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Title: First report of Puccinia kuehnii, causal agent of orange rust of sugarcane, in Guatemala

item Comstock, Jack
item Glynn, Neil
item Castlebury, Lisa

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/14/2008
Publication Date: 6/1/2008
Citation: Ovalle, W., Comstock, J.C., Glynn, N.C., Castlebury, L.A. 2008. First report of Puccinia kuehnii, causal agent of orange rust of sugarcane, in Guatemala. Plant Dis. 92:973

Interpretive Summary: This report of orange rust in Guatemala documents the second occurrence in the Western Hemisphere. Previously, it was reported in Florida and with its detection and widespread occurrence in Guatemala approximately 2 months later it may have been introduced to both locations around the same time. It has intermediate symptoms on the major cultivar, CP 72-2086. The impact of orange rust on the commercial production in Guatemala will have to be evaluated.

Technical Abstract: In September 2007, at Masagua, Escuintla Department, Guatemala , uredial lesions were observed on a sugarcane (a complex hybrid of Saccharum L. species) cultivar (CP 72-2086) considered resistant to brown rust caused by Puccinia melanocephala Syd. & P. Syd. that appeared different from those of brown rust. Samples were sent to the USDA-ARS Systematic Mycology and Microbiology Laboratory in Beltsville, Maryland, for identification. Observed morphological features were consistent with Puccinia kuehnii E.J. Butler and appeared similar to orange rust samples obtained from Florida in July (2). Uredinial lesions were hypophyllous, orange and variable in size, measuring 650–850 × 26–32 µm. Urediniospores were mostly obovoid to pyriform or broadly ellipsoidal, variable in size, 32–45 × 25–30 µm, and moderately echinulate with evenly distributed. Urediniospore walls were orange to light cinnamon brown, 1–2.5 µm thick with a pronounced apical wall and 4–5 equatorial pores. Telia and teliospores were not observed. The nuclear large subunit rDNA region of the rust infecting cultivar CP 72-2086 (BPI , GenBank Accession No. EU1) and the ITS1, 5.8S and ITS2 rDNA regions (GenBank Accession No. EU) were sequenced (1,3). DNA sequences were identical to sequences of P. kuehnii and distinct from known sequences of P. melanocephala available in GenBank (3). Five additional cultivars were evaluated using morphological characters and all six cultivars were rated as to their relative resistance. Cultivars CP 72-2086, CP 88-1508 and CP 89-2143 had an intermediate reaction; whereas cultivars, CP 72-1312, CP 73-1547 and CP 88-1165 were highly resistant (without symptoms) based on natural infection. Based on symptoms of orange rust CG 96-59 and CG 96-135 were resistant, CG 96-40 and CG 98-121 were intermediate and CG 96-52, CG 98-0115 and SP 79-2233 were susceptible based on natural infection. Orange rust was previously reported in Florida (2) and this is the second report of its occurrence in the Western Hemisphere. References: (1) Aime, M.C. 2006. Mycoscience 47:112. (2) Comstock et al., 2008. Plant Disease ???? (3) Virtudazo, E.V. et al. 2001. Mycoscience 42: 447