Thekopsora areolata

Thekopsora areolata as Pucciniastrum areolatum is listed by APHIS as an organism of quarantine significance for the United States. It is a heteroecious rust that produces uredinia and telia on Prunus and some other members of the Rosaceae. Aecia are produced on cones of Picea and sometimes on young stems where the rust can cause twisting and distortion (Hansen and Lewis 1997).

Thekopsora areolata (Fr.:Fr.) Magnus, Sitzungsbericht der Gesellschaft naturfoschender Freunde zu Berlin p. 58. 1875.

Spermogonia gregarious, subcuticular.

Aecia grouped, covering inner surface of scales on lower part of cones, rarely on outer side of scales, subepidermal, sometimes erumpent, hemispherical or polygonal, 0.8-1.2 mm across, 0.8-1 mm high, reddish brown to dark brown; peridia firm, peridial cells irregularly polygonal, 25-38 × 18-27 µm, yellowish brown, outer walls 10-22 µm thick, smooth, inner walls 2-3 µm thick, verrucose; aeciospores globose, ovate or ellipsoid, somewhat angular, 16.5-30 × 15-22 µm, walls up to 6 µm thick, strongly verrucose, sometimes with an inconspicuous, narrow, linear area on one edge of aeciospore.

Uredinia hypophyllous, subepidermal becoming erumpent, scattered or grouped, in areas limited by veins, angular, violet or reddish brown spots on upper leaf surface, round or oblong, 0.08-0.4 mm across, often pulverulent, orange-yellow; peridia hemispherical, delicate, peridial cells isodiametrically to irregularly polygonal, 7-15 µm across, walls thin, smooth, colorless, inner walls gradually thickened toward ostiole, ostiolar cells larger, oblong, up to 21 µm high; urediniospores globose, subglobose, ellipsoid or ovate, 14.5-25.5 × 12-18 µm, walls colorless, finely echinulate, thin, 2-3 µm thick, pores 7-8, scattered, obscure.

Telia amphigenous, mostly epiphyllous, intracellular, limited by veins, eventually causing dark brown to blackish brown discoloration on leaf surface; teliospores in epidermal cells, globose, subglobose or ovate, somewhat polygonal, divided into 2-5 cells (mostly 4) by longitudinal or oblique septa, 16-23 µm high × 13.5-27 µm diam, walls 0.8-1.2 µm thick, smooth, yellowish brown, darker and up to 2-3 µm at apex (Hiratsuka et al. 1992).

Hosts: spermogonial and aecial stages on lower part of cones of species of Picea (Pinaceae); uredinial and telial stages mainly on living leaves of Prunus; also Amygdalus, Cerasus, and Padus (Rosaceae).

Geographic Distribution: Europe and Asia. There is one report from Dominican Republic, which could not be confirmed.

The genus Thekopsora is characterized by having cylindrical aecia of the Peridermium-type, irregularly polyhedric peridial cells, and globose, subglobose to irregularly polyhedrical aeciospores. Uredinia of this genus are subepidermal and of the Milesia-type, peridial cells are irregularly polygonal with conspicuous cells at ostiole. Telia are amphigenous and teliospores form within the epidermal cells of living leaves. The latter are 3-6 celled with vertical septa and one central germ pore per probasidial cell (Cummins & Hiratsuka 2003).

Of the thirteen species in the genus Thekopsora, only Thekopsora areolata and T. pseudo-carasi Hirats. f. were described with telial stages on Rosaceae. Thekopsora areolata has globose, subglobose, ellipsoid or ovate urediniospores measuring 14-25 × 10-18 µm, while urediniospores of T. pseudo-carasi are ovate, ellipsoid, or oblong and measure 19-31 × 12-19 µm. Additional species in Thekopsora include T. menziesiae Hirats. f., T. minima P. Syd. & Syd. (see Sato et al. 1993), T. sparsa (G. Winter) Magnus, T. tripetaleiae Hirats. f., and T. vaccinii (G. Winter) Hirats. f., all producing the telial stages on Ericaceae; T. rubiae Kom., T. nipponica Hirats. f., and T. guttata (J. Schröt.) P. Syd. & Syd. producing the telial stages on Rubiaceae; T. asterum Tranzschel with telial stage on Asteraceae; T. hydrangeae Magnus with telial stage on Hydrangeaceae; and T. brachybotrydis Tranzschel with telial stage on Boraginaceae. Hiratsuka (1958) suggested that two species of Uredo, U. gautheriae (P. Syd. & Syd.) Hirats. f. and Uredo ericae A. Naumann, are anamorphs of Thekopsora. They produce uredinial stages on Ericaceae.

The aecial and spermogonial stages of T. areolata are on Picea where conspicuous peridermioid aecia are produced on the cones (Hansen and Lewis 1997).

References:

Hansen, E.M., and Lewis, K.J. 1997. Compendium of Conifer Diseases. APS Press, St. Paul, Minnesota, 101 pages.

Hiratsuka, N. 1958. Revision of taxonomy of the Pucciniastreae with Special Reference to Species of the Japanese Archipelago. KASAI Publishing and Printing Co., Tokyo, 167 pages.

Sato, S., Katsuya, K., and Hiratsuka, Y. 1993. Morphology, taxonomy and nomenclature of Tsuga-Ericaceae rusts. Trans. Mycol. Soc. Japan 34: 47-62.

Nomenclature

Specimens in BPI

Additional distribution data

Suggested citation: Hernández, J.R. Systematic Mycology and Microbiology Laboratory, ARS, USDA. 12 October 2005. Invasive Fungi. Thekopsora areolata. Retrieved November 21, 2009, from http://nt.ars-grin.gov/sbmlweb/fungi/index.cfm .