Crown gall and root gall diseases caused by Agrobacterium spp. are economically important bacterial diseases affecting a wide range of crops worldwide. In 2024, root gall symptoms were observed on greenhouse-grown Korean zucchini (Cucurbita moschata) in Cheongju, Korea. Seven bacterial isolates were obtained from galled roots and subjected to cultural, morphological, pathogenicity, and molecular analyses. All isolates produced characteristic pink colonies on 1A selective medium and were rod-shaped with multiple flagella, as observed by transmission electron microscopy. Pathogenicity was confirmed through inoculation of zucchini seedlings and carrot disk assays, in which typical gall symptoms developed. Multilocus sequence analysis based on four housekeeping genes (atpD, dnaK, glnA, and rpoB) revealed that all isolates clustered within the A. tumefaciens clade. These results demonstrate that A. tumefaciens is the causal agent of root gall disease in Korean zucchini. To our knowledge, this is the first comprehensive report of root gall disease caused by A. tumefaciens on Korean zucchini in Korea.
This study investigated the spatiotemporal dynamics of plant disease occurrence in horticultural crops in Cheorwon, Gangwon Province, Korea, in 2025. A total of 137 samples were collected from 76 farms across six regions and analyzed using polymerase chain reaction (PCR) and reverse transcription-PCR to detect seven fungal, three bacterial, and seven viral pathogens. Plant pathogens were detected in 47.4% of the surveyed farms, with bacterial diseases showing the highest detection rate (23.7%), followed by viral (15.8%) and fungal diseases (14.5%). Among fungal pathogens, Botrytis cinerea was the most prevalent species, accounting for 47.6% of detections, indicating a clear shift from the dominance of Phytophthora infestans and Pythium ultimum observed in 2025. In bacterial diseases, Ralstonia solanacearum was the predominant pathogen (76.0%), exhibiting a strong association with specific regions and crops, particularly tomato and paprika. For viral diseases, tomato spotted wilt virus accounted for 88.2% of detections and showed a tendency toward spatial localization in specific areas. The disease occurrence period extended from March to October, which is longer than that observed in the previous year. This extension may be associated with prolonged high humidity conditions resulting from increased rainfall during the late growing season. Additionally, co-infections involving fungal, bacterial, and viral pathogens were identified in 19.4% of farms with detected pathogens, indicating increased complexity in disease management. Overall, this study reveals shifts in dominant pathogens, spatial localization of major diseases, and an extended disease occurrence period in Cheorwon. These findings provide fundamental data for developing region-specific disease management strategies under changing climatic conditions.
Anthracnose symptoms were observed on lemon balm (Melissa officinalis) plants growing in fields at locations Cheongju and Okcheon, Korea, during investigation of the crop disease occurrence in August 2024. The symptoms initially appeared as small, circular or irregular dark brown to black spots on the leaves, petioles, and stems. In the later stages, the symptoms expanded to irregular spots on the plants, and severely diseased plants blighted and died. The disease incidence on the plants in the fields ranged from 20% to 40%. Four single-conidium isolates obtained from the diseased plants were found to belong to Colletotrichum sp. based on their morphological characteristics. The Colletotrichum sp. isolates were tested for their pathogenicity on lemon balm leaves through artificial inoculation. Among the four isolates tested, three induced lesions on lemon balm leaves by artificial inoculation, but one did not. The lesions on the leaves induced by the inoculation tests with the three isolates were similar to those observed in the investigated fields. Two out of the pathogenic isolates were identified as Colletotrichum gigasporum, and one as Colletotrichum truncatum based on phylogenetic analyses and morphological characteristics. This is the first report of C. gigasporum and C. truncatum causing anthracnose in lemon balm in Korea.
Plant-parasitic nematodes (PPNs) are an important constraint in turfgrass production. This study was conducted to survey the species and densities of PPNs on Korean golf courses and to identify those exceeding threshold damage levels that require management. Seventeen species of PPNs belonging to seven families and 11 genera were identified. Mesocriconema nebraskense was the most prevalent, followed by Helicotylenchus microlobus, Tylenchorhynchus claytoni, and Paralongidorus koreanensis. Overall, the detection rate of nematodes exceeding the damage threshold was highest for P. koreanensis. However, this varied by turfgrass species: T. claytoni was highest on bentgrass, P. koreanensis on zoysiagrass, and H. microlobus on Kentucky bluegrass. Therefore, it is necessary to implement control strategies based on accurate identification and density of damaging nematodes, tailored to specific turfgrass species.
