Advancing Sustainable Management of Bacterial Spot of Peaches: Insights into Xanthomonas arboricola pv. pruni Pathogenicity and Control Strategies

Abstract

Peach (Prunus persica) is a fruit crop of significant economic and cultural value, particularly in Japan, where it is cherished for its symbolism of summer and high quality. However, its production is threatened by bacterial spot caused by Xanthomonas arboricola pv. pruni (Xap), a pathogen that also affects other Prunus species such as nectarines, plums, apricots, and almonds. Xap thrives in warm, humid environments and causes symptoms such as water-soaked lesions, necrotic spots, premature defoliation, and fruit blemishes, leading to reduced yield and marketability. Traditional control methods, including copper-based bactericides and antibiotics, are increasingly ineffective due to resistance development and environmental concerns. This review focuses on the biology, epidemiology, and pathogenic mechanisms of Xap, with particular emphasis on its impact on peach production in Japan. We discuss various disease management strategies, such as integrated disease management, biostimulants, cellulose nanofibers, plant defense activators, and biological control agents, alongside novel molecular approaches targeting bacterial virulence factors. By incorporating these innovative and eco-friendly methods with traditional practices, this review offers insights into the potential for sustainable, environmentally friendly solutions to manage bacterial spot and mitigate its impact on peach production.

1. Introduction

Peach (Prunus persica (L.) Batsch) is one of the most economically and culturally important fruit crops globally, and its cultivation spans across diverse climatic regions, with a global yield of 24.2 million tons in 2022/23 [1]. However, peach production faces significant challenges due to various biotic stresses, especially bacterial spot caused by Xanthomonas arboricola pv. pruni (Xap) (Smith 1903) Vauterin, Hoste, Kersters and Swings 1995 [2,3]. Xap is a quarantine pathogen responsible for bacterial spot, representing a significant threat to global peach production [2]. This pathogen also affects other Prunus species, including nectarines, plums, apricots, and almonds, but peaches and nectarines are especially susceptible [2]. The disease manifests as water-soaked lesions on leaves, stems, and fruits, which later become necrotic, leading to premature fruit drop and reduced fruit quality [3,4]. In severe infection, it can cause extensive defoliation, resulting in reduced photosynthesis and overall plant vigor. The disease can lead to considerable yield losses and diminished fruit marketability due to the unsightly lesions and the increased susceptibility of affected plants to secondary infections [3,4].

Traditional management strategies for Xap have relied heavily on copper-based bactericides and streptomycin, but these have become less effective over time due to the development of resistant strains and increasing restrictions on antibiotic use in agriculture [5,6,7,8]. Moreover, the environmental impact of copper accumulation in orchard soils has led to growing concern about the sustainability of such chemical control measures. In response, researchers and growers have studied alternative management strategies, including integrated disease management (IDM) and biological control agents. Although recent genomic and phenotypic studies have identified potential virulence factors [9], the specific mechanisms related to host specificity and the infection process are poorly understood so far. Understanding these molecular interactions is critical for the development of novel and effective control strategies, such as effector-based resistance breeding and the disruption of bacterial virulence systems.

This review provides a comprehensive exploration of the current knowledge on Xap, with an emphasis on its significant impact on peach production. It explores the biology, epidemiology, and pathogenicity mechanisms of Xap. The review also addresses the challenges posed by the limitations of traditional chemical control methods, such as copper-based bactericides and antibiotics, which are increasingly ineffective due to resistance development and environmental concerns. In response to these challenges, the review highlights a variety of alternative strategies for managing Xap, including IDM, biostimulants, cellulose nanofibers, plant defense activators, biological control, and antivirulence strategies.

2. Impact of Bacterial Spot

Bacterial spot of peaches caused by Xap severely impacts fruit quality and orchard productivity worldwide. Infected orchards experience reduced marketability of fruits, increased management costs, and significant yield losses. For example, in the United States, 25–75% of fruits could show lesions in abandoned peach orchards, while South America has faced severe losses in susceptible peach and nectarine cultivars [10]. An epidemic in a commercial plum orchard of northern Italy is affecting 30% of the fruits [3]. Beyond fruit crops, Xap has also disrupted ornamental plant nurseries, particularly cherry laurel production for international markets in the Netherlands [11].

