: biomass of C. esculentus and Digitaria sanguinalis declined at 100-200 J cm-3, whereas Echinochloa crus-galli required higher energy inputs for control. Soilborne pathogens also differed in susceptibility, with Phytophthora cinnamomi and P. plurivora reduced by 94% at moderate field strengths (100-200 V mm-1), while Verticillium dahliae was suppressed by up to 97% at 200-400 V mm-1 and 80 Hz. Overall, nematodes and soilborne pathogens were suppressed at substantially lower energy densities (~25 J cm-3) than weed propagules, which generally required ≥100-200 J cm-3 for effective biomass suppression. These results demonstrate that PEF can effectively suppress multiple soilborne pests. Additionally, the results highlight the importance of applicator design and electrical parameters in determining treatment efficacy, supporting the potential of PEF as a scalable and sustainable soil disinfestation technology.

Portugal has over one-third of the Quercus suber L.world area, a natural treasure threatened by a progressive decline, which has been witnessed during the last decades by increasing tree mortality, where Phytophthora cinnamomi Rands is considered the main cause. Biochar has proven to be a product of great interest for application in agriculture due to its benefits in terms of soil chemical and physical properties. There is also evidence of phytosanitary status improvement, including P. cinnamomi, namely inducing resistance in plants. Three biochars of different origins were tested under lab and greenhouse conditions: one prepared from Acacia spp., another from a mixture of woody plant species, and a third from macroalgae Oedogonium intermediumWittr. The aim was to evaluate the biochars effect on root rot disease caused by P. cinnamomi infection testing their ability to inhibit P. cinnamomi mycelium and reproductive structures and on young Q. suber plants. Generalized linear mixed models (GLMMs) identified dose-dependent biochar responses, with Acacia at 1% and wood_mix at 5% (w/w) emerging as optimal concentrations. These treatments markedly suppressed P. cinnamomi reproductive structures (p < 0.001), promoted cork oak plant growth (root recovery 79-80% above pathogen-challenged controls), and maintained favorable soil chemical parameters, representing a compelling integration of pathogen suppression with plant health benefit. The possibility that biochar may act as a duplibiotic in relation to soil microbiota is discussed. Our observations allow us to conclude that biochar could be an option to include in an integrated strategy plan to control the root rot disease in cork oak caused by P. cinnamomi.

Avocado orchards in southern India experience annual yield losses of 20–40% due to foliar pathogens, including Anthracnose (Colletotrichum Gloeosporioides), Root Rot (Phytophthora Cinnamomi), Algal Leaf Spot (Cephaleuros Virescens) and Scab (Elsinoe Perseae). Conventional field scouting and RGB based imaging are unable to detect early-stage infections beneath dense canopy cover, delaying timely intervention and contributing to excessive fungicide use. To address these limitations, this study introduces a UAV based multispectral-RGB imaging pipeline paired with a deep learning detection framework built from the YOLO family of models (YOLOv5s-YOLOv10s) evaluated on a field-collected dataset of 5,953 annotated images comprising 35,422 bounding box instances across four foliar disease classes. A Sequential SGD-AdamW (SeqOpt) optimizer was designed to stabilize gradient dynamics multispectral noise by combining the global exploration capability of SGD in early training phases with the adaptive refinement precision of AdamW in later phases. As a result, SeqOpt achieved an 8% reduction in final loss and a 14% improvement in stability index compared to individual baseline optimisers, confirming superior convergence quality under spectrally heterogeneous training conditions. Systematic benchmarking across all six architectures demonstrated that YOLOv10s-SeqOpt delivered the highest detection performance, achieving 96.0% accuracy, F1-score = 0.911, and mAP@0.5 = 0.937 on multispectral validation set. YOLOv10s-SeqOpt consistently outperformed YOLOv5s-YOLOv9s across both RGB and multispectral datasets, with multispectral OCN input providing measurable detection advantages over RGB across five of six architectures evaluated The optimized model was quantized and deployed on two embedded AI platforms - NVIDIA Jetson Orin Nano, achieving real-time inference at 69.5ms per frame under PyTorch runtime, and the Raspberry Pi 5, supporting scheduled survey inference at 1.545s per frame via ONNX runtime - both without thermal throttling across extended evaluation sessions. The proposed framework demonstrates field-ready capability for large-scale orchard monitoring, bridging the gap between research-grade detection models and real-world precision agriculture deployment through a validated, scalable pipeline integrating multispectral imaging, deep learning and embedded edge computing for sustainable disease management in Indian horticulture.