A phytoplasma associated with poinsettia has previously been reported in Korea, but the report primarily focused on stem flattening symptoms and was based solely on partial 16S ribosomal RNA (rRNA) gene sequence analysis. In this study, phytoplasma-infected poinsettias collected in Jinan and Jeonju, Korea were examined for diverse symptom expression and additional molecular characterization of the associated phytoplasma. All seven plants showed a free-branching phenotype. Symptom severity ranged from low free-branching, with larger leaves and long internodes, to severe free-branching, with shortened internodes and small, irregularly twisted leaves. Based on 16S rRNA gene sequence and iPhyClassifier analyses, the phytoplasma detected in this study was assigned to subgroup 16SrIII-A of the X-disease phytoplasma group (16SrIII). Although this assignment differs from the previous Korean report, which classified poinsettia-associated phytoplasmas subgroup 16SrIII-H, the present study interpreted the classification using an updated 16SrIII subgroup framework. Sequence analyses of more variable regions, including the 16S-23S intergenic spacer region, ribosomal protein (rp) operon, and secA gene, showed 99.46-99.55% nucleotide identity with ‘Candidatus Phytoplasma pruni’-related reference strains. Phylogenetic analyses showed that the poinsettia-associated phytoplasmas in Korea were closely related to the subgroup 16SrIII-A. These results expand the known symptom spectrum of phytoplasma-infected poinsettias and provide multilocus molecular characterization supporting the phylogenetic placement of poinsettia-associated phytoplasmas in Korea.
This study was conducted to identify the major pathogens causing branch dieback symptoms in landscape trees in residential areas and to evaluate their biological characteristics and fungicide sensitivity. Fungal isolates were obtained from nine tree species in Cheongju of Chungbuk. Multi-gene phylogenetic analysis using internal transcribed spacer, translation elongation factor 1-α, and β-tubulin identified the pathogens as Diaporthe eres, Botryosphaeria dothidea, Neopestalotiopsis clavispora, and Pestalotiopsis trachycarpicola. D. eres showed high isolation frequency across various hosts, while B. dothidea exhibited the strongest pathogenicity in virulence tests. Mycelial growth of N. clavispora and P. trachycarpicola was significantly inhibited at 30°C. Among 16 fungicides tested, benzimidazoles, fluazinam and DMIs (De-methylation Inhibitors) fungicides showed high inhibitory effects against all major pathogens. These results provide fundamental data for the accurate diagnosis and effective management of branch dieback in residential landscape trees.
Garlic white rot caused by Stromatinia cepivora was surveyed in major garlic-producing areas of Goheung, Jeonnam, Korea, from May 18 to 20, 2026. A total of 30 garlic fields in eight regions were investigated. The disease was detected in 18 fields, corresponding to a field incidence of 60.0%. Disease incidence within fields ranged from 0% to 41%, with an average incidence of 7.5%. Pungyang-myeon showed the highest average disease incidence (19.4%), and fields with a previous history of the disease exhibited higher incidence (13.2%) than those without disease history (3.1%). Typical symptoms and black sclerotia were observed on infected plants, and the pathogen was confirmed through isolation from collected sclerotia. These results indicate that garlic white rot occurred widely in major garlic-producing areas of Goheung in 2026 and highlight the need for continuous monitoring and integrated disease management.
Rice sheath blight caused by Rhizoctonia solani AG-1 IA is a major disease of rice. In this study, a simple seedling inoculation method using small nursery trays was developed for pathogenicity assays and resistance screening. Rice seedlings at the 4-5 leaf stage were inoculated with 5-mm-diameter mycelial plugs and incubated at 30°C under humid conditions for 10 days. Disease severity was assessed using relative lesion height (RLH) and the IRRI Standard Evaluation System. Typical sheath blight symptoms developed consistently, and reproducible disease reactions were obtained across 12 rice cultivars in three independent experiments. This method requires minimal space and inoculum preparation, providing a rapid and reproducible system for rice sheath blight research.
