This is the first report of G. irregulare infecting common sage, and recognizing G. irregulare as a pathogen of common sage is important for effective disease management and reducing losses in the greenhouse.
Abstract
In February 2024, common sage plants (Salvia officinalis) in a commercial greenhouse in Randolph County, North Carolina were submitted to the NC State University Plant Disease and Insect Clinic. Sage plants in multiple trays were observed to have symptoms of wilting, chlorosis, and root rot. Plants had necrotic roots and necrotic areas on leaves, and eventually entire plants collapsed. Symptomatic root segments were rinsed in sterile deionized water, blotted dry, and placed on CMA-PPP selective medium (Eckert and Tsao 1962). Three isolates, each from a different symptomatic plant, were transferred to acidified potato dextrose agar. The morphological structures from each isolate matched the description of Globisporangium irregulare (formally Pythium irregulare) reported by van der Plaats-Niterink (1981). DNA samples were extracted from mycelium mats of the three isolates using the DNeasy Plant Mini Kit (Qiagen, Germantown, MD). The cytochrome oxidase subunits I and II (COI and COII) (Martin 2000; Robideau et al. 2011) and internal transcribed spacer (ITS) regions 1 and 4 (White et al. 1990) were amplified. The amplicons were sequenced and analyzed by BLASTn in NCBI GenBank. The isolates were confirmed to be Globisporangium irregulare with ≥98% identity match and 100% query coverage to type isolate sequences with the following accession numbers HQ708678, GU071760, and HQ643595 for COI, COII, and ITS, respectively. Isolates from this study were deposited in GenBank under accession numbers PP965484–PP965486, PP965487–PP965489, and PP965682–PP965684. To complete Koch’s postulates, ten 14-day-old sage plants were inoculated with 20 mL of 1 × 10
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oospores/mL of G. irregulare (isolate NC_65624), following a modified protocol (McGehee and Raudales 2021). Individual plants were grown in 5.7 × 5.7 × 6-cm cells cut from six-cell tray inserts filled with a soilless peat-perlite substrate. Plants were maintained indoors on growth carts at 26°C, 50% relative humidity, and a 14-h photoperiod. Wilting occurred 5 days after inoculation, and 60%–70% of inoculated plants showed reduced growth, wilting, and root rot after 14 days. Ten non-inoculated control plants remained symptomless. G. irregulare was recovered from symptomatic roots from all inoculated plants using the method mentioned previously. The experiment was conducted twice. To my knowledge, this is the first report of G. irregulare infecting common sage. G. irregulare has been reported on other herbs such as cilantro (Infante et al. 2018) and clary sage (Reeves et al. 2021). Recognizing G. irregulare as a pathogen of common sage is important for effective disease management and reducing losses in the greenhouse. Preventing root rot caused by oomycetes in greenhouse production systems requires consistent sanitation protocols, avoidance of over-fertilization and over-irrigation, and responsible use of fungicides to minimize disease risk.
To the authors' knowledge, this is the first report of P. ramorum occurring on C. siliqua globally and the first confirmation of Koch’s postulates for this host-pathogen combination.