Understanding how plant pathogens modulate the rhizosphere microbiota is essential to integrated disease management. Here, the compositional and functional shifts in the avocado rhizosphere bacteriome induced by Phytophthora cinnamomi were assessed to identify bacterial taxa enriched in the symptomatic condition and elucidate the microbial functions modulated by the infection. Metabarcoding and metatranscriptomics analyses revealed that Phytophthora root rot (PRR) induced compositional shifts in bacterial communities, leading to the enrichment of members of MND1, RB41, and Nitrospira. Functional analysis showed that this enrichment might be due to the release of nutrients following root rot, as carbohydrate metabolism was stimulated in rhizobacterial communities of infected trees. Moreover, the relative abundance of transcripts from genes associated with stress response and cell signaling increased in some of the most active genera in the rhizosphere of PRR-symptomatic trees, suggesting their potential to mitigate the adverse effects of infection. These findings highlight the need to combine compositional and functional microbiome data to differentiate between taxa attracted by nutrient release and those contributing to the plant defense. The interactions of beneficial bacterial taxa with the pathogen should be further studied, as they may constitute promising biocontrol agents.

Targeted editing of the Cspmr4 gene via CRISPR/Cas9 to enhance tolerance to Phytophthora cinnamomi in Castanea sativa

Abstract Climate aridification and the increasing incidence of exotic pests and pathogens are contributing to a concerning global rise in tree decline and mortality. The analysis of tree elemental composition (the elementome) offers a promising tool to detect physiological disruptions and identify early‐warning signals of decline. However, the role of elemental alterations—particularly in response to exotic pathogens—remains underexplored. Here we analysed the elemental signature of tree decline in Mediterranean savanna‐type ecosystems (dehesas) invaded by the aggressive exotic soil‐borne pathogen Phytophthora cinnamomi . Using a multi‐scale approach (regional and local), we assessed root elemental concentrations and stoichiometry in relation to crown defoliation, soil physicochemical properties and P. cinnamomi abundance in 500 adult Quercus rotundifolia trees across 30 sites in Southern Spain. Our results revealed a distinct chemical signature of tree decline in the root elementome, with patterns varying across spatial scales. At the regional scale, only sodium (Na) emerged as an indicator of site‐level decline. In contrast, the local scale revealed strong and consistent chemical alterations in symptomatic trees, including elevated calcium (Ca) concentrations and reduced levels of key nutrients (potassium [K], phosphorus [P], iron [Fe], zinc [Zn]) and elemental ratios (K:Ca) compared to asymptomatic neighbours. Among all variables, the K:Ca ratio was the best discriminator between asymptomatic and symptomatic trees, showing significant associations with crown defoliation and P. cinnamomi abundance. Elevated Ca uptake in symptomatic trees may reflect a defensive response to pathogen infection but also contribute to nutritional imbalances that exacerbate decline. Synthesis . Our findings highlight the value of multi‐scale elementome analysis for identifying sites and trees vulnerable to decline. Specifically, we showed that nutritional imbalances (particularly the K:Ca ratio) can act as reliable early‐warning signals of pathogen‐driven decline in Mediterranean systems, enabling rapid management responses. We advocate further research on plant elementomes across diverse pathosystems to uncover broader patterns that could inform biosecurity programs aimed at mitigating the growing impacts of exotic pathogens worldwide.

