Codonopsis javanica, a Campanulaceae herb endemic to Guizhou, is locally called "Tudangshen", its root is used in medicine to fortify spleen-qi, moisten the lung and arrest cough, and promote lactation. In June 2023, root rot of C. javanica was observed in a cultivation field in Xiuwen County (106°46'48" E, 26°53'59" N), Guizhou Province, with the estimated disease incidence ranging from 20% to 50%. The initial symptoms were light brown spots on the surface of the root, and the spots were brown or black in severe cases, and the lower end of the root and the rhizome were rotted. The aboveground portions of the leaves exhibited yellowing and wilting, followed by withering and death. The diseased root tissue (5 mm × 5 mm) was cut and disinfected with 75 % alcohol for 15 s, 5 % sodium hypochlorite treatment for 1 min, followed by three rinses with sterile distilled water. After drying, the samples were transferred onto Potato Dextrose Agar (PDA) and incubated at 28 °C in darkness for 3-5 days. Through hyphal tip culture methodology (Senanayake et al. 2020), 12 strains with similar morphology were obtained. The colonies were white to purplish red. The fungus produced two types of conidia: microconidia and macroconidia. The microconidia were ovate, without septa or 1-2 septa, and the size was 4.98-9.22 × 1.88-3.65 μm. The macroconidia were sickle-shaped, slightly curved, 1-4 septa, and the size was 21.55-37.92 × 3.10-6.50 μm. Chlamydospores were subspherical to spherical. Based on these morphological features, the isolates were suspected to be Fusarium oxysporum (Leslie et al. 2006). For molecular confirmation of the morphological identification, strain ZPJ1 was randomly selected as a representative isolate for DNA extraction. The primers ITS1/ITS4, EF1-F6/R6, and RPB2-5F/RPB2-7cR were used to amplify three genomic DNA regions including the internal transcribed spacer (ITS)(Crous et al. 2021), translation elongation factor 1-alpha (EF1)(Moslemi et al. 2017), and RNA polymerase II second largest subunit (RPB2)(Xiang et al. 2025). The sequences of ZPJ1 (accession numbers PV750775, PV759349, and PV759350 for ITS, EF1 and RPB2, respectively) were deposited in GenBank, demonstrating a sequence homology of 99 % to 100 % (546/546, 702/705, 974/978) with F. oxysporum (accession numbers PP596264, MN892354, MN457466). Based on morphological features and maximum likelihood method analyses of combined ITS, EF1, and RPB2 gene sequences, strain ZPJ1 was identified as F. oxysporum. Pathogenicity experiments were conducted in a greenhouse with a temperature ranging from 24 to 27 °C and a relative humidity of 80 %. Root wounding was performed on potted C. javanica seedlings (n = 5, 1-year-old) using a sterile needle. A spore suspension (150 mL, 1 × 106 conidia/mL) of strain ZPJ1 was inoculated onto the wounds, with an equal volume of sterile water used as the control. After 18 days, all inoculated plants developed characteristic root rot symptoms, while the plants in the control group remained healthy and did not show any symptoms of root rot disease. F. oxysporum was successfully reisolated from the symptomatic roots and identified by the morphology and the molecular methods de-scribed above, meeting Koch’s postulates. Based on current understanding, this is the first report of F. oxysporum causing root rot in C. javanica in China. These findings provide a basis for the early detection of C. javanica root rot caused by F. oxysporum and the formulation of targeted control measures.
Zhang et al. (Sat,) studied this question.