Survival of Fusarium graminearum, the causal agent of Fusarium head blight. A review

Wheat is one of the most cultivated crops worldwide. In 2010, 20 % of wheat and durum wheat were cultivated in Europe, 17 % in China and 9 % in Russia and in North America. Wheat yield can be highly decreased by several factors. In particular Fusarium graminearum Schwabe is a worldwide fungal pest impacting wheat production. F. graminearum is the causal agent of Fusarium head blight, root and stem-base rot of cereals. Losses caused by Fusarium head blight in Northern and Central America from 1998 to 2002 reached $2.7 billion. Moreover, F. graminearum produces mycotoxins which affect human and animal health. The threshold of these mycotoxins in foodstuffs is regulated in Europe since 2007. F. graminearum survives for several years saprotrophically in the soil, on dead organic matter, particularly on crop residues. F. graminearum adapts to a wide range of environmental variations, and produces extracellular enzymes allowing feeding on different crop residues. However, F. graminearum competes with other decomposers such as other Fusarium spp. belonging to the same complex of species. Actually, it is not known whether F. graminearum mycotoxins give F. graminearum a competitive advantage during the saprotrophic period. Anthropogenic factors including preceding crops, tillage system and weed management can alter the development of the soil biota, which in turn can change the saprotrophic development of F. graminearum and disease risk. We review the ecological requirements of F. graminearum saprotrophic persistence. The major conclusions are: (1) temperature, water, light and O-2 are key conditions for F. graminearum growth and the development of its sexual reproduction structures on crop residues, although the fungus can resist for a long time under extreme conditions. (2) F. graminearum survival is enhanced by high quantities of available crop residues and by rich residues, while sexual reproduction structures occur on poor residues. (3) F. graminearum is a poor competitor over time for residues decomposition. F. graminearum survival can be controlled by the enhancement of the decomposition processes by other organisms. In addition, the development of F. graminearum on crop residues can be limited by antagonistic fungi and soil animals growing at the expense of F. graminearum-infested residues. (4) Agricultural practices are key factors for the control of F. graminearum survival. A suitable crop rotation and an inversive tillage can limit the risk of Fusarium head blight development.