In Japan, Xap outbreaks have caused increasing damage in peach-producing regions such as Yamanashi, Fukushima, and Nagano prefectures, which are responsible for a large portion of Japan high-quality peach exports [12,13]. The warm, humid conditions during the rainy season create an ideal environment for disease development, leading to significant yield losses and reduced fruit quality [12,13]. Kawaguchi [14] showed that bacterial spot incidence ranged from 5.4 to 75.9% over 12 years in Okayama, while high production costs arise from the need for chemical treatments, pruning, and orchard sanitation [14]. Despite efforts using rain shelters and integrated disease management practices, economic losses remain substantial [15,16].

3. Disease Symptoms and Host Range

Xap causes bacterial spot on a wide range of Prunus species, including peaches and nectarines (Prunus persica), plums (Prunus domestica), apricots (Prunus armeniaca), cherries (Prunus avium), and almonds (Prunus dulcis) [3]. Susceptibility varies among Prunus species, with peaches and nectarines (P. persica), almond (P. dulcis), cherry (P. cerasifera), and blackthorn (P. spinosa) being highly susceptible, while mahaleb cherry (P. mahaleb), sour cherry (P. cerasus), and sweet cherry (P. avium) show low susceptibility [17]. Interestingly, European ground cherry (P. fruticosa) exhibits immunity to Xap [17]. Symptoms vary depending on the environmental conditions, cultivar susceptibility, and infection timing.

In Japan, bacterial spot has become a significant issue, particularly for peach cultivation. Symptoms in peaches affect all above-ground parts including leaves, twigs, and fruits. On leaves, early signs include small water-soaked lesions that enlarge, turn necrotic and develop yellow halos [18] (Figure 1A). Twig infections appear as necrotic cankers, which may girdle branches and weaken the tree (Figure 1B,C). One-year-old twigs often become infected in spring (Figure 1B), which can spread to leaves (Figure 1A), new shoots (Figure 1C), and fruits (Figure 1D). Therefore, removing infected one-year-old twigs is highly recommended to reduce disease severity [12]. On fruits, small brown, sunken spots develop, which later become necrotic and may coalesce, rendering the fruit unmarketable (Figure 1D).

4. Epidemiology and Disease Cycle in Peach Orchards

Xap thrives under optimal conditions of 20–30 °C and high humidity [19]. The Xap global distribution spans Asia, Europe, the Americas, and Oceania, with evidence suggesting a recent spread from the United States, given its low genetic diversity across regions [20]. At short distances, Xap spreads among trees and nearby plots by rain, wind, and contaminated pruning or machinery [2]. The ability of Xap to survive epiphytically and in a latent phase further complicates its detection and management [21].

Peach cultivation in Japan is heavily influenced by the seasonal climate, which plays a crucial role in the proliferation of Xap. During the winter dormancy period (November to March), the pathogen survives in infected plant tissues such as leaf scars, bud scales, and cankers, entering a quiescent state and serving as the primary source of infection for the next growing season [22]. Dormant pruning is critical in removing these inoculum sources, but incomplete pruning can leave reservoirs for the pathogen, a challenge faced globally [2]. Xap can also grow epiphytically on non-host plants like citrus and weeds, complicating disease management as these plants serve as alternative inoculum sources [23].

As spring arrives, Xap becomes active when peach trees break dormancy such as bud break and leaf emergence. Rain splashes and wind-driven rain spread the bacteria, infecting young tissues through natural openings or wounds, a process seen worldwide [15,19]. From late spring to early summer, the rainy season in Japan creates optimal conditions for Xap, with June rainfall playing a critical role in disease severity, promoting bacterial multiplication.

Kawaguchi [14] reported that the incidence of bacterial spot at harvest is more strongly influenced by the overwintering density of the pathogen than by the weather conditions during the current growing season. As summer progresses, late-season infections present a challenge due to restrictions on chemical applications near harvest, but early-season bactericide applications and post-harvest sanitation practices, such as removing fallen leaves and infected branches, help mitigate risks and reduce overwintering inoculum levels.

