Common larch-willow rust -Melampsora capraearum

A number of rust fungi infect larch and willow trees. If the teliospores are present on upper surface of willow leaves, Melampsora caprearum can be easily differentiated by the thickened apex of the teliospores. Also on willow, the uredinial stage is more difficult to distinguish from other species of Melampsora. The inconspicuous spermagonial and aecial stages occur on larch in spring. Recent molecular studies have confirmed that these are distinct species that can be identified using molecular diagnostic tools (Nakamura et al. 1998, Pei et al. 2005). Pei & McCracken (2005) present a recent account of these rust fungi. Melampsora caprearum is the most common species of this genus on larch in Europe.

Melampsora capraearum Thum. 1879

Spermogonia amphigenous, type 3 (Hiratsuka, 1992).

Aecia hypophyllous, pale orange; aeciospores globose or broadly ellipsoid, 15-25 × 12-20 µm, finely and densely verrucose, walls 1.5-2 µm, thick, germ pores scattered.

Uredinia hypophyllous, occasionally epiphyllous, 1-3 mm; urediniospores globose or broadly ellipsoid, 14-26 × 13-23 µm, walls 2-4 µm thick, distantly echinulate, germ pores scattered; paraphyses capitate, 50-60 x 18-30 µm, walls thickened at apex, up to 6 µm.

Telia epiphyllous, subcuticular, 1 mm or more wide, dark reddish-brown; teliospores 25-45 × 7-17 µm, walls 1 µm thick at side, 5-10 µm thick above, with an apical germ pore.

See Hiratsuka (1992) and for a more detailed description.

Host range: Spermagonial and aecial stages on various species of Larix, mostly commonly on Larix decidua and L. leptolepis with one report on L. occidentalis and L. sibirica. The uredinial and telial stage on many species of Salix, mostly commonly on S. caprea.

Geographic distribution: Widespread in Europe, the Middle East and Asia. The few reports from North America are from one state, Vermont, over a century ago (Orton, 1898), although more recent specimens in BPI exist from Missouri confirmed by G. Cummins.

References:

Arthur, J.C., and Cummins, G.B. 1933. Rusts of the Northwest Himalayas. Mycologia 25: 397-406.

Dietrich, W., and Muller, J. 2001. [The rust fungi, smut fungi, and downy mildews in the Czech part of Krusne hory (Erzgebirge)]. Czech Mycol. 53: 89-118.

Foister, C.E. 1961. The economic plant diseases of Scotland. Techn. Bull. Dept. Agric. Fish. Scotland 1: 1-210.

Gjaerum, H.B. 1986. Rust fungi (Uredinales) from Iran and Afghanistan. Sydowia 39: 68-100.

Guo, L. 1989. [Uredinales of Shennongjia, China]. Fungi & Lichens Shennongjia, 107-156 pages.

Helfer, S. 1992. The rust diseases of willows in Britain. Proc. Roy. Soc. Edinburgh 98B: 119-134.

Hiratsuka, N. 1940. Uredinales collected in Korea IV. Bot. Mag. (Tokyo) 54: 433-437.

Iqbal, S.H., and Khalid, A.N. 1996. Material for the fungus flora of Pakistan. II. An updated check list of rust fungi (Uredinales) of Pakistan. Sultania 1: 39-67.

Nakamura, H., Kaneko, S., Yamaoka, Y., and Kakishima, M. 1998. Differentiation of Melampsora rust species on willows in Japan using PCR-RFLP analysis of ITS regions of ribosomal DNA. Mycoscience 39: 105-113.

Orton, W.A. 1898. A partial list of the parasitic fungi of Vermont. Vermont Agric. Exp. Sta. Annual Rep. 11: 1-21.

Pei, M.H., Bayon, C., and Ruiz, C. 2005. Phylogenetic relationships in some Melampsora rusts on Salicaceae assessed using rDNA sequence information. Mycol. Res. 109: 401-409.

Ryzhkin, D.V., and Levkina, L.M. 2004. Rust fungi of the North-East of Republic Mordovia. Mikol. Fitopatol. 38: 45-50.

Nomenclature

Specimens in BPI

Additional distribution data

Suggested citation: Yun, H.Y. Systematic Mycology and Microbiology Laboratory, ARS, USDA. . Invasive Fungi. Common larch-willow rust -Melampsora capraearum . Retrieved November 21, 2009, from http://nt.ars-grin.gov/sbmlweb/fungi/index.cfm .