Ceylon cinnamon (Cinnamomum verum J. Presl) bark essential oil (CBO) represents a promising source of natural bioactive compounds for biological plant protection. For the first time, the antibacterial and antifungal activity of CBO was systematically evaluated against a curated panel of phytopathogenic strains (IOR collection), revealing broad-spectrum efficacy across both bacteria and filamentous pathogens. This study evaluated its chemical composition, antimicrobial activity against phytopathogens, effects on bacterial metabolic activity, and its ability to induce plant defence responses. CBO was dominated by cinnamaldehyde, linalool, and eucalyptol. The oil exhibited strong antibacterial activity against Dickeya dadantii, Pectobacterium carotovorum, Pseudomonas syringae, and Xanthomonas hortorum as well as antifungal activity against Fusarium graminearum, F. culmorum, Rhizoctonia solani and Phytophthora cinnamomi. Metabolic assays revealed a marked reduction in bacterial metabolic activity, indicating that CBO disrupts physiological processes and inhibits growth. In planta experiments showed that foliar application of CBO stimulated PAL activity in wheat leaves without visible phytotoxic symptoms. These findings demonstrate a multifunctional mode of action of CBO, combining direct antimicrobial effects with the elicitation of plant defence responses, and support its potential application in sustainable crop protection.

Phytophthora root rot (PRR), caused by Phytophthora cinnamomi, is a major production challenge for avocado growers worldwide. PRR management includes cultural practices, the use of resistant rootstocks, and fungicide applications, however, the recent emergence of more virulent and potassium phosphite-resistant pathogen populations has reduced the effectiveness of these management practices. We evaluated the efficacy of Oomycota fungicides to control PRR in five unreleased experimental rootstocks developed by the University of California, Riverside (UCR) and two commercial rootstocks grafted with 'Hass' under greenhouse conditions. All rootstocks were inoculated with P. cinnamomi and treated with either one of six fungicides representing different modes of action to assess PRR management by evaluating PRR incidence, pathogen propagules in soil (ppg), root health, and stem water potential (SWP). All fungicides reduced PRR incidence and pathogen ppg values ranging from 2.1 to 12.3 % and 0.8 to 2.7 ppg, respectively, compared with the untreated control values (36.2% and 11.8 ppg). Potassium phosphite treatments were only effective when using the most resistant rootstocks. Oxathiapiprolin was the best treatment followed by mefenoxam, fluopicolide, ethaboxam, and mandipropamid. The five UCR experimental rootstocks exhibited significantly less PRR incidence (1.8 to 7.4 %) and P. cinnamomi ppg (0.7 to 2.5 ppg) than the susceptible control (28.2% and 8.9 ppg). Improved PRR management was achieved by combining the most resistant rootstock with fungicide treatments, indicating the cumulative effect of rootstock resistance and fungicide treatment. These results support the commercial release of these UCR experimental rootstocks and registration of new Oomycota fungicides to control avocado PRR.

Mediterranean agroforestry systems (AFSs), typified by the Iberian Dehesas and Portuguese Montados, are multifunctional landscapes where Quercus species act as ecological keystones sustaining biodiversity, soil fertility, and rural livelihoods. These systems are increasingly affected by complex oak decline syndromes driven by drought, soil degradation, and climate-induced pathogen outbreaks. Conventional chemical controls are often ineffective and environmentally detrimental, underscoring the need for ecologically sound management alternatives. This review synthesizes recent advances in the application of microbial biological control agents (MBCAs) to manage diseases in Mediterranean Quercus species, including Q. ilex, Q. suber, Q. faginea, and Q. pyrenaica. We conducted a structured literature review using predefined keyword searches in Web of Science and Scopus, followed by the screening of records to identify 22 relevant peer-reviewed studies on microbial disease control in Mediterranean Quercus species. We identified 20 peer-reviewed studies that reported that MBCAs—primarily from Bacillus, Serratia, Streptomyces, Trichoderma, Simplicillium and Alternaria—exert biocontrol effects through antibiosis, mycoparasitism, competition for ecological niches, and the induction of host defense responses. Although most experiments were conducted in vitro, some demonstrated significant disease suppression in seedlings infected by Phytophthora cinnamomi, Diplodia corticola, and Biscogniauxia mediterranea. Future research should integrate field-based validation and microbiome-oriented forest management approaches to enable the operational use of microbial-based disease control strategies in AFS landscapes.