5. Virulence Factors in Xap

A central component of Xap pathogenicity is the type III secretion system (T3SS), encoded by hrp/hrc genes. Acting as a molecular syringe, the T3SS injects effector proteins (T3Es) into host cells, manipulating immune responses and facilitating infection [24]. Pathogenic strains, such as Xap, possess a larger and more diverse T3E repertoire compared to non-pathogenic strains, reflecting their enhanced virulence and adaptability [25]. Genomic analyses have revealed that non-virulent Xap strains isolated from Prunus spp. lack canonical T3SS components and exhibit reduced T3E repertoires, including the absence of key effectors such as XopAI and XopE3, which are crucial for host specificity and virulence in Xap [26]. Recent work by Sakata et al. [27] demonstrated that mutants of critical T3SS components, such as HrcC and HrcV, showed significantly reduced virulence in inoculation assays using detached peach leaves, further confirming the indispensable role of the T3SS in Xap pathogenicity. The host specificity of Xap is further influenced by its genetic plasticity and the presence of virulence-associated elements. Multilocus sequence analysis and pan-genomic studies indicate that non-virulent strains cluster with low-virulence strains from diverse hosts, such as banana and barley, highlighting the importance of gene acquisition and loss in host-specific pathogenicity [26]. A key determinant of Xap pathogenicity is the plasmid pXap41, which carries important T3E genes and other virulence factors. The absence of this plasmid in non-pathogenic strains underscores the critical role of horizontal gene transfer in the evolution of virulence [26]. Together, these findings illustrate how the interplay between the T3SS, virulence factors, and genetic plasticity shapes the pathogenic potential and host specificity of Xap.

In addition to the T3SS, other mechanisms contribute to the virulence of Xap. The Type II (T2SS) and Type VI (T6SS) secretion systems play crucial roles in the release of enzymes and proteins that assist in host tissue degradation and immune evasion [24] Pathogenic strains of Xap exhibit distinctive profiles of cellulases, xylanases, and lipases, which enhance their ability to degrade plant cell walls, an important step in tissue invasion and disease progression [24].

The role of motility in Xap pathogenicity was highlighted by Sakata et al. [27]. The fliD gene encodes the flagellar cap protein, which is essential for the assembly and functionality of the flagellar filament. fliD mutants exhibited reduced motility and significantly reduced virulence in host plants. These findings highlight the critical role of fliD and flagellar motility in the infection process, positioning fliD as a potential target for novel disease management strategies. Although several key virulence factors have been identified, the specific roles remain unclear and requires further investigation.

6. Management Strategies

Chemical control has long been the cornerstone of Xap management, with copper-based treatments, such as copper hydroxide and copper sulfate, widely used to reduce bacterial populations on plant surfaces. However, the emergence of copper-tolerant Xap strains in peach orchards has reduced the efficacy of these treatments in some regions [5,6,7]. Despite these challenges, studies in Japan and elsewhere demonstrated that copper treatments, when combined with other strategies, remain effective for managing early infections. The integration of zinc-based compounds and plant elicitor peptides offers promising alternatives to reduce reliance on copper [28].

Antibiotic treatments, such as streptomycin and oxytetracycline, have also played a role in Xap control. However, streptomycin resistance has become a significant issue in Japan, with studies reporting high resistance frequency among Xap isolates in regions such as Fukushima and Wakayama [8]. This resistance is linked to specific mutations in the rpsL gene, which confer varying levels of tolerance. Recent genomic studies have expanded on this, identifying the genetic basis for resistance to both streptomycin and oxytetracycline in Xap populations [7]. These studies revealed the presence of mobile genetic elements, such as plasmids carrying resistance genes, which can be transferred between bacterial populations, potentially accelerating the spread of antibiotic resistance [7]. Although oxytetracycline has remained effective against Xap, oxytetracycline-resistant strains are already present in South Carolina [7], raising concerns about the continued effectiveness of these antibiotics. In field trials involving several chemical treatments in China, the copper-based bactericide Kocide and the dithiocarbamate fungicide Mancozeb showed particularly strong efficacy against Xap, with disease suppression rates of 47% and 80%, respectively [29]. Nonetheless, the increasing prevalence of antibiotic resistance in Xap populations raises significant concerns about the sustainability of relying on streptomycin and oxytetracycline for disease control. These findings highlight the urgent need to incorporate alternative strategies, such as the use of biocontrol agents, resistance inducers, and integrated management practices, to reduce dependency on antibiotics and mitigate the risk of resistance development [7].

Cultural practices are a critical component of IDM, focusing on improving orchard hygiene and modifying environmental conditions to limit pathogen survival and spread. Sanitation measures, such as removing and destroying infected plant material during the dormant season, significantly reduce overwintering inoculum. For example, Kawaguchi et al. [15] demonstrated that early removal of spring cankers lowers primary infection sources and improves disease control during fruit ripening. Proper pruning and canopy management enhance air circulation, reducing humidity levels that favor bacterial growth. Rain-protected cultivation, combined with appropriate irrigation practices, such as switching from overhead to drip systems, has further reduced infection rates in Japanese orchards [13].

