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First Report of Puccinia kuehnii, Causal Agent of Orange Rust of Sugarcane, in Brazil

In December 2009, on a farm located near the city of Rincão, state of São Paulo, Brazil, uredinial leaf lesions typical of a rust disease were observed to be affecting sugarcane (a complex Saccharum L. hybrid). Lesions were observed in a nursery plot of a precommercial cultivar (cv. Centauro) known to be resistant to brown rust caused by Puccinia melanocephala Syd. & P. Syd. Leaf samples, inspected under a light microscope, revealed spores identical morphologically to those described for the fungus P. kuehnii E.J. Butler, causal agent of sugarcane orange rust (1,3). Telia and teliospores were not observed. The Ministry of Agriculture was notified on 7 December 2009 in accordance with current Brazilian quarantine legislation. On 9 December, a specialized team from the Federal Phytosanitary Defense Department (DSV/MAPA) started a survey at the farm, collected leaf samples for additional analyses, and confirmed the presence of P. kuehnii E.J. Butler in Brazilian territory. During the following weeks, the disease was observed in several sugarcane-growing areas of the southern states of São Paulo and Paraná. It affected a small proportion of clones under selection in several breeding programs and the commercial cultivars SP89-1115, RB72454, and SP84-2025, which are now considered to be highly susceptible to the disease and currently cover less than 10% of the country's commercial sugarcane area. To our knowledge, this is the first report of P. kuehnii infecting sugarcane in Brazil, the largest world producer with more than 8 million ha of this crop. Orange rust is expected to expand to other important Brazilian sugarcane-producing areas, including the northeastern states and a new sugarcane expansion area in the central part of Brazil. The disease is widespread in the Asia-Pacific Region, caused a major epidemic in Australia in 2000, and was reported in the Western Hemisphere in 2007--2008 in several countries in North (1,2) and Central America (2,3) prior to this detection in South America.

References: (1) J. C. Comstock et al. Plant Dis. 92:175, 2008. (2) R. C. Flores et al. Plant Dis. 93:1347, 2009. (3) W. Ovalle et al. Plant Dis. 92:973, 2008.