The Dominance of Fusarium meridionale Over F. graminearum 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 Fusarium meridionale (Fmer), while F. graminearum (Fgra) is a minor contributor. To test the hypothesis that Fmer is more aggressive than Fgra 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 Fgra or Fmer (two isolates of each) inoculated once four days after silk; inoculated sequentially and alternately (Fgra⇾Fmer or Fmer⇾Fgra) six days apart; or (in the central-south) inoculated sequentially without alternating species (Fmer⇾Fmer or Fgra⇾Fgra). Overall, severity was two times greater in the south (37.0%) where summer temperatures were warmer (20 to 25oC) than in central-south. In the south, severity was greatest 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 (15 to 20oC), severity was generally higher in the sequential non-alternating inoculation treatments (Fmer⇾Fmer or Fgra⇾Fgra) than when either species was inoculated only once. Only nivalenol (NIV) or deoxynivalenol (DON) were detected when Fmer or Fgra, respectively, were inoculated singly, or 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 compared with Fgra.