Persimmon anthracnose is a major disease affecting fruit quality and yield in persimmon-growing regions, yet information on the species diversity of causal pathogens in Korea remains limited. This study aimed to identify Colletotrichum species associated with anthracnose symptoms on persimmon fruits and to evaluate their pathogenicity. Sixteen fungal isolates were obtained from symptomatic fruits collected pear research center in Naju, Korea, and their morphological characteristics—colony features, conidial morphology, and appressoria— were examined. Multilocus sequence analysis using internal transcribed spacer, actin, β-tubulin, glyceraldehyde-3-phosphate dehydrogenase, chitin synthase I, calmodulin, the intergenic spacer region between Apn2 and Mat1-2-1 (ApMat) was performed to determine species identity and phylogenetic relationships. Phylogenetic analysis revealed that most isolates (87.5%) belonged to Colletotrichum horii. One isolate each of C. siamense and C. fructicola were also identified; notably, C. fructicola represents the first report of this species on persimmon in Korea. Pathogenicity tests showed that all three species induced typical sunken lesions on wounded fruits, and the inoculated pathogens were successfully re-isolated, fulfilling Koch’s postulates. These findings demonstrate that persimmon anthracnose in Korea is caused by multiple Colletotrichum species with clear genetic differentiation. The detection of C. fructicola suggests that the species spectrum of anthracnose pathogens may be broader than previously recognized. This study provides essential baseline information for disease diagnosis, epidemiological monitoring, and the development of resistant cultivars in future breeding programs.
Anthracnose symptoms were found on fruit of papaya trees (Carica papaya) cultivated in greenhouses in Taean and Gokseong, Korea, during surveys of crop diseases in 2020 and 2021. The initial symptoms on the fruit appeared as small, water-soaked, slightly depressed, circular or oval brown spots. As the disease progressed, the symptoms turned sunken, dark brown to black, and enlarged. In the later stages, yellowish conidial masses formed on the lesions. The disease symptoms on the fruit occurred up to 5% in the investigated greenhouses. Seven single-conidium isolates were obtained from the diseased fruit and found to correspond to Colletotrichum sp. based on their morphological characteristics. Two out of the seven isolates were identified as Colletotrichum aenigma, and the others as Colletotrichum fructicola by analysis of phylogenetic characteristics. The isolates of C. aenigma and C. fructicola were tested for their pathogenicity on papaya fruit using artificial inoculation. Both the Colletotrichum spp. isolates induced anthracnose symptoms in papaya fruit, similar to those observed in the investigated greenhouses. This is the first report of C. aenigma and C. fructicola causing papaya anthracnose in Korea.
In June 2025, celery (Apium graveolens) plants showing wilting and crown rot were collected from commercial fields in Taebaek, Korea. Six oomycete isolates were recovered from symptomatic roots, crowns, and stalks. Based on morphological and cultural characteristics, together with sequence analyses of the internal transcribed spacer (ITS) and cytochrome c oxidase subunit I (cox1) regions, the isolates were identified as Phytophthora tentaculata. Temperature-dependent growth assays on V8 agar (V8A) revealed that all isolates exhibited optimal mycelial growth at 20-25°C, with minimum and maximum growth temperatures of 10°C and 30°C, respectively. Sporangium production varied markedly among culture media and was highest on water agar, followed by 5% V8A, whereas higher V8 concentrations strongly suppressed sporulation. Pathogenicity tests conducted using mycelial plug inoculation resulted in stalk rot, wilting, and plant collapse on celery, consistent with field symptoms. The pathogen was successfully reisolated from symptomatic tissues, whereas no Phytophthora species were recovered from mock-inoculated controls, thereby fulfilling Koch's postulates. This study represents the first integrated biological and pathological characterization of P. tentaculata associated with celery blight in Korea and provides essential information for accurate diagnosis and improved disease management.
The FBcastS automated system determines optimal control timing for fire blight blossom infection by running the K-Maryblyt model with observed weather data and short-term forecasts for today, tomorrow, and the day after tomorrow, and issuing recommendations based on blossom infection risk (BIR). From 2022 to 2024, BIR during the entire flowering period was analyzed at the Chungju site using observed and forecast data. The first control recommendation dates at Chungju were April 23 in 2022, April 19 in 2023, and April 15 in 2024. Except in 2024, first recommendation dates at 31 major apple-producing and fire blight-affected sites in Korea were the same as or within 2 days of those at Chungju. Confusion matrix analyses were conducted for the entire flowering period across the 31 sites and for the two in-bloom spray dates recommended by the Rural Development Administration (RDA), and agreement with spray dates derived from observed weather was evaluated using recall (sensitivity). Recall values by RDA recommendations using today's and tomorrow's forecasts in 2022 and 2024 were 0.74-0.92, whereas recall using the day-after-tomorrow forecast in 2022 and 2024 were 0.18-0.49. These results indicate that control recommendations based on today's and tomorrow's forecasts are reliable, while those based on longer lead-time forecasts require caution. Among the 3 years, 2023 showed both the lowest infection risk and the lowest recall. Improved understanding of K-Maryblyt and FBcastS supports sustainable integrated disease management, including monitoring epiphytic infection potential (EIP) on stigmas and determining copper spray timing based on bud break predictions.