The development of resistant cultivars represents a long-term solution to managing bacterial spot. Although no peach cultivars are completely immune to Xap, breeding programs are focusing on identifying and incorporating partial resistance traits into commercially viable varieties. Advances in genomic tools and marker-assisted selection have significantly accelerated this process. For instance, Suesada et al. [30] used quantitative trait loci (QTL) mapping to identify genetic markers associated with partial resistance to Xap in peach breeding populations. These insights have guided the development of resistant cultivars, offering growers an additional tool to mitigate disease impact.

Accurate detection and monitoring are crucial for managing Xap. Real-time PCR (polymerase chain reaction) protocols enable early and reliable detection in symptomatic and asymptomatic plant material, allowing timely interventions to prevent disease spread [21]. A significant advancement is a PCR method using hrp gene-based primers, which ensures rapid, specific, and highly accurate detection of Xap by targeting genes critical to its pathogenicity [31]. Building on these developments, a long-amplicon propidium monoazide-quantitative PCR (PMA-qPCR) assay has been designed to detect viable Xap cells. This method improves accuracy by distinguishing live bacteria from dead ones, offering precise insights into pathogen activity and aiding targeted management strategies [32]. Additionally, loop-mediated isothermal amplification (LAMP) provides a rapid, sensitive, and equipment-free approach for detecting Xap, making it ideal for on-site diagnostics and resource-limited settings [33]. Advanced forecasting models, such as the hierarchical Bayesian model (HBM) by Kawaguchi and Nanaumi [34], integrate environmental data to predict disease incidence. When combined with detection tools like hrp-based PCR, PMA-qPCR, and LAMP, these models create a robust framework for early detection, precise monitoring, and proactive management.

In conclusion, managing bacterial spot caused by Xap requires a multifaceted approach that integrates chemical treatments, agricultural practices, resistant cultivars, and advanced detection and forecasting tools. While copper-based bactericides and antibiotics remain effective components of disease management, resistance development underscores the importance of diversifying control strategies. By adopting IDM frameworks tailored to regional conditions and leveraging advances in technology and breeding, growers can mitigate the economic impact of Xap and ensure sustainable stone fruit production.

7. Future Perspectives

The management of bacterial spot caused by Xap is increasingly challenging due to rising concerns over the environmental impact and efficacy of traditional chemical treatments, such as copper-based bactericides and antibiotics. The development of resistant strains and the strict regulation of chemical use in agriculture necessitate the exploration of innovative and sustainable disease management strategies. In this review, we introduced potential chemicals and other materials, including antivirulence compounds, biostimulants, amino acids, defense activators, and cellulose nanofibers, as novel control strategies.

Recent advances in understanding the pathogenicity mechanisms of plant bacteria have opened new avenues for targeted control strategies that do not rely on traditional bactericidal approaches. Structure-based design of antivirulence compounds leverages the 3D structures of bacterial virulence factors to identify potential targets that can inhibit their activity. Unlike conventional antibiotics, which aim to kill or inhibit the growth of pathogens, antivirulence compounds work by disarming the pathogen, preventing it from causing disease. By neutralizing key mechanisms, such as toxin production, adhesion, or immune evasion, this approach reduces the bacterial ability to infect plants, minimizing disease severity without the use of harsh chemicals [35,36,37,38]. Pseudomonas aeruginosa is a well-known opportunistic pathogen that causes infections in humans and exhibits high levels of antibiotic resistance, highlighting the need for research into antivirulence strategies as potential therapeutic alternatives [39,40]. Antivirulence strategies target virulence factors such as quorum sensing, T3SS, biofilms, and flagella, aiming to disarm the pathogen without inducing resistance [41,42]. These compounds work by reducing pathogenicity without promoting bacterial resistance, providing valuable insights into the development of antivirulence compounds. This progress in P. aeruginosa highlights the potential for similar strategies in plant pathogenic bacteria, although the application of structure-based antivirulence compound design to plant pathogens has not yet been fully realized. An important aspect of antivirulence compound development is the selection of appropriate bacterial virulence factors to target. This requires identifying and validating factors essential for the disease process. To select these factors, screening using mutant strains of bacteria is critical, as it allows the identification of genes involved in virulence. In the case of plant pathogenic Pseudomonas species, extensive screening has already been conducted, leading to the identification of a variety of virulence factors responsible for pathogenicity [43,44,45,46]. Similarly, in Xanthomonas species, significant progress has been made in identifying virulence factors through high-throughput mutant screening. In X. citri subsp. citri, 59 putative virulence-related genes were identified, including 27 novel genes [47]. Similarly, screening of X. campestris pv. campestris mutants revealed virulence factors involved in metabolic pathways, regulatory systems, and secretion systems [48]. For X. oryzae pv. oryzicola, seven candidate virulence genes were identified, including opgH, purF, thrC, trpA, and three hypothetical proteins [49]. Further studies on X. oryzae pv. oryzicola uncovered novel virulence factors, some of which were previously associated with animal pathogens [50]. These studies have expanded our understanding of Xanthomonas pathogenicity mechanisms, laying the groundwork for targeted antivirulence compound development. However, the virulence factors and infection mechanisms of Xap remain largely unknown. Understanding these mechanisms is crucial for developing effective strategies for managing Xap. Moving forward, identifying the key virulence factors involved in Xap pathogenicity and applying structure-based design approaches to target these factors will be essential for developing antivirulence compounds that can reduce the severity of Xap infections while offering sustainable alternatives to traditional chemical treatments. Regulatory hurdles for antivirulence compounds, along with the high cost of scaling up biocontrol strategies in smallholder orchards, should also be carefully considered.

