First Report of Puccinia polysora on Corn in Argentina.

Corn (Zea mays L.) is an important crop in northwest Argentina but acreage has declined over the last several years due to disease problems. During the 2000 to 2001 growing season, leaf diseases were observed on corn growing in northeastern Tucumán Province (Departamiento Leales), which resulted in yield losses. One of the most prevalent diseases was caused by a rust fungus that produced both uredinial and telial stages. At the time of flowering 32% of the leaf area was infected, and 3 weeks later 69% was infected. Three rust fungi are known from corn (2), and this fungus was identified as Puccinia polysora Underw. based on the morphology of the two types of sori and spores (1). Although known from most tropical and subtropical regions, to our knowledge, this is the first report of P. polysora in Argentina (voucher BPI 841342). Tucumán Province, where the disease was observed, is a subtropical region with temperatures during the growing season >24°C and a relative humidity >90%. P. polysora has not been observed in the Pampas Humedas, the corn belt of Argentina, possibly because the area is more temperate than northwest Argentina and therefore the environment is not conducive to disease development or perhaps P. polysora has not been introduced into the region. References: (1) G. B. Cummins. The Rust Fungi of Cereals, Grasses and Bamboos. Springer-Verlag, New York, 1971. (2) J. K. Pataky. Rusts. Pages 35-38 in: Compendium of Corn Diseases, 3rd ed. The American Phytopathological Society, St. Paul, MN, 1999.