Production of zearalenone, deoxynivalenol, nivalenol, and acetylated derivatives by Australian isolates of Fusarium graminearum and F-pseudograminearum in relation to source and culturing conditions

Australian isolates of Fusarium pseudograminearum (Fp = F. graminearum Group 1) and F. graminearum (Fg = F. graminearum Group 2) can produce mycotoxins including zearalenone (ZEA), 4-deoxynivalenol (DON), and nivalenol (NIV). Fp isolates from wheat and barley tillers in southern Queensland all produced ZEA and DON in culture, and one typical isolate also produced 3-acetyldeoxynivalenol. Most Fg isolates from wheat and sorghum grains in southern Queensland produced ZEA and DON and one typical isolate also produced 15-acetyldeoxynivalenol. Fg isolates from maize plants in northern Queensland were all ZEA and NIV producers, which was consistent with previous reports, and they also produced high concentrations of acetyl-nivalenols. ZEA and either DON or NIV production by cultures derived from different conidia (and ascospores in Fg isolates) varied by 4-18-fold for ZEA and 2-4-fold for DON/NIV production, and there were significant negative correlations between ZEA and either DON or NIV, indicating a common controlling process. The pattern of ZEA production was quite different between Fp and Fg, with ZEA production being relatively delayed in Fg. After 7 days incubation at 28degreesC on maize meal, one Fp isolate produced 49 mg ZEA/kg, but in both DON-producing and NIV-producing isolates of Fg, ZEA concentrations after 7 days were <1 mg/kg. ZEA and DON were produced on sorghum and combined wheat-barley grains as well as maize meal, although there were trends for maize meal to be more productive, probably due to greater surface area or different gaseous exchange. Low temperature incubation of a Fg DON-type isolate increased ZEA production, but did not affect either a Fg NIV-type isolate or a Fp isolate. Relationships between these patterns of mycotoxin production, pathogenicity, and implications for crop contamination are discussed.