Dinh-Hieu Pham, T. Pastalka, Huiying Liu et al.· Plant Disease· 0 citations
Snap bean (Phaseolus vulgaris L.) is an important crop in Sinaloa, Mexico where 2,076 ha were cultivated in 2024, representing 21.88% of the national production area (DGSIAP 2026). In December 2024, root rot was observed in ~ 40% 4‑month‑old P. vulgaris plants grown in a 5‑ha outdoor commercial field in Culiacán, Sinaloa (24°14'44.7"N 107°10'59.6"W). Plants also exhibited crown rot, stunted growth, wilting, leaf yellowing, and partial foliage necrosis and defoliation, and plant death. Thirty pieces (1‑cm²) of rotted tissue were collected from the roots of 15 randomly selected diseased plants. The fragments were surface‑sterilized in 1% NaClO, rinsed in sterile distilled water and dried on paper. Five pieces were placed equidistantly per Petri dish containing PDA supplemented with streptomycin sulfate (0.3 g L⁻¹) and incubated at 30 °C for 5 days. Out of the 6 isolates generated, 3 were selected for identification. The isolates were plated on V8 medium (800 mL distilled water, 200 mL V8 juice, 2 g CaCO₃, and 15 g agar) and incubated for 7 days at 30 °C. Cultures developed white, dense, cottony, aerial, and well‑branched mycelia; the hyphae were hyaline and coenocytic, and the sporangia were filamentous, lobulate, and irregular in shape. These traits were consistent with Pythium aphanidermatum (Watanabe 2002; Castro-Diego et al. 2025). PCR analysis was performed with the internal transcribed spacers ITS1 and ITS4 (White et al. 1990) and the cytochrome oxidase c subunit 1 (COI) (Robideau et al. 2011). The sequences were deposited in GenBank under PX671483, PX671484, and PX671485 for ITS, PX677389, PX677390, and PX677391 for COI, corresponding to isolates PYTHFRI3CULSIN, PYTHFRI1CULSIN, and PYTHFRI8CULSIN, respectively. BLAST analysis showed that PX671483, PX671484, and PX671485 shared 100% identity with P. aphanidermatum sequence HQ643439 (555/555 bp, 664/664 bp, and 739/739 bp, respectively), and that PX677389, PX677390, and PX677391 also exhibited 100% identity with sequence HQ708486 (596/596 bp, 628/628 bp, and 626/626 bp, respectively) (Robideau et al. 2011). Phylogenetic analyses using the Neighbor‑Joining method with COI sequences and 1,000 bootstrap replications in MEGA 11 placed the three isolates within the P. aphanidermatum clade. To verify the pathogenicity of the isolates, 2 pathogenicity assays were conducted. In each assay, 10 P. vulgaris seedlings were individually inoculated at the stem base with 5 mL of inoculum (0.25 g of macerated mycelium in 100 mL of sterile water) 15 days after emergence. An additional 10 seedlings were inoculated with sterile water to serve as controls. All plants were maintained in a growth chamber at 28 ± 2 °C, 70 ± 5% RH, and a 12:12 h photoperiod for 30 days. Inoculated plants developed symptoms similar to those observed in the field, whereas control plants remained asymptomatic. Pythium aphanidermatum was successfully reisolated and identified from symptomatic root tissues, fulfilling Koch’s postulates, while no isolates were obtained from control plants. Although P. aphanidermatum was previously reported on P. vulgaris in Mexico (McGuire and Crandall 1967), details on methodology and isolation site were not provided. This study represents the first confirmed occurrence of P. aphanidermatum causing root rot in P. vulgaris in Mexico supported by both morphological and molecular evidence and the first documented case in the state of Sinaloa.
Oscar Alejandro Sánchez-Gómez, Juan Antonio Castro-Diego, W. Rubio-Aragón et al.· Plant Disease· 0 citations
In September 2025, a total of 15 soybean fields were surveyed in Muan and Gongju, Korea. Irregular leaf blight symptoms were observed in five fields, with approximately 1–10% of soybean plants showing symptoms in each affected field. To isolate the causal pathogen, symptomatic leaf tissue was surface-disinfected with 1% NaOCl for 1 min, rinsed with sterile distilled water, and placed on potato dextrose agar (PDA). The plates were incubated at 20℃ for 7 days, and olive-brown hyphae growing from the tissues were subcultured twice on PDA. Five isolates with similar morphology were obtained from symptomatic leaves, and one representative isolate, DA17-37, was selected for further morphological, molecular, and pathogenicity analyses. The conidia were predominantly oval to ellipsoidal and aseptate, measuring 3.71-6.45 x 1.77-2.83 μm, with a mean size of 5.11 x 2.14 μm (n=30). The ascospores were mostly oval and 1-septate, measuring 12.49-18.25 x 4.13-5.41 μm with a mean size of 15.08 x 4.48 μm (n=30). Additionally, multicellular chlamydospores were observed. Overall, these morphological characteristics were consistent with those of the genus Didymella. To genetically characterize isolate DA17-37, genomic DNA was extracted, and the internal transcribed spacer (ITS), beta-tubulin (tub2), and RNA polymerase II second largest subunit (rpb2) genes were amplified by PCR using the respective primer sets described previously (Gorny et al. 2016; Liu et al. 1999; Woudenberg et al. 2009). The resulting sequences were deposited in GenBank under accession numbers PZ274701, PZ433240, and PZ439292. Maximum likelihood phylogenetic analysis of the concatenated dataset showed that isolate DA17-37 clustered with the reference strains of Didymella americana. To confirm the pathogenicity of isolate DA17-37, a conidial suspension (1 x 10
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conidia/mL) prepared from 30-day-old PDA cultures grown at 20℃ was sprayed onto 2-week-old potted soybean plants. Control plants were sprayed with sterile distilled water. The inoculated plants were incubated in a dew chamber at 26℃ for 3 days and then transferred to a growth chamber maintained at 26℃ and 70% relative humidity under a 16-h photoperiod. Symptoms first appeared at 7 days post-inoculation (dpi), and representative symptoms showing disease progression were photographed at 14 dpi, whereas the uninoculated control plants remained healthy. To satisfy Koch’s postulates, the same pathogen was re-isolated from symptomatic leaves and identified based on morphology and DNA sequence analysis. Didymella americana has been reported as a causal pathogen of leaf blight on lima bean in the United States. To the best of our knowledge, this is the first report of leaf blight caused by D. americana on soybean in Korea. Continued monitoring is needed to assess the potential spread of this disease in Korea and to support the development of appropriate disease management strategies.
