Abstract
Fusarium graminearum (Gibberella zeae) is a major cause of cereal scab, in particular Fusarium scab (head blight) of wheat. DNA sequence analyses have been used to define nine phylogenetic lineages that have been accorded species rank. In this study, we used DNA sequence from four nuclear genes (MAT1-1-3, beta-tubulin, Reductase, and Tri101) and amplified fragment length polymorphisms (AFLPs) to determine if hybrids between these lineages were present under field conditions. We analyzed more than 400 isolates of F. graminearum collected from wheat and sorghum at nine locations in Brazil and Uruguay. Six lineages (1, 2, 6, 7, 8, and 9) of F. graminearum were represented in these locations. Lineage 7 isolates were recovered from all the locations and represented >70% of the sample. Isolates of lineage 9 were recovered from only one location (Uruguay). We found hybrids between lineages 1 and 7, 2 and 7, and 7 and 8. Our data suggest that there are no substantial barriers to gene flow between different lineages present at the same location, and that the different phylogenetic lineages belong to a single biological species.