Influence of water activity and temperature on growth and production of trichothecenes by Fusarium graminearum sensu stricto and related species in maize grains.

Fusarium meridionale and F. boothii cause Gibberella Ear Rot (GER) in maize. This study determined the effects of temperature (5-35 °C) and water activity (0.90-0.995 aw) on the growth, and deoxynivalenol (DON) and nivalenol (NIV) production of F. meridionale and F. boothii strains in maize grains. Fusarium graminearum sensu stricto strains from wheat were also tested. The three Fusarium species grew best at 0.995 aw and 25 °C. Growth was absent or marginal at 0.90 aw regardless of temperature. F. meridionale and F. boothii were sensitive to 30 °C and more affected by water stress than F. graminearum sensu stricto. The highest DON levels were at 0.995-0.97 aw and 30 °C and at 0.97 aw and 20 °C for F. graminearum sensu stricto, and at 0.995-0.97 aw and 20 °C for F. boothii. Fusarium meridionale reached maximum NIV accumulation at 0.995 aw and 20 °C. This produced DON at negligible levels compared to the other two Fusarium species. Growth of F. meridionale and F. boothii was well adapted to the usual autumn high humidity and mild temperatures associated with GER in northwest Argentina. Control strategies during grain development should be taken into account to reduce the risk of the presence of DON and NIV in the harvested grains.