Biostimulants, which are biological formulations designed to enhance plant growth, nutrient uptake, and stress tolerance, have gained significant attention in disease management due to their natural origin and low toxicity [51]. Among these, amino acids are particularly notable for their ability to promote plant growth and bolster resilience against a variety of stressors. Certain amino acids, such as proline, glutamic acid, and glycine, play crucial roles in helping plants withstand both abiotic and biotic stresses by improving osmotic regulation, enhancing antioxidant activity, and stabilizing cellular structures under adverse conditions [52,53,54]. Several studies have highlighted the potential of amino acids to induce resistance against Xanthomonas infections in plants. For instance, in lime plants, treatment with L-methionine significantly enhanced resistance to citrus canker caused by X. citri subsp. citri by increasing antioxidant enzyme activity. The lesion size was reduced by approximately 78.5% compared to the water control [55]. Similarly, Safaie Farahani and Taghavi [56] demonstrated that β-aminobutyric acid (BABA) induced resistance in pepper plants against X. euvesicatoria by promoting catalase activity and the expression of pathogenesis-related protein (PR) 1 [56]. These findings suggested that amino acid treatments hold promise as environmentally friendly strategies for managing Xanthomonas infections in diverse crop plants. While much of the current research has focused on other Xanthomonas species, the demonstrated ability of amino acids to enhance plant resistance and mitigate disease severity indicates their potential applicability to managing Xap. Further studies are warranted to explore the efficacy of amino acid-based treatments in reducing Xap infections, which can provide an innovative and sustainable approach to controlling bacterial spot in peach and other Prunus species.

In addition to amino acids, certain peptides have also been shown to induce resistance against Xap in plants. For example, plant elicitor peptides (Peps) derived from P. persica, such as PpPep1 and PpPep2, were found to enhance resistance to Xap in peach plants by triggering transcriptomic reprogramming and activating defense mechanisms [57]. Similarly, Rosaceae-derived Peps have been shown to effectively control Xap in Prunus species at nanomolar concentrations [28]. Future research should focus on optimizing amino acid and peptide-based treatments for sustainable management of Xap. Identifying the molecular mechanisms by which these compounds enhance plant defenses, including systemic acquired resistance and hormonal signaling, will enable more targeted applications. Peps also hold promise, with further studies needed to refine application methods for field conditions. Integrating these approaches into broader pest management frameworks can reduce reliance on chemical controls, providing an environmentally friendly solution for Xap management.

Biological control offers sustainable alternatives to chemical treatments, utilizing naturally occurring or introduced organisms to suppress pathogens. Bacillus strains have shown effectiveness for controlling citrus bacterial canker caused by X. citri subsp. citri [58]. The Bacillus strains reduced the disease symptoms by 26.3% and pathogen density by approximately 82% compared to the control [58]. Bacteriophages have also emerged as promising biocontrol agents, successfully controlling X. campestris pv. vesicatoria and X.citri subsp. citri [59]. Phage-based treatments have demonstrated efficacy at different stages of disease development, including seed decontamination and field applications [59]. Kawaguchi et al. [15] explored the use of nonpathogenic Xanthomonas strains (AZ98101 and AZ98106) as biocontrol agents for bacterial spot of peach. Field trials showed that these strains could suppress disease under high-pressure conditions, with AZ98101 persisting on fruit and leaves for up to 12 days post-application. While these findings highlight the potential of nonpathogenic Xanthomonas strains, further optimization is needed to determine the best application methods, dosages, and timings to improve efficacy. Additionally, understanding their interaction with plant defense mechanisms can enhance their effectiveness. Long-term field trials across diverse environmental conditions are essential to assess their practical viability and establish their role in comprehensive bacterial spot management strategies.

