SPERMOGONIA (s) formed in small conglomerations on the upper leaf side and on stems.
Peridium composed of colourless, angular cells.
AECIOSPORES (ae) globose or irregularly elliptical, usually slightly angular, 20-26 x 17-21 µm.
Wall colourless, 2-2.5 µm thick, ornamented with small warts spaced 2-2.5 µm apart.
UREDINIA (u) naked, yellow, dusty, up to 0.3 mm diam, with many cylindrical or slightly clavate, curved, colourless, and thin-walled uredinial paraphyses (up) at the edge, formed on the under leaf side; on the upper leaf surface, directly above the uredinia, small, yellowish spots are present.
UREDINIOSPORES (ue) globose, widely elliptical or inversely egg-shaped, 20-26 x 15-21 µm.
Wall colourless, up to 1.5 µm thick, ornamented with small warts, spaced ca. 2 µm apart.
Germ pores indistinct.
TELIA (t) black, dusty, up to 0.5 mm diam, frequently connecting with each other to form large conglomerations.
TELIOSPORES (te) consist of 5-8, rarely 9 cells, not constricted at the transverse septa, 50-75(-90) x 25-28 µm, rounded at the base, slightly narrowed at the top, with a yellowish, at the base slightly darker coloured, process, 6-10 µm long.
Wall colourless to pale yellow in young teliospores, dark brown in mature spores, up to 5 µm thick, covered with unevennesses and irregular warts, frequently almost smooth at the base.
Germ pores usually 3 in each cell.
Pedicel colourless, yellowish in the upper part, highly thickened in the lower part, 70-125 µm long.
PLANT HOST AND DISTRIBUTION. Spermogonia, aecia, uredinia, and telia of P. mucronatum occur on different plant species of the genus Rosa (Majewski 1979).
Phragmidium mucronatum is cosmopolite (Majewski 1979).
NOTES. Phragmidium mucronatum usually overwinters in the form of teliospores associated with fallen leaves, rarely as mycelium in infected stems of its plant host (Brooks 1953; Kochman 1979). In spring, teliospores germinate to form basidiospores, being the source of the primary infection, resulting in the formation of spermogonia with receptive hyphae on the upper leaf surface and aecial initials on the under leaf side. The fungus is heterothallic. Therefore, aecia can produce aeciospores after the fertilization of the receptive hyphae of the spermogonium only by spermatia of the opposite and compatible strain. Then, the nucleus of the spermatium enters the receptive hypha, multiplies, and migrates downward into the aecial initial. Finally, some of these cells are dikaryotized and the aecium begins to produce aeciospores. Aecia can also origin from overwintered mycelium in infected stems of the plant host (Brooks 1953; Kochman 1973).
Brooks F. T. 1953. Plant diseases. Geoffrey Cumberlege. Oxford University Press. London, New York, Toronto.
Kochman J. 1973. Fitopatologia. PWRiL. Warszawa.
Majewski T. 1979. Grzyby (Mycota) XI. Podstawczaki (Basidiomycetes), Rdzawnikowce (Uredinales) II. Warszawa-Kraków, 462 pp.