Various plant parasites cause damage to turfgrass, and various parasitic nematodes also cause damage to zoysiagrass, particularly the ectoparasitic nematodes. Turfgrass damage caused by various ectoparasitic nematodes is prevalent on golf courses, and nematode management is urgently needed, but information on practical nematicides is scarce. Therefore, this study compared the control efficacy of novel nematicides (Imicyafos, Fluopyram, and Cyclobutrifluram) against ectoparasitic nematodes that are problematic in zoysiagrass, based on formulation and soil depth. The control efficacy of nematicides on golf course turfgrass, which exhibited differences in nematode species composition and density, varied depending on nematode group, formulation, and soil depth. Granular nematicides were relatively effective in test sites receiving high precipitation after treatment, and control efficacy was higher at depths of 0-5 cm near the soil surface than at depths of 5-10 cm. It is believed that the type and formulation of nematicides should be considered taking into account the soil distribution characteristics of the dominant nematodes in the control target area.
White rot of Allium crops is a soil-borne disease in which sclerotia play a crucial role in pathogen survival and infection. This study aimed to re-identify the causal agent of white rot isolated from garlic and chives and to evaluate the effects of fungicides on mycelial growth, sclerotial formation, and sclerotial germination. Multilocus phylogenetic analysis based on internal transcribed spacer, β-tubulin, and glyceraldehyde 3-phosphate dehydrogenase sequences confirmed that all isolates belonged to Stromatinia cepivora. In fungicide sensitivity assays, most fungicides effectively inhibited mycelial growth, whereas pencycuron showed limited activity. Fludioxonil exhibited strong inhibitory effects on both sclerotial formation and germination, regardless of application method, and provided stable disease control in garlic clove dipping assays. These results suggest that fludioxonil is a promising fungicide for suppressing multiple developmental stages of S. cepivora and provide fundamental information for the effective management of white rot in Allium crops.
This study assessed the incidence and distribution of major viral infections in grapevines across South Korea. A total of 534 grapevine samples representing five cultivars were collected and tested for three economically important viruses: grapevine fleck virus (GFkV), grapevine leafroll-associated virus (GLRaV)-1, and GLRaV-3. The overall infection rate among all samples was 92.7%, indicating a high prevalence of viral infections in domestic vineyards. Individual virus detection rates were 88.8% for GFkV, 33.5% for GLRaV-1, and 31.6% for GLRaV-3. Regional infection rates varied, with 100% incidence observed in Daejeon and Gangwon-do, followed by Chungcheongbuk-do (99.4%), Chungcheongnam-do (95.2%), Jeollabuk-do (94.2%), Gyeongsangbuk-do (88.4%), Gyeongsangnam-do (87.5%), and Gyeonggi-do (77.0%). Among grapevine cultivars, infection frequencies were highest in Chungrang (100%), followed by Shine Muscat (95.5%), Muscat Bailey-A (90.5%), Campbell Early (90.1%), and Kyoho (84.6%). Single infections accounted for 44.8% of cases, double infections for 34.5%, and triple infections for 13.5%. The most prevalent double infections were GFkV + GLRaV-1 (19.5%) and GFkV + GLRaV-3 (14.8%), while co-infection with GLRaV-1 + GLRaV-3 occurred rarely (0.2%). The incidence of triple infections was highest in Shine Muscat (17.2%), followed by Campbell Early (11.7%), Kyoho (7.7%), and both Chungrang and Muscat Bailey-A (4.8%). Our findings highlight the widespread occurrence of grapevine viruses across regions and cultivars in Korea, underscoring the urgent need for effective management strategies to control virus diseases in grapevine.
Bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) is one of the most destructive diseases affecting kiwifruit production worldwide. In Korea, the composition of cultivated kiwifruit cultivars has changed substantially over the past two decades. This study examined whether long-term transitions in host cultivar composition were associated with changes in pathogen lineage prevalence. National records of cultivar acreage, pathogen surveillance data, and observations of cultivar-dependent disease expression were analyzed. When production was dominated by the hexaploid cultivar ‘Hayward’, bacterial canker outbreaks were sporadic and mainly associated with Psa biovar 2. Following the rapid expansion of yellow-fleshed Actinidia chinensis cultivars in the early 2000s, Psa biovar 3 increased markedly and eventually became the dominant lineage nationwide. Greenhouse inoculation assays and field observations further revealed cultivar-dependent differences in disease expression. These results suggest that host cultivar composition may influence pathogen population structure at the production-system scale.
