Gibberella ear and stalk rot caused by Fusarium meridionale and F. graminearum: aggressiveness and mycotoxin production in the field
Gibberella ear (GER) and stalk rot (GSR) of maize in Brazil are caused mainly by Fusarium meridionale, while F. graminearum is the more common cause of Fusarium Head Blight (FHB) on wheat. Our previous study of two maize isolates of each species suggested that this pattern of dominance may be due to greater aggressiveness and competitiveness of F. meridionale on maize. Here we have evaluated pathogenicity and toxigenicity of 16 isolates of F. graminearum and 24 isolates of F. meridionale recovered from both wheat and maize. Strains were individually inoculated into ears of four maize hybrids in field trials. GER severity varied significantly among isolates within each species. Although ranges overlapped, average GER severity induced by F. meridionale (13.9%) was two times higher than F. graminearum (7.2%) for isolates obtained from maize, but similar for those isolated from wheat (11.8 and 10.6% respectively). In contrast, severity of GSR was slightly numerically higher for F. graminearum (18.4%) versus F. meridionale (16.1%), with no effect of host of origin. Deoxynivalenol (DON) and its acetylated form 15ADON were the main mycotoxins produced by F. graminearum (7/16 strains), while nivalenol (NIV) was the only toxin produced by F. meridionale (17/24 strains). Six isolates of F. graminearum also produced zearalenone. Results confirm that F. meridionale from maize is, on average, more aggressive on maize, but suggest greater complexity related to diversity among individual isolates within each species. Further studies involving other components of the disease cycle may help to more fully explain the observed pattern of host dominance.