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SPERMOGONIA (s) up to 130 diam, in circular groups, on the upper and under leaf surface.
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AECIA (a) formed in small, circuital groups, up to 5 mm diam, on the under leaf surface.
Peridium (p) cup-shaped, 0.2-0.3 mm diam, rarely cylindrical, up to 1.3 mm long, with a whitish, rugged edge.
Peridial cells almost isodiametric or slightly flattened, with a smooth, up to 13 µm thick outer wall and a 2.5-3.5 µm thick, warty inner wall.
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Wall thin, pale yellowish, thickened up to 5 µm at the top, ornamented with small warts evenly distributed on the whole surface and with larger warts more scattered on the surface, as well as with colourless tubercles, up to 2.5 µm diam.
UREDINIA (u) present on stems and leaf sheaths, sometimes on the upper leaf surface, 1-2 mm long, frequently connected with each other to form long, rusty-brown strips.
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UREDINIOSPORES (ue) elliptic or egg-shaped, (20-)28-38 x 17-21 µm.
Wall yellowish to ochre, 1.5-2.5 µm thick, ornamented with spines.
Germ pores 4, rarely 3-5, equatorial.
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TELIA (t) on stems and leaf sheaths, sometimes also on leaves, frequently connected with each other to form long strips, brownish black or black, rigid, not dusty.
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TELIOSPORES (te) clavate or longitudinally elliptic, usually with a rounded top, rarely sharpened or flattened, 38-51(-80) x 15-21 µm.
Wall smooth, yellowish, up to 2 µm thick when examined from a side, yellow brown and 5-10 µm thick at the top.
Germ pores usually indistinct; the pore of the upper cell present at its top, the pore of the bottom cell occur near the lateral wall.
Pedicel yellow brown, up to 70 µm long, persistent.
PLANT HOST AND DISTRIBUTION. Spermogonia and aecia of P. graminis occur on members of the genus Berberis and related genera (Majewski 1979). Uredinia and telia are present on numerous plant species of different genera of the family Poaceae.
Puccinia graminis is a cosmopolitan fungus (Smith et al. 1988).
NOTES. Puccinia graminis is the causal agent of black stem rust of small grains and grasses. Infected plants ripen prematurely and form fewer and smaller seeds, mainly because of the use of high amounts of assimilates and the disruption of the plant host epidermis by the fungus (Smith et al. 1988).
Puccinia graminis forms three formae speciales, i.e., f. sp. avenae, secalis, and tritici (Smith et al. 1988). Additionally, many races and taxa representing "physiologic" specialization at the cultivar level have been recognized.
Puccinia graminis can overwinter in both the sexual and asexual phase (Smith et al. 1988). The fungus forms telia with teliospores on maturing poaceous plants. The teliospores usually germinate and form two haploid (+) or (-) basidiospores only after having been subjected to alternate freezing and thawing, and/or wetting and drying. In spring, when new, young barberry leaves are formed, the basidiospores are transmitted by the air. Intercepted by barberry leaves, they infect them to form lesions with spermogonia on the upper leaf side and protoaecia (initial aecia with no aeciospores) on the under leaf side. The spermogonia produce haploid (+) or (-) spermatia in a slime. Then, insects transmit the slime on (+) or (-) receptive hyphae of other spermogonia. The nuclei of the spermatia go into the hyphae, and, thereby, fertilize heterothallic strains, multiply, and migrate downward into the aecial initials. Finally, some of the aecial initial cells are dikaryotized and the aecia start to produce aeciospores. The aeciospores infect the poaceous plant host, on which first uredinia with urediniospores, and then telia with teliospores appear.
REFERENCES
Majewski T. 1979. Grzyby (Mycota) XI. Podstawczaki (Basidiomycetes), Rdzawnikowce (Uredinales) II. Warszawa-Kraków, 462 pp.
Smith I. M., Dunez J., Lelliott R. A., Phillips D. H., Archer S. A. 1988. European handbook of plant diseases. Blackwell Scientific Publications.