| Distribution |
China, Korea, Taiwan |
| Characteristics |
Lesions commonly present on leaves, causing chlorosis of the affected tissues, pale green to yellow, polyangular, vein-limited, usually confined to small areas. Down present on the lower leaf surface, whitish, consisting of frost-like conidiophore outgrowth forming patches. Conidiophores (280–)314–366–418(–440) μm long, with the trunk 8–12 μm wide below the first branch, dichotomously branched, and with the first branch arising at 2/10–4/10 of the total conidiophore length. Branching occurs in 6–7(–8) orders. Callose plugs are often present in both the trunk and branches. Ultimate branchlets are reflexed to curved and 10–33 μm long. Vesicles (n = 50) are spherical, 6–10 μm in diameter, and bear 4–6 extensions, each 4–8 μm long; the tips of the extensions are obtuse to somewhat swollen and 1.5–2 μm wide. Conidia (n = 30) are ovoid, subhyaline, (15.0–)14.6–16.8–19.1(–26.3) × (12.5–)12.1–13.8–15.4(–20.0) μm, with a length/width ratio of (1.00–)1.09–1.22–1.36(–1.70); a pedicel is present. |
| Notes |
Bremia ovata is a host-specialized downy mildew associated primarily with Youngia japonica in East Asia. It was formerly treated within the broad B. lactucae complex, but morphological and multilocus phylogenetic analyses supported its recognition as an independent species (Choi et al., 2011). Broader multigene analyses confirmed B. ovata as a distinct lineage and demonstrated strong associations between Bremia lineages and their asteraceous hosts (Choi and Thines, 2015). Korean collections from Crepidiastrum denticulatum that had previously been assigned to B. ovata were subsequently demonstrated to represent the distinct species B. sawadae (Park et al., 2018). |
| Economic importance |
Youngia japonica is primarily a widespread wild herb, and B. ovata has little direct economic importance. No significant agricultural or commercial losses caused by this pathogen have been documented. |
| References |
Choi, Y. J., et al. 2011. Fungal Biol. 115:102.
Choi, Y. J., and Thines, M. 2015. PLoS ONE 10:e0133655.
Park, J. H., et al. 2018. Nova Hedwigia 107:303. |
