| Scientific Name | Hyaloperonospora brassicae (Gäum.) Göker, Voglmayr, Riethm., M. Weiss & Oberw., Can. J. Bot. 81:681 (2003) |
|---|---|
| Synonyms | 2 synonyms≡ Peronospora brassicae Gäum., Beih. Bot. Centralbl. 35:521 (1918)
≡ Peronospora parasitica subsp. brassicae (Gäum.) Maire, Mém. Soc. Sci. Nat. Maroc 45:14 (1937) |
| Disease | Downy mildew |
| Taxonomic Rank | |||
|---|---|---|---|
| Order | Peronosporales | Family | Peronosporaceae |
| Host Plant | |||
|---|---|---|---|
| Common Name | Rape, Oilseed rape (유채) | Scientific Name | Brassica napus |
| Common Name | Chinese cabbage (배추) | Scientific Name | Brassica rapa subsp. pekinensis |
| Common Name | (월동추) | Scientific Name | Brassica campestris var. nippo-oleifera |
| Common Name | Broccoli (브로콜리) | Scientific Name | Brassica oleracea |
| Common Name | Pak choi (청경채) | Scientific Name | Brassica rapa |
| Common Name | Tatsoi (다채) | Scientific Name | Brassica narinosa |
| Common Name | Chinese mustard (갓) | Scientific Name | Brassica juncea |
| Distribution | Australia, Austria, Czech Republic, Germany, Korea, Mexico, Myanmar, Portugal, Spain |
|---|---|
| Characteristics | Initial downy mildew symptoms on the pak choi appeared as yellowish to green-yellowish spots on the upper surface of leaves, while conidiophores and conidia occurred densely on the corresponding lower surface. Disease incidence ranged from 20 to 30%. Conidiophores (n=50) were hyaline, (210.0–)220.8–249.1–277.4(–300.0) µm in length, monopodially branched in 3-5 orders, while trunks were straight to slightly curved, 100-300 µm in length, with slightly swollen basal end of 8-15 µm wide. Ultimate branchlets (n=30) were mostly in pairs, curved to sigmoid, (9.5–)12.9–17.3–21.7(–26.7) µm long, (1.5–)2.1–2.7–3.4(–4.5) µm wide, with obtuse to subtruncate tips. Conidia (n= 30) were broadly subglobose, whitish, and measured (21.8–)23.4–25.7–28.0(–29.6) × (17.3–)19.2–21.4–23.7(–25.6) µm with a ratio of length to width of (0.98–)1.12–1.20–1.28(–1.36). |
| Notes | Downy mildew on Brassica crops was historically often attributed to Peronospora parasitica (= Hyaloperonospora parasitica) sensu lato. Molecular phylogenetic studies, however, support recognition of the Brassica-associated lineage as H. brassicae. Korean accessions from Chinese cabbage, broccoli, tatsoi, and pak choi have been confirmed as H. brassicae by molecular analyses. On pak choi, the Korean pathogen (KSNUH378) was identified using ITS and cox2 sequences and represented the first confirmed record of this disease in Korea (Lee et al. 2019). Downy mildew on pak choi has also been reported from China, Fiji, Japan, Malaysia, and Papua New Guinea, although many older overseas records have not been confirmed using modern molecular methods. Considerable genetic and pathogenic variation has also been reported among H. brassicae populations, including multiple phylogenetic groups in Australian Brassica crops. |
| Economic importance | Hyaloperonospora brassicae is an economically important pathogen of vegetable and oilseed Brassica crops. Severe infections can reduce both yield and marketability. In Korea, downy mildew of broccoli has occasionally been associated with complete yield loss in affected greenhouses, while infected tatsoi seedlings became unmarketable and were abandoned before harvest. The disease is also important in oilseed Brassica production overseas; severe epidemics have been documented in Australian canola. |
| References | Choi, Y. J., et al. 2012. Plant Dis. 96:1703. Gäumann, E. A. 1918. Beih. Bot. Centralbl. 35:395. Göker, M., et al. 2003. Can. J. Bot. 81:672. Hong, S. Y., et al. 2008. Plant Pathol. 57:777. Lee, H. J., et al. 2019. Res. Plant Dis. 25:98. Mohammed, A. E., et al. 2018. Plant Pathol. 67:1514. |
