Survey of Plant Diseases in Horticultural Crops in Cheorwon, South Korea, in 2024

Survey area and sample collection.

A field survey was conducted from January to October 2024 across six administrative districts of Cheorwon-gun: Galmal-eup, Geunnam-myeon, Gimhwa-eup, Dongsong-eup, Seo-myeon, and Cheorwon-eup. In collaboration with the Cheorwon Agricultural Technology Center, symptomatic samples were collected from eight major horticultural crops cultivated in the region, including paprika, tomato, chili pepper, green pepper, cucumber, zucchini squash, melon, and mini watermelon. A total of 177 plant samples exhibiting disease symptoms were collected and subjected to molecular analysis (Fig. 1A).

Fig. 1.

Overview of plant disease occurrence by region, pathogen type, and dominant species detected in horticultural crops of Cheorwon-gun. (A) Regional distribution and infection status of surveyed farms in Cheorwon-gun; (B) number of farms with fungal, bacterial, and viral diseases, including co-infected cases; and (C) distribution of detected fungi, bacteria, and viruses in positive farms. BBWV2, broad bean wilt virus 2; CGMMV, cucumber green mottle mosaic virus; CMV, cucumber mosaic virus; PepMoV, pepper mottle virus; PMMoV, pepper mild mottle virus; TSWV, tomato spotted wilt virus; WMV, watermelon mosaic virus.

PCR detection of fungal and bacterial pathogens.

For the diagnosis of fungal and bacterial diseases, PCR was performed targeting seven fungal pathogens (A. solani, B. cinerea, F. oxysporum, S. sclerotiorum, P. capsici, P. infestans, and P. ultimum) and three bacterial pathogens (C. michiganensis, P. carotovorum, and R. solanacearum). DNA was extracted from the symptomatic plant tissues using the Biocube Extraction Kit (Biocubesystem, Suwon, Korea) according to the manufacturer's protocol. The template DNA was absorbed into a porous ceramic Biocube prior to amplification.

Each 20 µl PCR reaction contained 10 µl of 2X PCR master mix, 1 µl each of forward and reverse primers (10 pmol), and 8 µl of distilled water. One Biocube was placed into each reaction tube. PCR cycling conditions were as follows: initial denaturation at 95°C for 5 min; 35 cycles of denaturation at 95°C for 30 sec, annealing at 55-65°C for 30 sec (depending on primer), and extension at 72°C for 1 min; and a final extension at 72°C for 5 min. Primer sequences and specific reaction conditions are summarized in Table 1.

Table 1.

Primer sequences and PCR/RT-PCR conditions for detection of fungal, bacterial, and viral pathogens

RT-PCR detection of viral pathogens.

Seven RNA viruses (BBWV2, CMV, PepMoV, PMMoV, TSWV, CGMMV, and WMV) were detected using RT-PCR. Total RNA was extracted using the Biocube Extraction Kit and prepared following the same Biocube-based protocol as for DNA extraction. Each 20 µl RT-PCR reaction consisted of 10 µl of BCS RT-PCR 2X master mix (for virus detection), 1 µl each of forward and reverse primers (10 pmol), and 8 µl of distilled water. Reverse transcription was carried out at 48°C for 5 min, followed by PCR amplification using the same cycling protocol as for DNA templates. Specific primers used for each viral target are listed in Table 1.

Disease incidence by region and crop.

Between January and October 2024, plant pathogenic microorganisms were detected in 52 of the 86 surveyed farms (60.47%) across Cheorwon-gun. Pathogen detection was highest in Geunnam-myeon (13 out of 24 farms) and Dongsong-eup (14 out of 23 farms). Other regions such as Gimhwa-eup (9 out of 13), Seo-myeon (8 out of 13), Galmal-eup (6 out of 11), and Cheorwon-eup (2 out of 2) also reported positive detections (Fig. 1A).

Among pathogen categories, bacterial diseases were most prevalent, detected in 24 farms, followed by fungal diseases in 22 farms and viral infections in 17 farms. Mixed infections were also observed: six farms had co-infection with fungi and bacteria, four farms with fungi and viruses, and one farm with both bacteria and viruses (Fig. 1B).

Crop-wise, fungal diseases were most frequently detected in paprika, bacterial diseases were most common in tomato, and viral infections were primarily found in chili pepper. This trend reflects both host susceptibility and potential environmental and cultivation-related factors influencing pathogen dynamics (Table 2).

Table 2.