Plant defense activators are compounds that enhance plant natural defense mechanisms against pathogens by triggering immune responses rather than directly targeting the pathogen [60]. These activators provide an environmentally friendly alternative to traditional chemical pesticides by strengthening plant resilience. Acibenzolar-S-methyl (ASM), a well-known plant defense activator, has demonstrated broad-spectrum efficacy against bacterial diseases, including Pseudomonas and Xanthomonas species. In Pseudomonas infections, ASM has been extensively studied and is known to activate systemic acquired resistance and defense-related genes, effectively reducing disease severity in multiple plant hosts. Its mechanisms in managing Pseudomonas diseases have been particularly well-characterized [61,62], offering insights into its potential for controlling other bacterial pathogens. For Xanthomonas infections, ASM has been shown to effectively induce resistance in various crops. In lettuce, ASM reduced bacterial speck disease severity caused by X. campestris pv. vitians and increased chitinase activity [63]. In rice, ASM pretreatment significantly suppressed bacterial leaf blight symptoms caused by X. oryzae pv. oryzae, while increasing the phenolic content and expression of pathogenesis-related proteins [64]. Additionally, in tomatoes, ASM provided 49.3% protection against X. vesicatoria and enhanced peroxidase and polyphenol oxidase activities [65]. These findings highlight ASM versatility and efficacy in managing bacterial pathogens by activating key defense mechanisms across diverse plant species. Future research should focus on optimizing the use of defense activators such as ASM for Xap management. Exploring their molecular mechanisms and integrating them with sustainable strategies, such as biological control, can enhance efficacy and reduce chemical pesticide reliance.

Cellulose nanofiber, derived from cellulose, is a plant-based and renewable material with nanoscale dimensions. Cellulose nanofiber has been shown to alter the hydrophobicity of leaf surfaces, providing a physical barrier that can prevent fungal pathogen entry, as demonstrated in previous studies with Phakopsora pachyrhizi, the causal agent of Asian soybean rust [66]. More recently, cellulose nanofiber has been explored as a potential management tool for bacterial diseases, including bacterial blight caused by Pseudomonas cannabina pv. alisalensis (Pcal) [67]. The application of cellulose nanofiber to cabbage leaves suppressed disease symptoms by reducing bacterial populations and entry, along with the downregulation of virulence-related genes, such as those encoding type III effectors, coronatine biosynthesis, and flagellar proteins in Pcal [67]. These findings suggest that cellulose nanofiber alters leaf surface properties, which in turn affects bacterial behaviors and reduces disease development. Kusakabe [68] evaluated cellulose nanofiber efficacy against Xap on peach trees, finding that cellulose nanofiber application achieved 85.0% control efficacy, comparable to 82.6% for oxytetracycline in the field. These results highlight the potential of cellulose nanofiber for sustainable disease management, particularly when combined with other eco-friendly approaches such as biological control agents or physical treatments. Future research should focus on optimizing the use of cellulose nanofiber treatments for Xap management. Investigating the precise mechanisms by which cellulose nanofiber alters leaf surface properties and modulates Xap behavior will provide deeper insights into its potential applications. For the practical application of cellulose nanofibers, scalability challenges such as production costs and appropriate application methods need to be addressed.

8. Conclusions

The management of bacterial spot caused by Xap represents a critical challenge for peach production globally, particularly in regions such as Japan, where high-quality peaches are economically and culturally significant. The increasing limitations of chemical controls due to resistance development and environmental concerns underscore the need for sustainable and innovative solutions. Advances in molecular biology and genomics have revealed critical insights into Xap pathogenicity, opening pathways for targeted antivirulence strategies and resistance breeding. Emerging approaches such as the use of cellulose nanofibers, biostimulants, and plant defense activators offer promising eco-friendly alternatives that complement traditional practices. To ensure long-term success, research must focus on integrating these novel strategies into comprehensive IDM systems, optimizing their efficacy under diverse environmental conditions. By prioritizing sustainability, adaptability, and scientific innovation, the agricultural industry can mitigate the economic and ecological impacts of Xap, ensuring the viability of peach production for future generations.