Gaura lindheimeri Engelm. & A. Gray (Onagraceae) is an ornamental shrub that is native to southern Louisiana and Texas. Its texture and form make it a popular perennial border plant. In April 2010 and 2011, three collections of Guara leaf samples with signs and symptoms of a rust disease were made from a home garden in Baton Rouge, LA. Infected leaves showed chlorotic lesions on the adaxial surface and were associated with scattered, hypophyllous uredinia. Urediniospores were globose to obovoid, echinulate, had two equatorial germ pores, and measured 16 to 21 × 18 to 25 μm with a wall 2 μm thick. Telia and teliospores were not observed on any of the collected samples. The pathogen was identified as Uromyces plumbarius Peck on the basis of the uredinial characters compared with four U.S. National Fungus (BPI 1103868, 0013551, 0013554, and 0013557) collections of U. plumbarius. The three collections from Louisiana have been deposited in the Bernard Lowy Mycological Herbarium. DNA was extracted from all three specimens and the nuclear ribosomal large subunit (28S) was amplified according to the protocol outlined by Aime (1). The three Louisiana collections had identical large subunit sequences (GenBank Accession Nos. JQ312670, JQ312671, and JQ312672). No sequences of U. plumbarius were available for comparison in GenBank; a BLAST search was 99% similar over 100% query coverage to Puccinia dioicae Magnus (Accession No. GU058019) and P. silvatica J. Schröt. (Accession No. AY222048). The uredinial/telial hosts of P. dioicae and P. silvatica are in the Cyperaceae, whereas U. plumbarius is an autoecious rust on Onagraceae. It is interesting to note that the aecial stage of P. dioicae occurs on Onagraceae and that it has a high sequence identity to U. plumbarius, supporting the hypothesis that these are correlated species (2). U. plumbarius has been recorded on several species of Gaura within the United States. To our knowledge, this is the first record of U. plumbarius in Louisiana and the first report of U. plumbarius on G. lindheimeri.
References: (1) M. C. Aime. Mycoscience 47:112, 2006. (2) C. R. Orton. Mycologia 4:194, 1912.