Polystigma rubrum (Pers.) DC., Fl. franç., Edn 3 (Paris) 5/6: 164 (1815)
Index Fungorum number: IF182352
Parasitic on Prunus stepposa Kotov. Leaf spots developing on living leaves, dispersed, uneven, swollen, pigmented, bordered by healthy leaf tissue. Asexual morph: Conidial stromata irregularly-shaped, roughly orbicular, orange to reddish-brown, becoming darker in the central region, developing within and throughout the leaf tissue. Stromatal tissue comprising upper and lower plant tissue layers 35–40 μm thick whose cells are filled with shiny orange material, and an intermediate layer 180–220 μm thick composed almost completely of occluded angular to vertically elongated fungal cells. Conidiomata 119–185 µm high, 84–130 µm diam (x̅ = 147.7 × 104.3 µm, n = 7), roughly globose. Ostiole epigenous, barely conspicuous. Conidiomatal wall inadequately developed, not properly discernable from the stromatal tissue. Conidiogenous cells 9–28 µm × 1–3 µm (x̅ = 16.3 × 1.8 µm, n = 42) spanning the inner surface of the wall, produced horizontally from successive cells of short conidiophores derived from a thin layer of hyaline thin-walled cells of textura angularis, initially cylindrical but progressively tapering towards apex, which appears faintly irregular owing to successive conidial scars resulting from sympodial proliferation. Conidia 17–38 µm × 0.4–1.1 µm (x̅= 25.9 × 0.7 μm, n = 34), the lower part lanceolate to fusiform, the upper part filiform, sigmoidally curved to hooked, the base ± truncate, hyaline, aseptate, apparently smooth-walled. Sexual morph: illustrated in Cannon 1996.
Polystigma rubrum (Material examined – RUSSIA, Rostov region, Shakhty City, Cotton fabric microdistrict, torn shrubs near Grushevka river on Prunus stepposa Kotov., 9 October 2017, Timur S. Bulgakov, T-2093, MFLU 18-0271). a Swollen leaf spots on Prunus stepposa K. b Close-up of leaf spots. c Vertical section through conidioma. d Conidiogenous cells and developing conidia. e Conidiomatal wall. f-h Conidia. Scale bars: a = 200 μm, c = 50 μm, d-h = 10 μm (image from Hyde et al. 2020).