Crop-wise occurrence of fungal, bacterial, and viral pathogens in Cheorwon-gun

The most dominant fungal pathogens detected were P. infestans and P. ultimum, while R. solanacearum was the predominant bacterial species, and TSWV was the most frequently detected virus (Fig. 1C). In cases where plant disease symptoms were present but no pathogenic organism was detected, potential causes included abiotic stress such as over-irrigation, fertilizer or chemical misuse, or insect damage caused by small root-feeding gnats or fungus gnats.

Occurrence of fungal diseases.

Fungal pathogens were detected using species-specific PCR targeting seven common soil- and air-borne fungi. P. infestans and P. ultimum were the predominant species, each accounting for 40% of total fungal detections, and primarily associated with paprika, tomato, and chili pepper crops (Table 3). F. oxysporum and P. capsici were each detected at 8.57%, and B. cinerea was identified in 2.86% of fungal cases. A. solani and S. sclerotiorum were not detected in any sample during the survey period.

Table 3.

Pathogen detection frequency by classification and host crop

Regionally, P. infestans was identified in Galmal-eup, Geun-nam-myeon, Gimhwa-eup, Dongsong-eup, and Seo-myeon, while P. ultimum was detected only in Gimhwa-eup and Geunnam-myeon, both located in the eastern part of Cheorwon-gun (Table 4). In Seo-myeon, four fungal pathogens—B. cinerea, F. oxysporum, P. capsici, and P. infestans—were detected, indicating a higher diversity of fungal diseases in this region. In Gimhwa-eup, F. oxysporum, P. infestans, and P. ultimum were present. Geunnam-myeon yielded P. infestans and P. ultimum, whereas Galmal-eup and Dongsong-eup had only P. infestans detections. No fungal pathogens were detected in Cheorwon-eup.

Table 4.

Regional detection summary of plant pathogens across six districts

These regional patterns suggest that P. ultimum may be environmentally restricted or associated with specific cultivation practices found in eastern Cheorwon. The co-occurrence of P. ultimum and P. infestans in crops such as paprika and tomato is concerning, given their potential to spread through wind, irrigation water, and soil. This underscores the need for targeted monitoring and management of P. ultimum in high-risk areas.

Compared to 2023, when F. oxysporum-induced damping-off caused severe economic losses in paprika farms due to seed-borne infections, its reduced prevalence in 2024 suggests improved seed hygiene and management practices. Meanwhile, P. ultimum and P. infestans have emerged as the major fungal threats in the region (Bae et al., 2024). Continued monitoring and region-specific disease control strategies are recommended to prevent future outbreaks.

Occurrence of bacterial diseases.

To investigate the prevalence of bacterial diseases in Cheorwon, PCR diag-nostics targeting C. michiganensis, P. carotovorum, and R. solanacearum were conducted on symptomatic samples collected from January to October 2024 (Tables 3, 4).

Among these, R. solanacearum was the most frequently detected, accounting for 75% of total bacterial detections. This pathogen was found across all six surveyed regions— Cheorwon-eup, Dongsong-eup, Galmal-eup, Geunnam-myeon, Gimhwa-eup, and Seo-myeon—indicating its widespread distribution and strong adaptability to various field conditions. It was detected in a range of crops, including paprika, tomato, chili pepper, and green pepper.

C. michiganensis was the second most prevalent bacterial pathogen (19.44%), detected primarily in tomato, paprika, and green pepper, while P. carotovorum was the least detected (5.56%), found in chili pepper and tomato samples. Notably, C. michiganensis, P. carotovorum and R. solanacearum were all identified in Dongsong-eup and Seo-myeon, suggesting potential hotspots for bacterial disease diversity. In Galmal-eup and Gimhwa-eup, only C. michiganensis and R. solanacearum were detected, while Cheorwon-eup and Geun-nam-myeon exclusively reported R. solanacearum infections.

The dominance of R. solanacearum aligns with its known epidemiological behavior, thriving in high-temperature and high-humidity environments, particularly during the summer season. Its persistence in soil and irrigation water highlights the importance of long-term field sanitation and water management practices. Early detection systems and resistant cultivars should be prioritized in managing this pathogen in Cheorwon.

Occurrence of viral diseases.

Viral pathogens were detected in 17 farms through RT-PCR analysis targeting seven common viruses (BBWV2, CGMMV, CMV, PepMoV, PMMoV, TSWV, and WMV). Among these, TSWV was by far the most prevalent, accounting for 64.86% of viral detections and observed in all six regions of Cheorwon-gun. It was primarily found in paprika, tomato, and chili pepper crops, and its widespread occurrence underscores its adaptability and potential for vector-mediated dissemination (Tables 3, 4).

