Species diversity and toxigenic potential of Fusarium graminearum complex isolates from maize fields in northwest Argentina.

Members of the Fusarium graminearum species complex (Fg complex) are the causal agents of ear rot in maize and Fusarium head blight of wheat and other small grain cereals. The potential of these pathogens to contaminate cereals with trichothecene mycotoxins is a health risk for both humans and animals. A survey of ear rot isolates from maize collected in northwest Argentina recovered 66 isolates belonging to the Fg complex. A multilocus genotyping (MLGT) assay for determination of Fg complex species and trichothecene chemotypes was used to identify 56 of these isolates as F. meridionale and 10 isolates as F. boothii. F. meridionale was fixed for the nivalenol (NIV) chemotype, and all of the F. boothii isolates had the 15-acetyldeoxynivalenol (15ADON) chemotype. The results of genetic diversity analysis based on nine variable number tandem repeat (VNTR) loci supported the hypothesis of genetic isolation between F. meridionale and F. boothii, and provided little evidence of geographic substructure among populations of the dominant pathogen species, F. meridionale. This is the first study to indicate that F. meridionale and F. boothii may play a substantial role in the infection and trichothecene contamination of maize in Argentina. In addition, dominance of the NIV chemotype among Fg complex isolates from Argentina is unprecedented, and of significant concern to food safety and animal production.

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.