Canna lily is a monocot, herbaceous perennial ornamental plant in the Cannaceae that is native to tropical South America and cultivated throughout the southern United States. Canna lily is a popular garden and landscaping plant and a large horticultural industry depends on this plant. In September 2008 and again in November 2009, two species of Canna lily (Canna × generalis L.H. Bailey and C. indica L.) were found to be severely infected with rust disease in three garden locations in southern Louisiana (East Baton Rouge Parish, Lafayette Parish, and Orleans Parish). Diseased samples from both host species and all locations exhibited similar symptoms of numerous, yellowish brown, subepidermal, erumpent, and irregular-shaped uredinia on both leaf surfaces. Initially, sori were scattered, later covering the entire leaf with coalescing pustules. Urediniospores were subglobose to ovoid or pyriform, echinulate, and measured 25.74 to 37.18 (–38.61) × 17.16 to 27.17 (–28.6) μm, with thickened apical walls, 1.3 to 1.6 μm, and one to two equatorial germ pores. Telia and teliospores were not observed on any of the collected samples. Pathogen identity was confirmed as Puccinia thaliae Dietel by nuclear ribosomal large subunit (28S) DNA sequencing with rust-specific primers (1). The sequence (deposited in GenBank as No. HQ434482), when blasted, was found to match sequence No. EU851154 of P. thaliae from C. indica with 98% identity (719 of 730 bp), the differences being attributed to a single insertion at bp 423 to 436 of sequence No. EU851154. The sequences of P. thaliae obtained from two different samples from Louisiana were identical and did not match any other sequence in GenBank. In North America P. thaliae is reported to cause rust on C. indica L. in Florida and C. × generalis in Texas, as well as on two members of the Marantaceae (Maranta arundinacea L. and Thalia geniculata L.) in Florida and M. arundinaceae in Mexico (2). To our knowledge, this is the first report of P. thaliae in Louisiana on Canna lily. Voucher materials (C. × generalis = LSU00123378 and C. indica = LSU00123384) have been deposited in the Bernard Lowy Mycological Herbarium (LSUM).
References: (1) M. C. Aime. Mycoscience 47:112, 2006. (2) D. F. Farr and A.Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved 12 February from http://nt.ars-grin.gov/fungaldatabases/, 2010.