S. Choi, Eun Young Kim, Shinhwa Kim et al.· Plant Disease· 0 citations
Atractylodes chinensis (DC.) Koidz is an important medicinal plant in China. In 2024, symptoms of root rot were observed in Hebei Province, China, with disease incidence ranging from 5 to 10% in surveyed fields. Affected plants initially displayed wilting, leaf curling, and gradual brittleness of foliar tissue. Root tissues turned brown and soft, gradually shrinking and hardening, becoming easily breakable and ultimately leading to plant death. To identify the pathogen, small sections were excised from the margins between symptomatic and healthy tissues, surface-sterilized in 75% ethanol for 30 s followed by 0.1% HgCl2 for 1 min, and rinsed three times with sterile distilled water. A fungus was isolated and subcultured on PDA at 25°C in the dark for 5-7 days, colonies exhibited white aerial mycelia with subsurface beige pigmentation. Macroconidia were falcate, typically 5 to 7 septate, with a slight curvature in the midregion, measuring 30.8 to 52 × 4.8 to 6.5 µm (n = 50). Microconidia were oval to reniform and aseptate or with 1 to 2 occasionally 2 septa, measuring 8.9 to 15.2 × 2.8 to 3.5 µm (n = 50). Chlamydospores were abundantly produced within 2-4 weeks on carnation leaf agar (CLA) and the diameter were 5.4 to 8.6 (n = 50). These morphological characteristics were consistent with descriptions of species within the Fusarium solani species complex (Leslie and Summerell 2006). For molecular identification, partial sequences of the translation elongation factor 1-alpha (TEF) and RNA polymerase II second largest subunit (RPB2) genes were amplified using primers EF1/EF2 and RPB2-5F/7cR, respectively, following O'Donnell et al. (2022). Sequences were deposited in GenBank as TEF (PX549679) and RPB2 (PX549683). The obtained TEF (PX549679) and RPB2 (PX549683) sequences showed >99% identity and ≥99% query coverage with reference sequences of Fusarium solani (TEF, PQ862924; and RPB2, MT305173). A phylogenetic tree was constructed using concatenated TEF and RPB2 sequences in MEGA version 11.0.10 (Tamura et al. 2021) with the GTR+G model and 1,000 bootstrap replicates. Maximum Likelihood analysis placed the isolates within the F. solani clade with 99% bootstrap support. Pathogenicity of the representative isolate was confirmed on healthy 1-year-old A. chinensis plants (cultivar: Zhongqin 1). Roots were wounded with a sterile syringe needle (three wounds per root) and inoculated with 10 mL of a conidial suspension (1 × 106 conidia mL-1). Inoculated plants were maintained in a humid chamber at 25 ± 1°C and approximately 85% relative humidity. Control plants were treated with sterile double-distilled water. After 10 days, inoculated plants developed symptoms identical to those observed in the field, and the fungus was consistently reisolated from symptomatic tissues, thus fulfilling Koch's postulates. The experiment was conducted three times, each with 30 plants. Based on symptomatology, morphological characteristics, TEF and RPB2 sequence analysis, and pathogenicity tests, the pathogen was identified as F. solani. F. solani has previously been reported as a pathogen of Astragalus membranaceus var. mongholicus and Gastrodia elata in China (Xu et al. 2024; Chen et al. 2023). To our knowledge, this is the first report of F. solani causing root rot of A. chinensis in China. These findings provide important information on the causal agent of A. chinensis root rot and will support the development of disease management strategies and guide future research.
