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Disease Note.

Additional Coniferous Aecial Hosts of the Poplar Leaf Rusts, Melampsora larici-populina and M. medusae f. sp. deltoidae. G. New-combe, Washington State University, Puyallup, WA, 98371-4998. G. A Chastagner, and S. K. McDonald, Washington State University, Puyallup, WA, 98371-4998. Plant Dis. 78:1218. Accepted for publication 21 September 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-1218E.

In 1991, two poplar leaf rusts were discovered for the first time in the Pacific Northwest: Melampsora larici-populina Kleb., and M. medusae Thuem. f. sp. deltoidae. M. larici-populina had a reported aecial host range of four conifer species: Larix decidua Mill. (European larch), L. leplolepis (Siebold & Zucc.) Gord. (Japanese larch), L. occidentalis Nutt. (Western larch), and Pinus radiata D. Don. (Monterey pine) (1). M. medusae f. sp. deltoidae had been reported on only two conifer species, L. decidua and L. laricina (DuRoi) K. Koch. (Eastern larch) (2). To determine whether additional conifers might be attacked by the two new rusts, conifer seedlings were inoculated via natural basidiospore discharge in a growth room. Aeciospores resulting from successful infections were used to inoculate susceptible poplars so that the species could be identified by urediniospore morphology. Aecia of M. larici-populina were found on two previously unreported hosts, Pinus ponderosa Douglas ex P. Laws. & C. Laws, (ponderosa pine) and P. contorta Douglas ex Loud. (lodgepole pine), while aecia of M. medusae f.sp. deltoidae were found on five previously unreported hosts, L. occidentalis, Pseudotsuga menziesii (Mirb.) Franco (Douglas fir), P. contorta, P. ponderosa, and P. radiata. No infection was observed on seedlings of Picea (3 spp), Abies (3 spp.), Chamae-cyparis (2 spp.), and Tsuga, Cupressus, Thuja, and Cedrus (1 spp. each).

References: (1) G. Newcombe and G. A Chastagner. Plant Dis. 77:532, 1993. (2) L. Shain, Mycologia 80:729, 1988.