Toxicity of Diplodia maydis in farm and laboratory animals

The acute toxicity of maize culture material of eight strains of Diplodia maydis in ducklings, as well as the ability of five of these strains to induce typical diplodiosis (a neuromuscular disease) in cattle and sheep was shown. Typical diplodiosis was induced in 17 sheep and 11 cattle. Two of the five toxic strains were isolated from maize involved in diploidiosis outbreaks, the others from commercial maize. Strains inducing diplodiosis could be isolated from commercial maize from the USA, Argentina and South Africa. There was no correlation between the toxicity of D. maydis strains in ducklings and their ability to induce diplodiosis in cattle and sheep. Some isolates were acutely toxic to ducklings and rats but were unable to induce diplodiosis in either cattle or sheep. Others, equally toxic to ducklings and rats, induced diplodiosis in cattle and sheep at low dose levels. Two doses, each of 5 g/kg, of maize culture material of isolates from the USA, Argentina and South Africa induced diplodiosis in sheep. Culture material incubated for less than 8 wk could not induce diplodiosis in cattle. Acute toxicity in ducklings and rats also increased with longer incubation periods. Cultures of non-sporulating and profusely sporulating strains were equally toxic to ducklings. Heat treatment of culture material for 48 days at 45 degrees C failed to reduce toxicity in ducklings.