The Dominance of <i>Fusarium meridionale</i> Over <i>F. graminearum</i> Causing Gibberella Ear Rot in Brazil May Be Due to Increased Aggressiveness and Competitiveness

Abstract

In Brazil, Gibberella ear rot (GER) of maize is caused mainly by <i>Fusarium meridionale</i>, whereas <i>F. graminearum</i> is a minor contributor. To test the hypothesis that <i>F. meridionale</i> is more aggressive than <i>F. graminearum</i> on maize, six experiments were conducted in the south (summer) and one in the central-south (winter), totaling seven conditions (year × location × hybrid). Treatments consisted of <i>F. graminearum</i> or <i>F. meridionale</i> (two isolates of each) inoculated once 4 days after silk, inoculated sequentially and alternately (<i>F. graminearum → F. meridionale</i> or <i>F. meridionale → F. graminearum</i>) 6 days apart, or (in the central-south) inoculated sequentially without alternating species (<i>F. meridionale → F. meridionale</i> or <i>F. graminearum → F. graminearum</i>). Overall, severity was two times greater in the south (37.0%), where summer temperatures were warmer (20 to 25°C) than in central-south. In the south, severity was greatest in <i>F. meridionale</i> treatments (67.8%); followed by <i>F. meridionale → F. graminearum</i> (41.1%), then <i>F. graminearum → F. meridionale</i> (19.4%), and lowest in <i>F. graminearum</i> (2.1%), suggesting an antagonistic relationship. In the central-south (15 to 20°C), severity was generally higher in the sequential nonalternating inoculation treatments (<i>F. meridionale → F. meridionale</i> or <i>F. graminearum → F. graminearum</i>) than when either species was inoculated only once. Only nivalenol (NIV) or deoxynivalenol was detected when <i>F. meridionale</i> or <i>F. graminearum</i>, respectively, was inoculated singly, or sequentially with no alternation. Both toxins were found in grains harvested from the <i>F. meridionale → F. graminearum</i> treatment, whereas only NIV was found in kernels from the <i>F. graminearum → F. meridionale</i> treatment, suggesting that <i>F. meridionale</i> was more competitive than <i>F. graminearum</i> in coinoculations. The dominance of <i>F. meridionale</i> as a cause of GER in Brazil may be due in part to its higher aggressiveness and competitiveness compared with <i>F. graminearum</i>.