First Report of Epicoccum sorghinum Causing Leaf Blight on Pseudostellaria heterophylla in China

Abstract

Pseudostellaria heterophylla (Caryophyllaceae) is a perennial herb with tuberous roots. It is commonly cultivated as a medical plant for the pharmaceutical industry (Qin et al., 2025). In June 2024, serious leaf blight was observed on P. heterophylla in Tongren, Guizhou Province, China (28°10'40″N, 108°2'38″E). In a 0.33 ha field, the disease incidence was more than 70%. The lesions initially appeared as spots that later enlarged and coalesced into larger necrotic patches of blight. To identify the pathogen, 12 typical symptomatic P. heterophylla leaves were collected. Symptomatic leaf tissues (5 × 5 mm) were excised from infected margins, surface-sterilized sequentially with 75% ethanol (1 min) and 2% sodium hypochlorite (1 min), rinsed three times in sterile water, air-dried, and plated on potato dextrose agar (PDA; pH 7.0). Cultures were incubated at 25°C under dark conditions for 3 days. Nine isolates showed similar morphology on PDA with cottony aerial mycelia and pink concentric rings observed on the upper surface of the culture. Chlamydospores were identified, measuring 4.5 to 27.4 × 5.7 to 36.2 μm (n = 50). Conidia were unicellular, hyaline, oval, and measured 2.4 to 6.3 × 1.1 to 3.4 μm (n = 50). Morphological characteristics matched the description of Epicoccum sorghinum (Chen et al., 2017). DNA fragments were amplified using primers ITS1/ITS4 (White et al., 1990), TUB2Fd/TUB4Rd (Woudenberg et al., 2009), and LROR/LR5 (Vilgalys and Hester, 1990). Sanger sequencing was performed by Sangon Biotech (Shanghai, China), with sequences from strains SYDJ15, SYDJ16, and SYDJ19 deposited in GenBank (SYDJ15: PV133704, PV178136, and PV133774; SYDJ16: PV133736, PV178135, and PV133779; and SYDJ19: PV133741, PV178134, and PV133788). BLASTn analysis revealed >99% nucleotide identity between the ITS, TUB2, and LSU sequences of SYDJ15/16/19 and E. sorghinum (ITS (OR917791): 100%, 509/509 bp; 99.80%, 506/507 bp; 100%, 504/504 bp; TUB2: 99.72%, 362/363 bp, MN603100; 100%, 354/354 bp, KT783666; 99.12%, 450/454 bp, KT783666, and LSU (MK516207): 99.78%, 906/908 bp; 99.78%, 910/912 bp; 99.89%, 908/909 bp). Based on concatenated ITS, TUB2, and LSU sequences, the constructed phylogenetic tree confirmed that these isolates were E. sorghinum. To confirm pathogenicity, 1 mL of isolate SYDJ15 (10⁶ conidia/mL) was sprayed onto the leaves of three healthy 1-month-old P. heterophylla plants, and three control plants were sprayed with sterilized distilled water. The experiment was carried out in a greenhouse at 23±2℃ and 85% humidity. By 10 days post-inoculation, all inoculated leaves exhibited symptoms consistent with those observed in the field, whereas the controls were asymptomatic. The experiment was repeated three times with similar results. Based on morphological and molecular identifications, the fungus re-isolated from lesions was identified as E. sorghinum, thus completing Koch's postulates. The host range of E. sorghinum is broad and includes cereal crops, ornamental plants, and medicinal plants (Du et al., 2020; Zou et al., 2024), and it causes leaf blight disease that leads to considerable losses in agricultural production. To the best of our knowledge, our study represents the first report of E. sorghinum causing leaf blight on P. heterophylla in China. Further studies are warranted to prioritize the development of optimized control strategies for its sustainable management.

Keywords: Epicoccum sorghinum; Pseudostellaria heterophylla; leaf blight.