The distribution of Fusarium species (Liseola section) and fumonisins B1, B2, and B3 (FB1, FB2, and FB3) in corn at the field stage to harvest time has been investigated. Corn samples were obtained from the 45th day after flowering to harvest stage, with 15 day intervals. A good correlation between fungal species and fumonisin contamination was observed. In particular, fumonisin contamination was higher in samples with fungal infection represented mainly by Fusarium moniliforme and Fusarium proliferatum, two well-known producers of fumonisins. Low levels of fumonisins were detected at the first and second samplings, when mainly Fusarium subglutinans, a fumonisin nonproducer species, was recorded. The three samplings after physiological maturity showed predominant F. moniliforme and F. proliferatum infection and a considerable contamination with fumonisins. In these samples the levels of FB1 averaged above 1 μg/g and FB2 and FB3 levels showed similar values but lower than FB1 values. This is the first report of fumonisins in Argentinian corn at field stages. Keywords: Fumonisins; Fusarium; corn; Argentina

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“Mal de Río Cuarto” (MRC) is the most important viral disease affecting corn in Argentina. Reovirus-like particles were observed in diseased plants (1,4) and were later serologically related to an isolate of maize rough dwarf virus (3), though this relationship was recently questioned (2). Based on estimates of the prevalence and severity of MRC and yield losses, government agencies, corn hybrid seed companies, and growers agreed that the worst epidemic in the country occurred during the 1996 to 1997 agricultural year. Approximately 300,000 ha of corn were affected by the disease and yield losses were estimated at $120 million. Affected areas included the central and southern Santa Fe, the central, northern, southeastern, and western Buenos Aires, and the eastern and southern (originally the endemic center of MRC in Río Cuarto County) parts of Córdoba. Virus infections were confirmed by double-antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) in root samples from each surveyed location, using an antiserum to MRC virus. The occurrence of MRC in non-endemic areas suggests an unusual phenological coincidence of high vector populations, abundant natural virus reservoirs, and susceptible stages in the crop. Most commercial hybrids surveyed were apparently susceptible to the virus, although some were tolerant. References: (1) O. E. Bradfute et al. Phytopathology 71:205, 1981. (2) C. Marzachi et al. Sem. Virol. 6:103, 1995. (3) R. G. Milne et al. Phytopathology 73:1290, 1983. (4) S. F. Nome et al. Phytopathol. Z. 101:7, 1981.

Soil biodiversity plays a key role in the sustainability of agriculture systems and indicates the level of health of soil, especially when considering the richness of microorganisms that are involved in biological control of soilborne diseases. Cultural practices may produce changes in soil microflora, which can be quantified through the isolation of target microorganisms. Rhizosphere soil samples were taken from an assay with different crop rotations and tillage systems, and populations of Trichoderma spp., Gliocladium spp. and actinomycetes were quantified in order to select the general and selective culture media that better reflect the changes of these microbial populations in soil. The most efficient medium for the isolation of Trichoderma spp. and Gliocladium spp. was potato dextrose agar modified by the addition of chloramphenicol, streptomycin and rose bengal, and for actinomycetes was Küster medium, with cycloheximide and sodium propionate.

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