The Dominance of Over Causing Gibberella Ear Rot in Brazil May Be Due to Increased Aggressiveness and Competitiveness.

In Brazil, Gibberella ear rot (GER) of maize is caused mainly by , whereas is a minor contributor. To test the hypothesis that is more aggressive than 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 or (two isolates of each) inoculated once 4 days after silk, inoculated sequentially and alternately ( or ) 6 days apart, or (in the central-south) inoculated sequentially without alternating species ( or ). 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 treatments (67.8%); followed by (41.1%), then (19.4%), and lowest in (2.1%), suggesting an antagonistic relationship. In the central-south (15 to 20°C), severity was generally higher in the sequential nonalternating inoculation treatments ( or ) than when either species was inoculated only once. Only nivalenol (NIV) or deoxynivalenol was detected when or , respectively, was inoculated singly, or sequentially with no alternation. Both toxins were found in grains harvested from the treatment, whereas only NIV was found in kernels from the treatment, suggesting that was more competitive than in coinoculations. The dominance of as a cause of GER in Brazil may be due in part to its higher aggressiveness and competitiveness compared with .