2026/07/28 by Weiran Chen, Cunyan Li, Qingfang Meng +2
paper · doi:10.1094/pdis-05-26-0965-pdn
Capsella bursa-pastoris is a herbaceous plant from the family Brassicaceae, with medicinal and edible value (Łukaszyk et al. 2024). In recent years, downy mildew on C. bursa-pastoris has consistently occurred in early spring, from early March to late April in the campus fields of Hebei Agricultural University in Baoding, China. Initially, small pale spots appear on the adaxial leaf surface. Under high humidity, white downy mildew develops on the abaxial surface. Sometimes the disease progresses, the white downy mildew also appears on the adaxial leaf surface, stems, and flower stalks. Finally, infected stalks become swollen and bent, and the plant dies. Sporangiophores (n = 120) were colorless, slightly swollen at the base, with a total length of 158.39 to 469.21 µm, dichotomously branched 2 to 7 times, and their apical branches were slender, sharp or curved. Sporangia (n = 120) were ellipsoid to ovoid, hyaline, and borne at the ends of sporangiophore branches, measuring 21.04–30.90 (average 25.97) × 17.18–26.86 (average 22.72) μm, with a length/width ratio from 0.78 to 1.80 (average 1.29). Oospores (n = 120) were spherical, yellowish-brown, and measured 29.50–40.52 (average 35.01) μm in diameter. The pathogen (designated WY) was identified as Hyaloperonospora parasitica according to the morphological similarity to H. parasitica on Cardamine violifolia (Li et al. 2025). For molecular confirmation, partial sequences of the internal transcribed spacer (ITS) (White et al. 1990), the Cytochrome c oxidase subunit II (COX2) (Choi et al. 2015) and the large subunit (LSU) (primers LROR, Moncalvo et al. 1995; LR6-O, Riethmuller et al. 2002) of this isolate were amplified by PCR. BLASTn analysis revealed that the obtained ITS, COX2 and LSU sequences (accession numbers: PZ277000, PZ276707 and PZ344554) shared 99.46%, 99.34% and 95.49% identity with those of H. parasitica (MF784706.1, DQ365710.1 and EU054889.1) in the NCBI database. Pathogenicity was tested by spraying a spora suspension onto 10 healthy leaves, with control leaves (n = 10) treated with sterile water, in the field at Hebei Agricultural University. After 10 days, only inoculated leaves developed typical downy mildew symptoms, and the PCR amplicon sequence using primers ITS1/ITS4 was identical to that of the original inoculum, fulfilling Koch’s postulates. To our knowledge, this is the first report of downy mildew caused by H. parasitica on C. bursa-pastoris in China. This finding extends the known host range and geographic distribution of H. parasitica.