Species of the genus Phytophthora are among the most detrimental plant pathogens globally, representing a significant threat to global agriculture, horticulture, and forestry. These zoosporic oomycetes have historically caused devastating outbreaks, including, just to mention a few, late blight of potato in Ireland; jarrah dieback of eucalyptus in Western Australia; ink disease of chestnut in Europe; sudden oak death and sudden larch death of coast live oak and tanoak in the Western US, and of Japanese larch in the UK. The environmental and ecological impacts of the diseases they cause result in significant economic costs that often have social repercussions. With the acceleration of globalization, enhancing the movement of plant material, in particular with the global live plant trade, the spread of Phytophthora to new, uncontaminated territories has intensified. Nurseries play a key role in the movement of these pathogens, the trade of contaminated stocks representing their major dissemination route. However valuable, conventional detection techniques, including baiting and direct isolation, are too slow and labour-intensive to meet current diagnostic requirements, particularly given the huge volumes of plants traded globally. This problem becomes even more acute when large volumes of potentially infectious plant material need to be processed in a short time frame, as it is often necessary to provide accurate and timely responses to interested parties. Early and precise detection is thus vital to avert outbreaks and mitigate long-term consequences. This review evaluates and contrasts the efficacy of novel detection methods against traditional approaches, emphasizing their significance in managing the escalating threat posed by Phytophthora spp. worldwide. Despite technological advances, critical challenges remain that limit the reliability and large-scale adoption of new diagnostic methods. Research still needs to bridge the gap between the laboratory and the field in terms of accuracy, sensitivity and diagnostic costs. Recent innovations focus on sensor technology and point-of-care (POC) devices for faster, more sensitive, and low-cost specific detection of Phytophthora spp. in plant matrices, water and soil. Enhancing diagnostic capabilities through these tools is crucial for protecting agricultural productivity, local economies, and natural ecosystems.

To determine the diversity of oomycetes in Vietnam, particularly in the presumed center of origin of most Phytophthora taxa, isolates were collected from rivers, agricultural soils, and forested areas. Species identification was performed using sequences from the internal transcribed spacer (ITS) and cytochrome 2 oxidase (cox2) regions of the genome. Of the 245 isolates included in this study, the majority (66.5%) were identified as Phytopythium spp., followed by Phytophthora spp. (31%) and Pythium spp. (2.4%). The most prevalent species were Phytopythium vexans and Phytophthora cinnamomi, accounting for 51.8 and 24.5%, respectively, of all isolates obtained. A total of 17 isolates were identified as belonging to multiple undescribed species. From agricultural soils, only one isolate each of Phytophthora and Pythium was obtained, with the remaining 93% belonging to the genus Phytopythium. This study shows that natural and agricultural areas in Vietnam harbor a wide diversity of oomycetes, including several undescribed species. The identification of oomycete species in a center of origin will help identify potential emerging pathogens that can become a threat to U.S. agriculture.

Floral nectar-living microbes contribute to flower protection and pollinator health and are primarily determined by nectar chemical composition. Microbial communities in non-hexose-rich nectars and their ability to inhibit pathogens and modulate plant development have been poorly explored. We used metabarcoding to examine the richness and relative abundance of bacteria and fungi from avocado, a globally important crop with a unique nectar chemical composition, whose production is severely affected by diseases and low pollination rates. We also explored the antagonistic activity of the nectar microbial culturable fraction and its volatile organic compounds (VOCs) against avocado pathogens Phytophthora cinnamomi and Colletotrichum gloeosporioides, and against the most devastating honeybee pathogens Ascosphaera apis and Paenibacillus larvae. Furthermore, we experimentally analyzed the effects of microbial isolates and their VOCs on plant growth and the activation of jasmonic acid (JA) defense responses in Arabidopsis thaliana. Pseudomonas, Acinetobacter, Protomyces, and Vishniacozyma were the dominant microbial genera inhabiting avocado nectar. From 43 evaluated isolates, 17 bacteria and three yeasts inhibited the plant and honeybee pathogens, promoted the growth of A. thaliana seedlings, and induced JA signaling. Microbial VOCs emitted by all tested isolates promoted lateral root formation and increased plant biomass. Collectively, our findings highlight the selectivity of avocado nectar over its microbiota, which could directly impact plant fitness and contribute to the health of its pollinators.