CMV followed with 10.81% of detections, mainly in chili pepper and zucchini squash. PMMoV, PepMoV, and WMV were detected at 8.11%, 5.41%, and 5.41%, respectively. BBWV2 and CGMMV were the least detected, each accounting for 2.70% of cases (Table 3). Regionally, Geunnam-myeon and Seo-myeon each had four virus detections, including CMV, PepMoV, PMMoV, and TSWV in Geunnam-myeon and CGMMV, CMV, TSWV, and WMV in Seo-myeon. Cheorwon-eup reported BBWV2, PMMoV, and TSWV, while Gimhwa-eup, Galmal-eup, and Dongsong-eup only showed TSWV.

Comparison with a previous survey conducted in 2016 showed consistent detection of TSWV across all regions (Kil et al., 2018). However, CMV incidence has declined, now only appearing in Geunnam-myeon and Seo-myeon, whereas PepMoV, previously undetected, newly emerged in Geun-nam-myeon in 2024. These changes may reflect shifts in vector populations or environmental conditions influencing virus spread.

TSWV was first detected in May, coinciding with the start of thrips activity, and peaked in July when multiple viruses were also found. This seasonal pattern indicates the importance of early vector control to prevent virus establishment and spread in susceptible crops.

Temporal trends and mixed infections.

To evaluate seasonal patterns and co-infection trends, plant disease incidence data from January to October 2024 were analyzed. Fungal pathogens were primarily detected between March and May, peaking in May before declining as temperatures increased. Bacterial pathogens were most prevalent in July and August, coinciding with the hottest and most humid period of the year. Viral pathogens showed the highest detection rates between May and July. Notably, TSWV began appearing in May, aligned with the onset of thrips activity, and a variety of viruses were co-detected in July (Fig. 2).

Fig. 2.

Seasonal detection trends of fungal, bacterial, and viral pathogens in Cheorwon-gun during 2024. (A) Monthly trend of overall plant pathogen detections from January to October 2024 and (B) monthly occurrence patterns of fungal, bacterial, and viral pathogens. BBWV2, broad bean wilt virus 2; CGMMV, cucumber green mottle mosaic virus; CMV, cucumber mosaic virus; PepMoV, pepper mottle virus; PMMoV, pepper mild mottle virus; TSWV, tomato spotted wilt virus; WMV, watermelon mosaic virus.

Mixed infections were found in 16 farms. These included fungal-fungal co-infections (e.g., F. oxysporum + P. infestans), bacterial-bacterial co-infections (C. michiganensis + R. solanacearum), and viral co-infections (e.g., CMV + PepMoV, CMV + CGMMV + WMV). All viral co-infections involved aphid-transmitted viruses, suggesting shared vector path-ways (Fang et al., 2021; Gildow et al., 2008; Moya-Ruiz et al., 2023; Qi et al., 2021) (Table 5).

Table 5.

Summary of mixed infections by pathogen type and combination

The most frequent co-infections occurred between fungal and bacterial pathogens (6 farms), all involving R. solanacearum, primarily with P. capsici or P. infestans. Four fungus-virus co-infections were detected, all involving TSWV along with either P. infestans or P. ultimum. One farm showed a bacterial-virus co-infection including R. solanacearum, BBWV2, PMMoV, and TSWV. No triple co-infections (fungus-bacterium-virus) were observed.

These findings highlight the need to monitor overlapping environmental conditions, pathogen ecology, and vector activity in order to prevent co-infection-driven disease outbreaks. We recommend integrating disease surveillance and control strategies will be critical to mitigate risks in horticultural crop systems.

This study provides a comprehensive overview of plant pathogen occurrence in major horticultural crops across Cheorwon-gun, South Korea, from January to October 2024. Among the 86 farms surveyed, 60.47% tested positive for at least one fungal, bacterial, or viral pathogen. The most frequently detected pathogens were P. ultimum and P. infestans among fungal species, R. solanacearum among bacteria, and TSWV among viruses.

Temporal analysis revealed that fungal pathogens peaked in spring (May), bacterial pathogens during the summer monsoon season (July to August), and viral infections during late spring to early summer (May to July), particularly associated with vector activity. Spatially, R. solanacearum and TSWV were identified in all six surveyed districts, indicating widespread endemicity. Mixed infections, particularly between fungi and bacteria, were frequently observed and may exacerbate disease severity in crops.

These findings emphasize the importance of early diagnosis and proactive management strategies tailored to local climate and cropping conditions. Disease surveillance and integrated pest and disease control systems should consider seasonal pathogen dynamics, co-infection patterns, and regional disease hotspots to minimize economic loss and ensure sustainable horticultural production in Cheorwon-gun.