Grapevine fleck virus (GFkV) is a graft-transmissible pathogen that threatens grapevine production in rootstocks and hybrid cultivars. Its early and accurate detection is essential for certifying virus-free planting materials. This study developed and validated a reverse-transcription droplet digital polymerase chain reaction (RT-ddPCR) assay for the specific and absolute quantification of GFkV in grapevine tissues. The assay demonstrated high specificity, showing no cross-reactivity with other major grapevine viruses. Meanwhile, RT-ddPCR exhibited approximately 10-fold higher sensitivity than RT-quantitative PCR (RT-qPCR), with a detection limit of 0.73 copies/μl. Both RT-ddPCR and RT-qPCR exhibited high linearity (R2=0.9997 and 0.9983, respectively). In field validation, GFkV was detected in 84.8% (56/66) of the samples via RT-ddPCR, whereas RT-qPCR detected the virus in 53.0% (35/66) of the samples. These results indicate that RT-ddPCR is a highly sensitive and reliable method for GFkV detection in grapevines.
Bacterial canker and bacterial leaf spot are among the most economically important diseases affecting kiwifruit production, and their management has relied heavily on antibiotics and copper-based bactericides. However, increasing concerns regarding antibiotic resistance and environmental impact have highlighted the need for alternative disease control strategies. In this study, the antibacterial activity and disease control efficacy of silver-stabilized hydrogen peroxide were evaluated against major bacterial diseases of kiwifruit under laboratory, greenhouse, and orchard conditions. Silver-stabilized hydrogen peroxide significantly inhibited the growth of Pseudomonas syringae pv. actinidiae and Acidovorax valerianellae in vitro, including streptomycin-resistant isolates. Under greenhouse conditions, application of the oxidative agent reduced disease severity by approximately 40-60%, while disease suppression of approximately 30-50% was observed under orchard conditions, depending on disease type and assessment timing. These ranges reflect variability among experimental replicates and environmental conditions, while treatment effects remained statistically significant. Although disease control efficacy was generally slightly lower than that achieved with conventional antibiotic treatments, silver-stabilized hydrogen peroxide consistently suppressed disease development under both controlled and field conditions. These results indicate that silver-stabilized hydrogen peroxide provides stable and reproducible disease suppression and may serve as a reliable complementary component of integrated disease management programs aimed at reducing antibiotic dependence in kiwifruit production systems.
Hydrogen peroxide (H2O2) and sodium nitroprusside (SNP) have shown different in vitro antimicrobial activities against strawberry pathogens Colletotrichum fructicola, Phytophthora cactorum and Neopestalotiopsis clavispora. The antimicrobial activities were evaluated by measuring colony diameters on half-strength potato dextrose agar supplemented with different H2O2 and/or SNP concentrations at 20°C, 25°C, and 30°C. Mycelial growth of C. fructicola and P. cactorum decreased in the presence of H2O2 and SNP individually across all three temperatures, and the two compounds showed synergistic antimicrobial activities. N. clavispora growth was arrested by H2O2 at three temperatures, but the SNP-limited growth was only found at 30°C. Synergistic antifungal activity of H2O2 and SNP against N. clavispora was found at 30°C, but not at 20°C and 25°C. These results suggest that the antimicrobial efficacies of H2O2 and SNP against these strawberry pathogens are temperature-dependent and can be significantly enhanced by combining the two compounds.
During 2022-2023 growing season, 11 Iraqi provinces were surveyed for the prevalence of Potyvirus citrulli in cucurbit fields. Thirty-six symptomatic samples were screened using reverse transcription-polymerase chain reaction and three sets of potyviral specific primers targeting the partial helper component proteinase (HC-Pro), cylindrical inclusion (CI), and nuclear inclusion b protein (Nib) genes within P. citrulli genome. Twentynine out of 36 samples were infected with P. citrulli. Sequence comparisons of the three genomic regions revealed that 17 isolates shared 88-100% nucleotide identity with isolates from National Center for Biotechnology Information indicating they were genetically variable. Phylogenetic analyses confirmed the variation of HC-Pro, CI, and NIb separating the 17 isolates within P. citrulli group. The high nucleotide sequence identity to existing isolates suggests successful introduction enabling to overcome and adaptation of those isolates to the Iraqi environment. Inoculation tests revealed variable symptoms, when zucchini plants exhibited the most severe symptoms compared to watermelon and cucumber plants. These findings highlight that P. citrulli can be a serious threat to cucurbit cultivation in Iraq.