Abstract Using trees tolerant to drought and Phytophthora cinnamomi ( Pc ) infection is the most promising approach to restore Quercus suber and Q. ilex forests under decline. Breeding programs require heritability estimates for tolerance to combined stress. Moreover, the genetic variation underlying genotype-by-environment ( G × E ) interactions in oak tolerance to combined stress has not been explored. We evaluated life expectancy of approximately 10,400 seedlings from 87 Q. suber and 90 Q. ilex half-sib families from Spain under Pc , Pc + drought, and drought + Pc scenarios. Intraspecific variation in tolerance across scenarios, additive genetic variance, and G × E interactions were analyzed. To ensure optimal selection strategies, family genotypic stability was quantified. Under well-watered conditions, Q. suber showed higher tolerance than Q. ilex to Pc , but under the Pc + drought scenario, mortality was similar between species. Geographic variation was detected in cork oak, with populations from eastern Spain showing greater susceptibility. Both species exhibited significant additive genetic variation under the Pc and Pc + drought scenarios, and narrow-sense heritability estimates ( h i 2 ) ranged from 0.10 to 0.16, indicating potential for selective breeding. We report a relevant G × E interaction, primarily due to family rank changes across scenarios. Genotypic stability analyses enabled selection of families with increased and stable tolerance, and the Pc + drought scenario was deemed optimal for selection. A backward selection strategy targeting the 20% most tolerant parents would allow genetic gains of 18% in both oak species. This is the first time oaks have been screened for enhanced and stable tolerance to combined stress.

An environmentally friendly extraction strategy based on an MSAT (Medium Scale Ambient Temperature) system was applied to Quercus ilex and Quercus robur acorns with the aim of maximizing polyphenolic yield and antioxidant activity while minimizing solvent consumption. Operational parameters were first optimized for Quercus ilex using a BBD-RSM (Box-Behnken response surface methodology), where the optimum working zone corresponds to the values of 200 g of acorn, 100 mL of extracting solvent, and 0.5 dispersant/acorn ratio. Subsequently, these conditions were applied to Quercus robur to enable an interspecific comparison. Extracts were evaluated in terms of total polyphenolic content, antioxidant activity, reducing sugars, proteins, targeted polyphenols quantified by UHPLC-QToF, and antimicrobial activity. Optimal extractions from Quercus ilex reached 25,072 mgGAE L-1 and 162 mmolTE L-1, while Quercus robur extracts showed markedly superior values of 35,822 mgGAE L-1 and 234 mmolTE L-1. Polyphenol quantification revealed higher concentrations of gallotannins in Quercus robur and procyanidins and catechin in Quercus ilex. The extracts showed strong antibacterial activity, especially Quercus ilex against S. aureus with a MIC ≤ 0.63%. Furthermore, it has been demonstrated for the first time that acorn extracts can inhibit the growth of Phytophthora cinnamomi in vitro, with Quercus robur extracts having a MIC ≤ 0.1% and Quercus ilex extracts ≤ 1%.

Castanea sativa, a species of high ecological and economic relevance in Europe, faces severe threats from root rot caused by Phytophthora cinnamomi. To explore genetic strategies for enhancing disease tolerance, we investigated the functional role of a chestnut gene homologous to Ginkgo biloba's ginkbilobin-2 (Cast_Gnk2-like), known for its antifungal properties. Using Agrobacterium tumefaciens-mediated transformation, the Cast_Gnk2-like gene was introduced into somatic embryos from two embryogenic chestnut lines. Transformation efficiency was genotype-dependent, and varied from 14.2% to 2.5%. Twelve independent transgenic lines were confirmed by PCR, and each was estimated to carry a single copy of the transgene. Gene expression analysis revealed significant Cast_Gnk2-like transcript levels in two transgenic lines. Following cold storage and germination treatment, viable transgenic plants were regenerated. Disease tolerance assays demonstrated that Cast_Gnk2-like overexpression significantly reduced root necrosis and symptom severity, indicating enhanced tolerance to P. cinnamomi. These findings highlight the potential of targeted gene overexpression to improve disease resilience in chestnut through genetic engineering.

