| Characteristics |
Lesions commonly causing discoloration of the tissues, pale green or yellow, later becoming dark brown, vein-limited, polyangular, frequently covering larger areas by coalescing; infected tissues become necrotic. Down present on the lower surface of host leaves, whitish, consisting of scattered conidiophores, sparse, with only one or two in a fascicle. Conidiophores emerging through stomata, hyaline, straight, (240–)357–449–541(–560) μm long; trunk straight, (60–)100–150–200(–300) μm long, (4.9–)6.5–7.7–9.3(–10.9) μm wide below the first branch; basal end not differentiated to slightly bulbous, (6.4–)8.6–10–11.4(–12.2) μm wide; callose plugs often present in trunk and branches; branches dichotomous, with 3–5(–6) branching orders. Ultimate branchlets mostly paired, rarely single, slightly curved to substraight, 8–13 μm long, tips obtuse to somewhat swollen; vesicles spherical or confluent, 8–12 μm diam., bearing 4–6 extensions 6–8 μm long. Conidia hyaline, oblong to ovoid, almost symmetrical at the equatorial plane, (13.8–)14.5–16.8–19.1(–27.2) μm long, (13.5–)14.5–15.9–17.3(–21.7) μm wide, with a l/w ratio of (0.94–)0.98–1.06–1.14(–1.26), greatest width median to submedian, apex rounded, base broadly rounded; pedicel mostly present, forming a thin-walled papilla. Conidia germinating directly by a germ tube emerging from the apex, up to 215 μm long and rarely branched. Resting organs not observed. |
| Notes |
Bremia itoana is a host-specialized downy mildew pathogen of Crepidiastrum sonchifolium, an East Asian member of the Asteraceae. The pathogen was initially presumed to belong to the broadly defined B. lactucae complex, but morphological comparisons and multilocus phylogenetic analyses demonstrated that isolates from C. sonchifolium form a strongly supported lineage distinct from all previously recognized species of Bremia. Accordingly, B. itoana was described as a new species by Choi et al. (2018). The species differs from other East Asian Bremia species occurring on related genera of Crepidinae in both its phylogenetic position and morphological characters, including the shape of the conidia, ultimate branchlets, and apical vesicles. |
| Economic importance |
Crepidiastrum sonchifolium is an edible vegetable native to East Asia and is locally cultivated and consumed in Korea. The plant has traditionally been used for making kimchi, and the species is also included among regional folk plants used for food and other traditional purposes in Korea (Song et al. 2013; Park and Chun 2015). In Korea, downy mildew on C. sonchifolium was initially observed in a private farm in Chuncheon and was subsequently found in commercial farms in other regions, indicating that the disease has become established in cultivated populations of this vegetable (Choi et al. 2018). Although quantitative yield losses caused by B. itoana have not been documented, severe infection produces chlorosis, necrosis, and deterioration of leaves, which may directly reduce the quality and marketability of this vegetable. |
| References |
Choi, Y. J., et al. 2018. Mycobiology 46:416.
Park, M. S., and Chun, Y. M. 2015. Korean J. Plant Resour. 28:79.
Song, M. J., et al. 2013. Indian J. Tradit. Knowl. 12:177. |
