Connection between primary Fusarium inoculum on gramineous weeds, crop residues and soil samples and the final population on wheat ears in Flanders, Belgium

Fusarium head blight (FHB) is a devastating wheat disease and is influenced by weather conditions and agronomic factors. Since FHB is a mostly monocyclic disease, the quantity of primary inoculum is a key factor influencing its incidence. To investigate the connection between the primary Fusarium inoculum and the final population on wheat ears, naturally occurring populations of Fusarium avenaceum, Fusarium culmorum, Fusarium graminearum, Fusarium poae and Microdochium nivale were studied at eight locations in Flanders, Belgium during the growing seasons of 2008-2009 and 2009-2010. To determine the composition of the primary inoculums in November, weeds, wheat and maize residues as well as soil samples were examined. At the end of the growing season, in July, the population on wheat ears was determined. In both growing seasons, the population was characterized by a large complexity and a differential composition at each location and for each type of sample. Nevertheless, some clear correspondences were observed: F. culmorum was a predominant species in crop residues and in soil samples in November, while the population on wheat ears in July consisted mainly of F. graminearum and F. poae, with only a lower frequency of F. culmorum, indicating that soil is not an important source of primary inoculum. The presence of M. nivale was restricted to weeds, crop residues and soil samples in November, and was nearly absent in July at the majority of locations. Finally, our results also indicate that the Fusarium population in July is more complex than the population at the beginning of the season in November. The information of the primary inoculum and the composition of the FHB population at the end of the growing season is important to predict FHB incidence and to implement control strategies for FHB.