Lemongrass, Cymbopogon citratus (DC.) Stapf. (Poaceae), is grown widely in the tropics and subtropics as an ornamental, flavoring ingredient in Asian cooking, and for tea and fragrant oil (3). In February 2013, rust symptoms were observed on lemongrass in several gardens in Miami-Dade County, Florida. Symptoms began as small chlorotic flecks on both leaf surfaces that became crimson and enlarged to streaks ~1 cm in length. On the abaxial side of leaves, erumpent streaks ruptured to produce pustules in which urediniospores formed. Eventually, streaks coalesced to produce large patches of tan to purplish necrotic tissue that blighted most of the leaf surface and was often surrounded by chlorotic borders. These symptoms, fungal morphology, and nuclear ribosomal large subunit (28S) DNA analysis were used to identify the pathogen as Puccinia nakanishikii Dietel. Urediniospores were pyriform to globose, orange to crimson, slightly echinulate, and somewhat longer than a previous report (32.1 ± 3.4 (27 to 42) × 23.3 ± 2.4 (21 to 27) μm vs. 22 to 28 × 22 to 25 μm) (2). Uredinia contained clavate paraphyses, but teliospores were not observed. No aecial host is known for this pathogen. A 28S DNA sequence that was generated with the NL1 and LR3 primers (1,4) was deposited in GenBank under accession no. KC990123; it shared 99% identity with GenBank accession GU058002, which came from a specimen of P. nakanishikii in Hawaii. Voucher specimens of affected leaves of lemongrass have been deposited at the Arthur Herbarium, Purdue University. Although this disease has been reported in California, Hawaii, New Zealand, and Thailand, this is believed to be the first report from Florida (2). Based on rainfall and temperature conditions that are conducive to its development in South Florida, it has the potential to significantly reduce the health and production of this plant in area gardens.
References: (1) C. P. Kurtzman and C. J. Robnett. Antonie Van Leeuwenhoek 73:331. 1998. (2) S. Nelson. Rust of Lemongrass. Univ. Hawaii PD-57, 2008. (3) USDA, ARS, GRIN Online Database. URL: http://www.ars-grin.gov/cgi-bin/npgs/html/taxon.pl?12797, accessed 25 April 2013. (4) R. Vilgalys and M. Hester. J Bacteriol. 172:4238, 1990.