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Disease Note.

Rust on Jointweed, Reported Only from Florida, Also Occurs in Wisconsin. J. W. McCain, Department of Plant Pathology, University of Minnesota, St. Paul 55108. J. V. Groth, Department of Plant Pathology, University of Minnesota, St. Paul 55108. Plant Dis. 79:1187. Accepted for publication 21 August 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-1187A.

Rust of smartweeds (Polygonum spp), a cosmopolitan disease caused by Puccinia polygoni-amphibii Pcrs.:Pcrs., was found once on jointweed, labeled Polygonella articulata (L.) Meisn., on an 1898 herbarium specimen in the Missouri Botanical Gardens (MO), St. Louis (1). The specimen is from Appalachicola, Fla., but this host species is now recognized only as far south as North Carolina (2). The rusted portion kept by Arthur(1) is too scanty to verify the host, but the host specimen still at MO is now identified as Polygonella gracilis (Nutt.) Meisn. (D. Brunner, personal communication). We found this rust 1,160 km north in 1991 on true Polygonella articulata at Grantsburg, Wis. The urediniospores are 20 to 25 ? 16 to 18 ?m, the teliospores 30 to 38 ? 18 to 21 ?m (voucher specimen in the Minnesota Plant Pathology herbarium). An epidemic of this rust species in western Wisconsin in 1991 on black bindweed (Polygonum convolvulus L.) may have provided sufficient inoculum to infect the jointweed. The spores on the two hosts were identical (the urediniospores were slightly smaller and the teliospores slightly longer than reported in Arthur) (1). Black bindweed rust has been present, but not severe, at Grantsburg each year since 1991 but none of the many jointweed plants examined were infected.

References: (1) J. C. Arthur. North Am. Flora 7:382, 1920. (2) J. H. Horton, Brittonia 15:177, 1963.