The survival of Quercus species in the Mediterranean region is challenged by root diseases caused by Phytophthora cinnamomi Rands and Pythium spiculum Paul, as well as by drought. This study aimed to examine the interaction between both pathogens under varying soil moisture levels. Seedlings were inoculated with P. cinnamomi, Py. spiculum, or both, and exposed to soil moisture conditions ranging from saturation to drought. Results showed that P. cinnamomi caused high levels of root necrosis in saturated-to-moderately dry soils, but it was unable to cause infection under drought conditions. Conversely, Py. spiculum infected roots under drought but not under saturation conditions and was less virulent in wet soils compared to P. cinnamomi. In seedlings inoculated with both pathogens, symptoms were similar to those induced by P. cinnamomi alone, without any synergistic effect. This study highlights that P. cinnamomi and Py. spiculum infect oak roots across a range of soil moistures, with P. cinnamomi being the predominant pathogen in wet-to-moderately dry soils, and Py. spiculum being the predominant pathogen in droughted soils. Under current and projected future water deficit conditions, oak woodlands infected by both pathogens face a significant threat to their survival.

Phytophthora cinnamomi is a globally important soilborne Oomycete plant pathogen with an extensive and diverse host range, including numerous tree species and woody ornamental plants, and has disrupted forest ecosystems on multiple continents. Members of the Gordonieae tribe, in the family Theaceae, exhibit varying degrees of susceptibility to P. cinnamomi, with Franklinia alatamaha likely being extinct in nature because it is very susceptible to this pathogen. In contrast, Gordonia lasianthus, or loblolly bay, was previously considered resistant when compared to other Gordonieae species. However, in 2019, bleeding cankers were observed on the lower trunk of mature G. lasianthus trees in a coastal forest in South Carolina, in an area that experienced extensive flooding likely due to a recent hurricane and anthropogenic development. This study demonstrates how prolonged exposure to flooded soil conditions significantly increased susceptibility of G. lasianthus to P. cinnamomi and led to severe symptoms of wilting, defoliation, and mortality. It also suggests how host-pathogen interactions involving species of Phytophthora may shift in the future because of climate change and increased frequency of extreme weather events.

The article presents the results of a comprehensive phytopathological analysis of highbush blueberry (Vaccinium corymbosum L.) plantations under the conditions of the Steppe zone of Ukraine. The aim of the study was to identify the main fungal pathogens of the crop, determine their prevalence, and assess the resistance of different cultivars to infection. Experimental research was carried out on a trial plot planted with the cultivars ‘Duke’, ‘Bonus’, ‘Spartan’, ‘Toro’, ‘Chandler’, ‘Bluecrop’, ‘Bluegold’, and ‘Nelson’. The experimental layout was established at a spacing of 1×2.5 m using certified planting material. As a result of field surveys and visual phytopathological diagnostics, it was found that the phytopathogenic complex of blueberry in Steppe conditions is mainly represented by the following fungi: Phytophthora cinnamomi Rands – the causal agent of root rot; Monilinia vaccinii-corymbosi Reade Honey – the causal agent of moniliosis; Colletotrichum gloeosporioides (Penz.) and C. acutatum – causal agents of anthracnose; Septoria albopunctata Cooke – the causal agent of septoriosis; Botrytis cinerea Pers. – the causal agent of gray mold; Phomopsis vaccinii Shear – the causal agent of stem blight. These pathogens infect all major vegetative and generative organs of the plants. Such a wide spectrum of infections indicates the formation of a polyetiological phytopathogenic complex that determines the overall phytosanitary pressure and necessitates the implementation of integrated protection systems for blueberries in the agrocenoses of the Steppe zone. According to the results, the disease development index for gray mold ranged from 2 to 9.5%, for anthracnose – from 9.5 to 16%, for root rot – from 0 to 16%, for moniliosis – from 0 to 19.5%, for septoriosis – from 0 to 12.5%, and for stem blight – from 4 to 12%. The cultivars ‘Duke’ and ‘Chandler’ demonstrated the highest tolerance to the complex of fungal infections, while ‘Toro’ and ‘Bonus’ were the most susceptible. The obtained results indicate the adaptive variability of highbush blueberry cultivars to the conditions of the Steppe zone of Ukraine. The conducted study provides the first generalization of data on the distribution and intensity of key fungal diseases of highbush blueberry in non-typical growing conditions for the crop, which determines its scientific and practical significance for the further development of berry cultivation in Steppe regions.