SPERMOGONIA (s) in rather compact conglomerations, up to 5 mm diam, hemispherical, protuberant, pale brown, blackening with age, 180-225 diam, with many receptive hyphae at the top, develop on yellow, later reddish, purple or brown spots on the outer leaf surface.
Peridium pale brown, up to 3 mm high and 1.5 mm diam, sharpened at the top. At maturity, the peridium bursts and forms yellowish, filiform strands, and becomes fusiform.
Peridial cells highly irregularly prolate, with inner and lateral walls highly thickened, up to 10 µm, ornamented with cylindrical or prolate warts, distributed in indistinct rows; inner cell walls thin, covered with fine warts.
AECIOSPORES (as) subglobose to elliptical, angular, 25-34 x 22-29 µm.
Wall yellow brown, 3-5 µm thick, ornamented with very fine warts.
Germ pores 6-9, irregularly distributed.
UREDINIA (u) unknown.
TELIA (t) form on twigs in tremellose, yellow brown conglomerations of a different size, up to 5-7 cm, when young, then dry, become brown black, up to 5 mm high.
TELIOSPORES (ts) fusiform to widely elliptical, tapering towards or sharpened at the top, rounded or more frequently narrowed at the base, constricted at the transverse wall, 37-63 x 20-33 µm.
Wall smooth, yellowish or yellow brown, 1.0-2.5 µm thick.
Germ pores 2-3 in each cell, usually positioned at the transverse wall, without distinct papillae.
Pedicel (p) colourless, dissolving.
PLANT HOST AND DISTRIBUTION. Spermogonia and aecia of G. sabinae develop on members of the genus Pyrus (Majewski 1979). Telia origin on Juniperus sabina L. and some other species of the genus Juniperus.
Gymnosporangium sabinae is widespread in Europe (Smith et al. 1988) and probably occurs all over the world (Majewski 1979).
NOTES. Gymnosporangium sabinae is the severe causal agent of rust of pear-tree (Agrios 1988).
Gymnosporangium sabinae has originally been described as G. fuscum DC. (Smith et al. 1988).
Apart from the disease symptoms presented above, G. sabinae can also cause perennial cankers on pear branches (Smith et al. 1988). These may be destructive on young trees, especially for the shape of the trees. On junipers, this fungus causes canker-like swellings of the shoots, on which brown telial "horns" bear the teliospores.
Agrios G. N. 1988. Plant pathology, 3rd edition, Academic Press, INC. San Diego, New York, Berkeley, Boston, London, Sydney, Tokyo, Toronto.
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.