Qian Liu, Kaili Zhang, Yule Yao et al.· Plant Disease· 0 citations
To determine the species, the four isolates were molecularly identified by amplifying and sequencing the internal transcribed spacer (ITS) region and the translation elongation factor 1‑α (EF‑1α) using primers ITS1/ITS4 and EF1‑728F/EF1‑986R, respectively (White et al. 1990).
Juan Antonio Castro-Diego, Verónica Delgado-Pacheco, N. Ley-López et al.· Plant Disease· 0 citations
In August 2022 and September 2024, sugar beet (Beta vulgaris L.) leaves with several moderately large, light tan to brown, oblong to irregular leaf spots were collected from fields in Pembina, Grand Forks, and Walsh counties in North Dakota. Leaf spots bordered by 1-2 mm healthy tissue were excised and incubated in humidity chambers for 48 h under fluorescent and UV-A light with a 12-h light/dark cycle at 21 ± 1°C. Stemphylium-like conidia suspensions were collected into 0.01% Tween 20 by gentle pipetting, and 120 µl of suspension was spread onto thin water agar amended with ampicillin (200 mg/liter). After 24 h, individual germinating conidia were transferred to clarified V8 agar amended with ampicillin. Two isolates were collected in 2022, and thirteen isolates were collected in 2024. All cultures produced dark, solitary, multiseptate conidia that were round to oblong, approximately 35 × 17 µm, and formed in irregular clusters, consistent with descriptions of Stemphylium vesicarium (Metheny et al. 2022; Khan et al. 2023) and S. beticola (Hanse et al. 2015; Woudenberg et al. 2017). Genomic DNA was extracted from fifteen isolates using the method described in Lien and Chanda (2026). The internal transcribed spacer region of rDNA was amplified with primers ITS1F/ITS4 (Gardes and Bruns 1993; White et al. 1990), calmodulin (cmdA) with CALDF1/CALDR1, and plasma membrane ATPase with ATPDF1/ATPDR1 (Lawrence et al. 2013) and sent for Sanger sequencing at MCLAB (San Francisco, CA). Sequences were submitted to GenBank (ITS: PZ290169; cmdA: PZ301221; ATPase: PZ301222), and BLASTn searches showed 100% identity with MH879836.1 for ITS (577/577 bp) and MK675696.1 for cmdA (699/699 bp), and 99.7% identity with JQ671770.1 for ATPase (1230/1234 bp), supporting identification as S. vesicarium. Sequence similarity to the S. beticola type-strain CBS 141024 was 98.3% for ITS (519/528 bp) and 90.5% for cmdA (632/698 bp). Pathogenicity tests were conducted on 8-10 leaf stage sugar beet germplasm line USDA F1042 using two 2024 isolates. Pure cultures were grown on CV8 for 7 days under fluorescent and UV-A light with a 12-h light/dark cycle, and conidia were collected in 0.2% malt extract solution (Stammler et al. 2014). Three leaves were marked on each plant, and one half of each marked leaf was lightly abraded with autoclaved fine white Ottawa sand to induce injury prior to inoculation. For each isolate, three plants were sprayed with 10 ml of spore suspension (1 × 10
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conidia/ml). Three non-inoculated control plants were treated similarly and sprayed with 0.2% malt extract solution. Plants were moved to an environmental chamber maintained at >95% relative humidity and 20°C with a 14-h/10-h photoperiod for 7 days, then transferred to a greenhouse at 65 ± 10% relative humidity. The experiment was conducted twice. Leaf spot symptoms developed approximately 3 weeks after inoculation (WAI) on both injured and non-injured tissue (Supplementary Fig. S1) and were monitored until 5 WAI. No symptoms were observed on non-inoculated controls. Conidia, morphologically similar to the original isolates, were consistently reisolated after incubation of representative lesions in humidity chambers (Supplementary Fig. S2). These results expand the geographic distribution of S. vesicarium on sugar beet beyond Michigan and Minnesota. This study highlights the need for accurate diagnosis of leaf spot diseases and for developing effective disease management methods to minimize losses for growers.
A. K. Lien, James Allen Deleon, A. K. Chanda· Plant Disease· 0 citations
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