Fusarium meridionale is more aggressive and competitive than F. graminearum as a causal agent of Gibberella Ear Rot of maize in Brazil

In Brazil, Gibberella ear rot (GER) of maize is caused mainly by Fusarium meridionale (Fmer), while F. graminearum (Fgra) is a minor contributor. To test the hypothesis that Fmer is more aggressive than Fgra on maize, three experiments were conducted in the south (subtropical summer), and one in the central-south (tropical winter) of Brazil, totaling seven conditions (year ✕ location ✕ hybrid). Treatments consisted of Fgra or Fmer (two isolates of each) inoculated once four days after silk; alternately inoculated (Fgra⇾Fmer or Fmer⇾Fgra) six days apart; and (in central-south only) sequentially inoculated without alternating (Fmer⇾Fmer or Fgra⇾Fgra). Overall GER severity was higher in the south (37.0%) compared with the central-south (16.9%), likely due to the higher summer temperatures (20 to 25oC). In the south, severity was highest in Fmer treatments (67.8%); followed by Fmer⇾Fgra (41.1%); then Fgra⇾Fmer (19.4%); and lowest in Fgra (2.1%), suggesting an antagonistic relationship. In the central-south during winter (15 to 20oC), severity was generally higher (7.3 to 11.6%) in sequential inoculation treatments than when either species was inoculated alone. Only nivalenol (NIV) or deoxynivalenol (DON) were detected when Fmer or Fgra, respectively, were inoculated singly and sequentially with no alternation. Both toxins were found in grains harvested from the Fmer⇾Fgra treatment, while only NIV was found in kernels from the Fgra⇾Fmer treatment, suggesting that Fmer was more competitive than Fgra in co-inoculations. The dominance of Fmer as a cause of GER in Brazil may be due in part to its higher aggressiveness and competitiveness than Fgra.