| Characteristics |
Lesions commonly present on leaves, causing discoloration of the affected tissues, initially pale green to yellow, later becoming brown to greyish, indistinct in outline, with diffuse margins, frequently covering larger areas by coalescing. Down present on the lower leaf surface, corresponding exactly to the lesions, whitish, consisting of effuse conidiophore outgrowth forming patches. Conidiophores (460–)432–547–662(–850) μm long, with the trunk 8–13 μm wide below the first branch, dichotomously or monopodially branched, and with the first branch arising at 3/10–6/10 of the total conidiophore length, mostly near the midpoint. Branching occurs in 5–6 orders. Callose plugs are often present in both the trunk and branches. Ultimate branchlets are slightly curved to substraight and 10–25 μm long. Vesicles (n = 50) are spherical, 8–11 μm in diameter, and bear 5–6 extensions, each 4–11 μm long; the tips of the extensions are obtuse to somewhat swollen and 1.5–2 μm wide. Conidia (n = 30) are oblong to ovoid, subhyaline, (13.8–)15.4–16.8–18.2(–20.0) × (12.5–)14.1–15.3–16.6(–17.5) μm, with a length/width ratio of (1.00–)1.04–1.10–1.16(–1.17); the pedicel is absent or, rarely, short and conical. |
| Notes |
Bremia microspora is an East Asian downy mildew associated with Ixeris and closely related hosts. Although historically included in the broad concept of B. lactucae, extensive morphological comparisons and multilocus phylogenetic analyses supported its recognition as a distinct, host-specialized species (Choi et al., 2011). Subsequent multigene analyses further confirmed its distinct phylogenetic position and demonstrated that diversification within Bremia has largely involved host shifts followed by specialization (Choi and Thines, 2015). Some Korean collections from Ixeris polycephala previously identified as B. microspora were later shown to represent the distinct species B. polycephala (Park et al., 2018). |
| 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. |
