| Distribution |
Korea |
| Characteristics |
Down hypophyllous, whitish to yellowish, dense, felt-like. Haustoria filling the host cell partly to almost completely, lobate. Conidiophores emerging through stomata, up to 20 in a fascicle, hyaline, somewhat stout, straight, (244.5–)328.5–410.2–491.9(–542.4) μm; trunk straight, (150–)200–300(–350) μm long, (7–)9–13(–16) μm wide (n = 30). Ultimate branchlets mostly in pairs, flexuous to sigmoid, (8.8–)11.7–16.8–21.8(–26.4) μm long, (1.1–)1.5–2.1–2.6(–3.0) μm wide at the base; tip obtuse or subtruncate (n = 30). Conidia hyaline, broadly ellipsoidal to subglobose, (18.2–)21.6–23.9–26.1(–29.1) μm long (av. 24.50), (17.7–)20.0–21.6–23.3(–24.3) μm wide (av. 21.29), a length to width ratio of (0.95–)1.04–1.10–1.17(–1.20), the greatest width median, rarely sub- or supra-median, tip and base rounded; pedicel mostly present as a scar. Resting organs not seen. |
| Notes |
Downy mildew on spider flower has historically been referred to Peronospora cleomes and Plasmopara venezuelana, but both names were invalidly published. Korean collections from Tarenaya hassleriana were morphologically distinct from H. parasitica sensu stricto and were provisionally identified as Hyaloperonospora sp. (Choi et al. 2012). Subsequent ITS and cox2 analyses placed the Korean lineage close to the H. brassicae complex, but nomenclatural and morphological uncertainties prevented formal description or combination (Lee et al. 2017). In 2020, Hyaloperonospora daughtreyae was described from T. hassleriana in the United States; however, it is distinct from the Korean lineage, demonstrating that at least two Hyaloperonospora species can infect spider flower (Salgado-Salazar et al. 2020). Therefore, the Korean pathogen is retained here as Hyaloperonospora sp. |
| Economic importance |
Spider flower is widely cultivated as an ornamental plant in public landscapes and private gardens. Downy mildew causes chlorotic leaf lesions, conspicuous whitish sporulation, and eventual necrosis, thereby reducing ornamental quality. In Korea, the disease has been observed in public garden plantings, and related downy mildew outbreaks on spider flower have also been documented overseas. |
| References |
Choi, Y. J., et al. 2012. Plant Dis. 96:588.
Lee, J. S., et al. 2017. Mycobiology 45:139.
Salgado-Salazar, C., et al. 2020. Eur. J. Plant Pathol. 157:311. |
