Saprophytic survival of Fusarium graminearum in crop residues

Fusarium Head Blight (FHB) is one of the most important disease altering wheat crops. A field experiment was conducted to better understand the saprotrophic development of Fusarium graminearum and its consequences on FHB, to characterize the relative importance of the different sources of FHB inoculum and the accumulation of mycotoxins in grains and subsequently, to determine early indicators of future disease development on ears and accumulation of mycotoxins in grains. The development of F. graminearum in the soil and crop residues was monitored in controlled conditions. The inoculum hosted by seeds and/or buried with crop residues in the topsoil had only an effect on the winter development of the disease. In contrast, the main source of inoculum causing FHB disease on ears and accumulation of mycotoxins in wheat kernels came from residues left on the soil surface. Monitoring of plant development from sowing to harvest, crop management and soil and weather conditions produced a large database. Unfortunately, the role of climate was decisive in the development of the Fusarium-host plant interaction, thus prevented the use of early indicators to accurately predict the risks of yield losses and accumulation of mycotoxins involved. F. graminearum was regulated by the soil microflora. However, crop residues provide the fungus spatial and trophic niches favourable to its development. The exploitation of these niches by F. graminearum depends on the nature (previous crop and C/N) of the residues. Maize stubbles provide a greater carrying capacity than wheat straw and rapeseed residues while mustard has a suppressive effect for the fungus. The management of crop residues is a key point to control the development of FHB. A strong emphasis should be placed on the biological decomposition of crop residues at the soil surface or/and on the use of suppressive intermediate crops such as mustard to limit the soil inoculum potential of saprotrophic F. graminearum.