Variable Rubus-Gerwasia variabilis

The rust fungi on Rubus are numerous and difficult to distinguish. Some species such as Gerwasia. variabilis are not frequently collected and may be synonyms of more commonly known taxa. Most rust species in the genus Gerwasia do not seem to pose a threat to species of Rubus in North America. Gerwasia variabilis occurs on species of Rubus native to the Andes in South America.

Gerwasia variabilis (Mayor) Buritica 1994

Uredinia epiphyllous (on upper surface of leaves), rarely hypophyllous (on lower surface of leaves), gregarious, round spots, up to 6 mm diam, dark brown to pale yellow brown, scattered, round or oblong, more or less confluent, at first covered by epidermis then splitting, yellowish then whitish.

Urediniospores subglobose or often ovoid, ovate or ellipsoid, 21-35 × 17-25 µm, rarely up to 40 µm long, hyaline, walls about 2 µm thick, apical walls not thickened, moderately separated minute warts.

Telia hypophyllous, more or less numerous, scattered, not confluent, tiny dots close together, soon exposed, without spots, gray-yellow or gray-brown.

Teliospores variable, two types of teliospores: a) oblong or ellipsoid, 39-50 × 14-20 µm, slightly brown, often subhyaline at base, rounded at both ends or attenuate at base, germ pore apical, walls 1 µm, apex walls gradually and not always thicker, barely 3 µm; pedicel hyaline, persistent, up to 25 x 5-7 µm; b) ovate or pyriform, often cuneate 35-52 × 18-26 µm wide above, 12-15 µm wide below, slightly brown, base attenuate or rarely rounded, apex rounded, more or less truncate and deeply lobed, lobes more or less numerous, up to 10 or more, rounded, up to 4 µm long and 4 µm wide, with apical germ pore, walls 1.5-2 µm thick, apex up to 7 µm thick; pedicel, hyaline, persistent, up to 30 x 5-7 µm.

Host range: Species of Rubus native to the Andes in South America, known from R. floribundus, R. guianensis, R. megalococcus, and R. nubigenus.

Geographic distribution: Known primarily from South America, Colombia, Ecuador, and Venezuela; also reported from South Africa based on an intercepted specimen housed at BPI.

Notes: This rust species is apparently confined to species of Rubus native to the Andes. Whether it can infect economically important species is unknown. Jackson (1931) provides a key to most species of Gerwasia (as Mainsia).

See Salazar-Yepes et al. (2007 as Morispora variabilis) for a more detailed description of G. variabilis.

References:

Chardon, C.e., and Toro, R.A. 1930. Mycological explorations of Colombia. J. Dept. Agric. Porto Rico 14: 195-369.

Jackson, H.S. 1931. The Rusts of South America based on the Holway Collections - III. Mycologia 23: 96-116.

Kern, F.D., Thurston Jr., H.W., and Whetzel, H.H. 1934. Uredinales. Monogr. Univ. Puerto Rico, B 2: 262-303.

Salazar-Yepes, M., Pardo Cardona, V.M., and Buritica, P. 2007. Species from Colombia, Ecuador and Peru belonging to the genus Gerwasia Raciborski from the order Uredinales. Caldasia 29: 105-120.

Watson, A.J. 1971. Foreign bacterial and fungus diseases of food, forage, and fiber crops. U.S.D.A. Agricultural Research Service : 111.

Nomenclature

Specimens in BPI

Additional distribution data

Suggested citation: Yun, H.Y. Systematic Mycology and Microbiology Laboratory, ARS, USDA. . Invasive Fungi. Variable Rubus-Gerwasia variabilis. Retrieved November 21, 2009, from http://nt.ars-grin.gov/sbmlweb/fungi/index.cfm .